Download stability of terrestrial ecosystems as to pest organisms

G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
http://www.icfcst.kiev.ua/VASECHKO/Vasechko.html
[email protected]
12_Axiom2-1.doc
2.1.2.3. SUPERTOLERANCE to PLANT PESTS
2.1.2.3.1. Supertolerance to herbivores
2.1.2.3.1.1. Compensation of losses in seed and seedling stages
An operation of CESPPs 2.1.2.3. is based on the fact that seed production of plants is
extremely redundant. It is much greater than the possibility of their progeny to survive to the age
of maturity. In fact, P.S. Pogrebnyak (1968, pp. 310-312) has cited a number of scholars, who
show the annual values of seed yield of dominants in forest ecosystems. In coniferous tree
species, the average values equal roughly 25 million of viable seeds per hectare at the good
yield. Hence, over one forest generation (200 years in coniferous species), at beginning of
yielding in 20 years and at the good yield every fourth season, a hectare of forest can produce
above a billion of seeds.
Approximately 90% of seeds of the spruce, the fir or the larch are eaten by vertebrate
consumers on the soil surface during winter (Vladyshevsky, 1984). Because in the beginning the
period of seed producing, density of forest trees composes approximately a thousand per hectare,
it is need for regeneration of this area only 1/10.000 part of the seed yield, which has not been
consumed by herbivores in tree crowns and the soil surface.
The number of seedlings in the first season after good year usually reaches of several
hundreds of thousands per hectare. If a forest cover continues to be closed, in several years only
a few seedlings survive – 1/100.000 part of a one-year progeny. Further, the most part of them is
condemned to perish even at a lack of PPs dying due to competition with older trees. However, a
minute surviving part of the progeny is accumulated during a number of decades and ensures the
shift of an old generation of dominants with a new generation. Thus, the consuming by PPs of
most part of seeds of dominants and their juvenile regrowth does not exert any effect on
character of an ecosystem.
This picture is true on condition that the presence of limitations for activity of consumers of
seeds and juvenile plants. The limitations are posed by natural enemies of herbivores. The
importance of the enemies gets obvious if consider the situation where their activity is
suppressed by human interference.
A part of acorns yield in the English oak is destroyed commonly by the weevil Balanus
glandium Marsch. as well as the moths Carpocapsa splendana Hb. and C. amplana Hb. It was
showed that in undisturbed by humans ecosystems, losses of acorns due to these species spread
on less part of yield, whereas at disturbances connected with grazing (a lack of undergrowth and
grass cover, the trampled down soil) the losses grew to values, when it was difficult to gather
seeds for forest regeneration. Z.S. Golovyanko (1950), who discovered this fact, supposed that
the high damage due to these pests was a result of low activity of their natural enemies in
disturbed oak forests.
Now, the establishing of forest stands by sowing of acorns becomes a difficult problem,
because they are eaten by numerous rodents and wild boars. High density of these animals is
explained by providing them with additional food (in areas of intensive agriculture) and
suppression of their predators by people.
In the conditions, where predators of game animals are wiped out (hunting husbandry, and
some reserves) and multiplication of these animals is not regulated, it is common a heavy
damage of forest regeneration by them. In this respect, particular bad management and
ecological illiteracy are characteristic for the Soviet and Post-Soviet societies. Their literature
abounds in reports about such cases.
Thus, it is the grounds to state that to be effective as CESPPs, 2.1.2.3.1. "Supertolerance to
herbivores" should cooperate with 2.2.2.2. "Natural enemies of vertebrate herbivores."
78
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Here are further examples of operation of CESPPs A.2.1.2.3.1.1. "Compensation of losses in
seed and seedling stages." It is well known in the apple-trees. The losses up to 90% of the
ovaries due to consumption by the apple blossom weevil, Anthonomus pomorum L. does not
decrease yield of apples; in the conditions of the absence of this insect, the same part of the
ovaries would fall away (V.A. Grodsky, pers. comm.).
In fact, in an apple-tree, even at control of pest insects, a yearly fall of ovaries is common in
the range of 25,000 – 32,000, whereas the apple yield is 1,500 – 3,000 fruits. Hence, 93-94% of
the ovaries are redundant. A tree has no resources to provide most part of the ovaries with
nutrients. When soil fertilizers are applied and weeds are controlled, value of the fall decreases,
and fruit yield becomes greater (Anonim, 2004).
The male reproductive organs in plants, which cannot be used in further vital activity of a
tree, are rejected after pollination. Their biomass is rather significant comparing with biomass of
a tree as a whole. Nevertheless, trees do not spare these parts. In fact, every spring after
completion of blossoming, the soil surface under large trees of the poplars (Populus spp.)
becomes covered by poplar catkins. An amount of such a fall out reaches dozens of pounds per
large tree.
At advanced interrelations among host-plants and consumers of their seeds, the operation of
CESPPs 2.1.2.3.1. "Supertolerance to herbivores" has been developed into a collaboration of the
plants with seed-consuming herbivores. In so doing, the latter act as disseminators, while the
former supply them by a part of their seed yield for feeding. A great many vertebrate species
take part in this phenomenon. Consider some examples concerning coniferous tree species
according to information in the book by G.G. Doppelmeyer et al. (1966, pp. 352-354).
The main agents are the squirrels, Sciurus spp., the stripped squirrel, Eutamias sibiricus
Laxm., and the woodpeckers. The bird Nucifraga caryocatactes L., which prefers seeds (nuts) of
Pinus sibirica (Rupr.) Mayr and P. cembrae L. plays a crucial role in dissemination of these
species hiding the nuts in the soil within the range of several kilometers at the rate up to thirtyfour thousand of the nuts per hectare.
It is pertinent to paid attention on high amount of resource consumption by these herbivores.
In seasons with low yield of the nuts, this yield is consumed by vertebrate herbivores completely.
In the seasons with the abundant yield, the losses due to these herbivores, mainly the squirrels,
are evaluated as equal 75-85%. In other coniferous species, the losses also are high. Moreover,
the squirrels inflict serious damage for seed production by means of the "cutting" in winter of
spruce terminals, where they eat away "flowers" buds. It might be, the cause of high values of
the losses consists in a deficiency of consumers’ predators in present time. In fact, the active
predator of this group of herbivores - the sable, Martes zibellina L. was recently on the level of
extinction.
A lack of predators leads to heavy damage on the part of herbivores, which in undisturbed
ecosystems probably took part in dissemination of plants. This statement might be illustrated by
the rodents – serious pests of cereal crops. O.A. Grikun (pers. comm.) has observed in south of
Ukraine that rodents collect in a soil nest up to 60 kg of wheat grains of the best quality, and the
total losses of the grain are evaluated as equal 2.5 metric tons per hectare.
In above situations, CESPPs 2.1.2.3.1."Supertolerance to herbivores" is effective on
condition that a cooperation with 2.1.2.2.1. "Disappearance from herbivores" and 2.2.2.2.
"Natural enemies of vertebrate herbivores, Predators."
In deciduous plants, it is seen the trend, when plants collaborating with consumers of seeds
take some measures for limitation of seed consumption by them. The case is interrelations of the
English oak, Quercus robur L. and the European jay, Garrulus glandarius L. This bird is known
as the main agent of dissemination of acorns, and in the same time, it is a consumer of them
making no seed stores. How does this contradiction is settled?
It occurred to be, the key role is played by a form and a structure of an acorn’s surface. The
slanting form and the smooth elastic surface cause a slipping out of acorns from paws of the jay.
Usually, the birds gather several acorns in oak crowns keeping them in their mouths and gullets.
Then, they fly to shelters in a forest canopy on the distance up to several kilometers. Here, the
79
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
birds peck acorns, but a part of them slips out from their paws and falls on the soil surface, where
they get out of birds’ vision, and germinate. The protective role of the form and the structure of
an acorn surface were described by M.G. Kholodnyi (1941).
This is a case of cooperation of CESPPs 2.1.2.3.1. "Supertolerance to herbivores" with
2.1.1.2.1.1.1. "Antibiosis to herbivores, Structural, Permanent."
In the birch, Betula verrucosa Errh., catkins are damaged by the weevils of the genera Apion
and Curculio usually with the rate of several percents. A.S. Serebrovsky (1947, pp. 93-98), who
reported this fact, explain it as a result of parasite activity. However, R.I. Zemkova (1980,
pp. 14-15) showed that the low damage of catkins is peculiar only for Betula verrucosa, whereas
the exotic birch species, which grow near by this species in a botanical garden – B. lutea Michx.,
B. halii Howell, B. mandshurica Nakai, were damaged by the weevils with much greater rate –
up to 50% of catkins. This fact suggests a presence an Antibiosis (2.1.1.2.1.) in Betula verrucosa
. On the other hand, the feeding on this species by bugs, which suck a sap from the ovaries,
results in high percentage (40-96%) of hollow seeds (Zemkova, 1980, p. 15). This is
characteristic for a lack of Antibiosis. Nevertheless, due to abundant seed production, no
problems arise with regeneration of this species. Here, it takes place an operation 2.1.2.3.1.
"Supertolerance to herbivores."
The further step in development of the collaboration of plants with seed-consuming
herbivores is the producing of seed-bearing fruits. This trait has signs both 2.1.2.3.1.
"Supertolerance to herbivores" and 2.1.1.3.1.3. "Tolerance to herbivores, Indifference to losses
of host-plant tissues." Although the plants having such a trait allow to herbivores to consume a
significant part of annual increment of their biomass (in seasons with abundant seed yielding,
this is the main part of the increment), advantages of this trait are obvious. In this case, it arises a
possibility to spread seeds on the unlimited distance and secure a comfortable media for
germination of seeds. Probably, evolutionary advantage of this trait consists also in the fact that
the herbivores consume a specialized tissue (fruit parenchima), whereas the seeds bearing
hereditary information occur in safety. In fruits, CESPPs 2.1.2.3.1. "Supertolerance to
herbivores" is important as to insect herbivores, whereas vertebrate ones are actually symbionts
of these species.
At last, seed production in a plant species can be so high that an abundant consumer having
no own natural enemies is not able to stop further dissemination of this species. An example of
such a situation was provided by C.B. Haffaker (1959). The case is consumption of 98.67%
seeds of the whin, Ulex europea L. by the seed-consuming weevil, Apion ulicis Forst. in New
Zealand. This weevil was introduced in this area for control the exotic species, which had
become a weed there. In spite of high percentage of the seed consumption, complete success in
further dissemination of the whin was not achieved. This case demonstrates the great potency of
CESPPs 2.1.2.3.1. "Supertolerance to herbivores."
2.1.2.3.1. Supertolerance to herbivores
2.1.2.3.1.2. Compensation of losses at competition of plants within a stem stock
An operation of this CESPPs is demonstrated well by the phenomenon of the annual stem fall
in dominants of forest ecosystems. This is a minute part of dominants, which die annually being
as a rule colonized by stem borers – numerous species of insects of the families Scolytidae,
Cerambycidae, Buprestidae, Curculionidae, Siricidae, Cossidae, and Sesiidae. The value of the
annual stem fall depends on stocking density of dominants, and it reaches a few percents of their
stock.
If stocking density is so low that interactions among trees are absent, the annual stem fall
does not appear. Further, the annual stem fall consists moistly of the trees of lower classes of
growth. In not too old forest, the diameter of their stems is lower than annual diameter of
dominant of their ecosystem. The height of them is also lower that the average. These facts
suggest that the annual stem fall is a result of competition of dominants for vital resources. In
overmatured forest, senescent trees prevail in the annual stem fall. A demand for the resources
80
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
increases steadfastly with growth of plants that determines appearing of the annual stem fall year
after year.
So that, the losses of trees due to the competition and old age are compensated by the rest of
dominants. Stem borers take part in the process of appearing of the annual stem fall. The
participation of these herbivores does not endanger ESPPs. Therefore, these events should be
considered as an operation of CESPPs 2.1.2.3.1.2. "Compensation of losses at competition of
plants within a stem stock."
2.1.2.4. HETEROGENEITY of a STOCK of DOMINANTS
within an ECOSYSTEM
2.1.2.4.1. Hereditary heterogeneity of a stock of host-plants
The role of CESPPs 2.1.2.4.1. might be illustrated by the case of Zanduri - an ancient wheat
cultivar (such cultivars are called "land races"), which was grown over a long time in the western
Georgia (the Transcaucasus, Former Soviet Union). The resistance of it to phytopathogens was
evaluated and genetic analysis of its stock were conducted by P.M. Zhukovsky (1964, p. 107). It
has been found out that Zanduri is resistant to all the phytopathogen species, and this resistance
can be characterized by the term "field resistance." This is a situation of presence of affection
signs, particularly the leaf rust, but a negative effect of phytopathogens is absent. When growing
outside of its natural range, this cultivar was nearly immune over a number of years to all the
resident taxa of phytopathogens. There are no reports about affection of this cultivar by
arthropod herbivores that might be an indirect evidence of its resistance to these PPs.
Further, this cultivar occurred to be a mixture of three species of the wheat – Triticum
tymopheevi, var. typiana Zuk., T. zhukovskyi Men. et Eritz., and T. monoccocum L., var.
hornemani. These species are similar in their agronomic, morphological and phenological traits,
but they are far distant from each other in their heredity. They are different even as to the number
of chromosomes.
In this region, in the wild wheat taxa, it takes place the same trend – development of
heterogeneity of the stock. Here, it grows eighteen species of the genus Triticum, i.e. nearly all
the genus (Ibid., p. 90). The evolutionary process is intensive, it arises "intraspecies taxa", which
develop easily in separate species that has been shown by breeding. So, this scholar by means of
hybridization of Triticum cartlicum var. fuliginosum (Vav.) Nevski with T. tymopheevi bred the
cultivar with so peculiar traits that it was considered as a new species – T. fungicidum (Ibid.,
p. 107). The name of this species implies that the trait of Tolerance can be transformed into the
trait of Antibiosis. In the wheat taxa of this region, as to the leaf rust and the mildew, it operates
Tolerance, whereas the self-protection against the stem rust and the smut is proceeded by
Antibiosis.
The traits, particularly of T. tymopheevi, occurred to be valuable in breeding. "This species
served as a donor of resistance for a number of varieties in the USA, Australia, Canada, and
India, including the remarkable American varieties Lee and Timstein, and the Australian
Timvera. All they are high resistant to the leaf and stem rusts" (Ibid., p. 107).
This scholar explains the situation in the Transcaucasus as a common result of prolonged
coevolution of a plant species and its phytopathogens. The Transcaucasus is a part of the center
of evolving of the genus Triticum, and climatic conditions of this region are optimal for the rusts,
Puccinia spp. In such circumstances, natural selection has come on the way of heterogeneity of
plant stock. The same principle was used by people at breeding land races (Ibid., 89-91). It
should add that both natural and artificial selections have used widely the trait of Tolerance to
phytopathogens.
What is the advantage of above heterogeneity with the standpoint of resistance to PPs? This
is a situation, when PPs are forced to overcome factors of resistance of diverse nature within a
stock of their host-plants in an ecosystem. In a result of hereditary changes, it rises new
pathotypes of phytopathogens and races of herbivores, which endanger to overcome factors of
resistance of their host-plants. The resistance means Tolerance, i.e. inapparent Antibiosis, for the
81
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
leaf rust and the mildue as well as common Antibiosis as to the stem rust and the smut. When
factors of self-protection in a plant stock are divers, the probability for virulent (aggressive) PPs
to encounter susceptible host-plants becomes insignificant. 2.1.2.4.1. "Hereditary heterogeneity
of a stock of host-plants" might be the only CESPPs, which gives a chance to survive a plant
taxon at an invasion of aggressive PPs in a given area or at arising of high-virulent taxa of
indigenous species. The operation of this CESPPs in cooperation with Tolerance and Antibiosis
give the best durability of the resistance.
The complex of traits characteristic for Zanduri occurred to be very useful in the agricultural
practice. In fact, any problems with protection against phytopathogens did no arise, and the
uniformity of agronomic (morphological and phenological) traits allows minimizing other
problems of the growing.
This ancient method of protection against phytopathogens has been restored in nowadays in
the concept of intrafield diversification. According to the concept, a crop is growing as a mixture
of plants with uniform agronomic traits and diverse traits of resistance to phytopathogens. The
plants can be pure lines (Jensen, 1952) or back-crosses (Borlaug, 1959). Diverse aspects of this
concept have been discussed in N.E. Borlaug (1965), J.A. Browning and K.J. Frey (1969),
M.S. Wolfe (1985), M.R. Finckh et al.(1992).
This is the case of operation of CESPPs 2.1.2.4.1. "Hereditary heterogeneity of a stock of
host-plants." It is particularly prospective in situations, which are complicated as to high
aggressiveness of phytopathogens – the areas with hot and wet climate, at usage of developed
cultural practices with high rates of fertilization and irrigation.
In natural ecosystems, the operation of CESPPs 2.1.2.4.1. "Hereditary heterogeneity of a
stock of host-plants" might be seen in the diversity terpenoids of oleoresin within a coniferous
species. The diversity of these toxic for PPs substances in a species reaches several dozens of
entries. Actually, it is impossible to find two trees within a coniferous species with the same
composition of oleoresin. Such a diversity lays heavy obstacles for PPs to overcome Antibiosis
of their host-plants. In addition to toxic effect, oleoresin suppresses PPs as a viscid media.
Prerequisites of CESPPs 2.1.2.4.1. “Hereditary heterogeneity of a stock of host-plants” are
the following: 2.1.2.P.1. “In biocenoses, forming of dominant stock at the natural conditions”
and A.2.1.2.P.2. ” In articenoses, a resemblance of a dominant stock to that in biocenoses or
special cultural practices with the aim of effective operation of CESPPs A.2.1.2.”
2.1.2.4. HETEROGENEITY of a STOCK of DOMINANTS within an ECOSYSTEM
2.1.2.4.2. Heterogeneity of species composition within dominants
In the environmental conditions composing ecological optimum for phytopathogens, there
exists a trend of evolving ecosystems with wide diversity of species in a stock of dominants. The
greatest expression of this trend is observed in hot and wet tropical climate. Such a climate is
ideal for activity of phytopathogens. The surprising species diversity of the rain tropical forest is
a result of potent selective pressure on the part of these PPs. A stock of dominants consisting of
hundreds tree species per hectare decreases to a minimum the probability of an encountering of
pathogenic agents and susceptible hosts. In such a heterogeneity, cross-pollination of plants is
complicated. Nevertheless, the evolution overcomes this complication by means of attraction of
insects with odor simulating their pheromones. In a result, it has arisen a symbiosis between a
plant species and a definite species of insect pollinators.
Here is an example of effective operation of CESPPs 2.1.2.4.2. in protection of tree species
against phytopathogens provided by J.L. Harper (1969, p. 60): “Hevea brazilensis can be
established as a pure stand plantation crop in Malaya. In its native Brazil, pure stands cropping
proves impossible because of epidemic development of local diseases. In Brazil this species
survives effectively only where it is intersparsed in a mixed community. This finding
immidiately pinpoints the role of the pathogen in floric diversity in natural rubber communities.”
Because the phytopathogens have not penetrated into Malaya, the pure stand plantations are able
exist here without operation of CESPPs 2.1.2.4.2.
82
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The principle of an increase of heterogeneity of a stock of dominants for enhancing of
resistance of cultivated crops was used by the idea of the intrafield diversification. According to
it, a crop grows as a mixture of several cultivars distributed within a field in a mosaic pattern.
2.1.2.5. PARASITIC NONPREFERENCE and ANTIBIOSIS
2.1.2.5.1. Growth under protection of Nonpreference and
Antibiosis of other plant species
An example of CESPPs 2.1.2.5.1. might be seen in the interrelations between the common
juniper, Juniperus communis L. and the Norway spruce, Picea excelsa (abies) (L.) Link. On bare
forest edges bordering with pastures, spruce seedlings suffer heavily due to grazing. On the other
hand, on the edges with juniper bushes, spruce seedlings find protection among them. Spiny
juniper bushes with unpalatable needles limit an access of livestock, but they do not inhibit
a growth of spruce seedlings. In such a way, the juniper promotes to spread of the spruce into
open areas. When occurred under a cover of spruce trees, the juniper, being a light-requiring
species, is suppressed progressively in heavy shadow of a spruce canopy. Nevertheless, a strip of
juniper bushes moves in direction of an open area, so that weak shade of a spruce edge is
admissible for this species.
A survivorship at grazing of palatable grassy plants growing inside thickets of spiny bushes
was recorded in literature (Atstatt and O’Dowd, 1976, cited in T.A. Rabotnov, 1983, p. 57).
These cases of operation of CESPPs 2.1.2.5. "Parasitic antibiosis" will be considered later - the
Section 4 (1).
2.1.2. PLANT RESISTANCE to PLANT PESTS OPERATING on the LEVEL of a PLANT
COMMUNITY
2.1.2.1. Superevasion
2.1.2.1.2. Superevasion from phytopathogens
A.2.1.2.1.2.1. Superevasion from phytopathogens, Protection of vulnerable plant stages
by spending of them in the period of weak loading by infection
Here are the examples of operation of CESPPs A.2.1.2.1.2.1. "Superevasion from
phytopathogens, Protection of vulnerable plant stages by spending of them in the period of weak
loading by infection." As to the winter wheat, the valuable protective trait is an intensive growth
in spring. In such a case, the leaf rust and the powdery mildew do not decrease significantly
grain yield.
A.M. Schiehuber and B.T.Taker (1967) explain the resistance of early-matured wheat
varieties to the leaf rust by low amount of its agents in the period of the vulnerable stage (the
juvenile leaf tissue) of the crop. In this time, the agents are innumerous due to winter mortality.
Here, it operates A.2.1.2.1.2.1. "Superevasion from phytopathogens, Protection of vulnerable
plant stages by spending of them in the period of weak loading by infection" in cooperation with
2.4. "Periodic (bottle-neck) suppression."
On the other hand, artificial prolongation of the juvenile stage by means of mowing of wheat
stems increases of affection by the leaf rust on the regrowth. Just the mowing of wheat stems in
spring was recommended for evaluation of resistance of winter wheat entries to the leaf rust in a
breeding process (Assaul and Shelepov, 1972).
The effect of the leaf rust on grain yield depends on the stage of plant life cycle, at which
a given level of the affection is recorded (Burleigh et al., 1972). At the same percentage of the
affected area within an apical (flag) leaf, the grain yield decreases significantly if it occurs in the
stage of tillering, decreases a little at affection in the stage of early wax maturity, and increases at
affection in the stage of early grain formation. The fact of yield increase under effect of the leaf
rust might be explained by providing a host-plant by nitrogen due to fixation of it from the air.
This is the situation, when the juvenile stage of the rust coincides with the host-plant stage of
high demand to providing by nitrogen.
83
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The Evasion is supposed to be the only trait, which determines resistance of some wheat
varieties against the stem rust. Here is the report of H. Hunter and H.M. Leake (1933, pp. 14-15)
for the black stem rust, Puccinia graminis and the wheat: "Marquis is not rust-resistant in the
biological sense, but rust-escaping, since at the time of appearance of the fungus the plant is so
far advanced towards maturity that the effect of the disease is insignificant."
The principle of the escaping occurred to be very productive, and it has been used in a
number of prominent varieties. In fact, N. M. Stepanov et al. (1976, p. 19) has reported that the
stem rust resistant varieties Scout Triumph, Satanta, Parker, Warrior, Sherdy, Gage and Trapper
differ from susceptible ones only by the trait of early maturing – 10 days earlier than that in the
susceptible varieties.
Early affection of the winter wheat with the septoriosis, Septoria nodorum Berk. (in the
period from beginning of the heading to flowering stages) decreases grain yield on 17%, if an
affected area embraces more than one quarter of a flag leaf; the later it occurs, the less the
negative effect on yielding and quality of the grain (Areshnikov et al., 1990, p. 10).
As to the necrotrophic parasites, it is known that a delay with sowing date decreases affection
of the winter wheat by the root rots. In a result of the delay, the plantlets grow at temperatures,
which are admissible for vital activity of the wheat, but unfavorable for the root rots, so that the
vulnerable stage of a host-plant evades from the phytopathogens. This is a case of operation of
A.2.1.2.1.2.1."Supervasion from phytopathogens, Protection of vulnerable plant stages by
spending of them in the period of weak loading by infection" in cooperation with 2.4. "Periodic
(bottle-neck) suppression." A delay with sowing dates exerts the same suppressive effect on
affection in fall by leaf (biotrophic) parasites (Vasechko, 2001).
As to efficacy of CESPPs it is important a good state of its prerequisites. Firstly, this is
A.2.1.2.P.2. “In articenoses, a resemblance of a dominant stock to that in biocenoses or special
cultural practices with the aim of effective operation of CESPPs A.2.1.2.“ At a lack of
A.2.1.2.P.2., that takes place in particular at improper sowing dates, the vulnerable stages are
exposed to abundant agents of phytopathogens.
Further, A.2.1.2.1.2. operates on condition that a cultivar has A.2.1.1.P.1. “The hereditary
ability of a host-plant taxon (species, subspecies, phenological form, varieties, strains, hybrids,
lines) to resist against a given taxon of PPs”, and A.2.1.1.P.2. “The proper level of physiological
state of a host-plant.” A cultivar having no traits of A.2.1.2.1.2. or staying in improper
physiological state is susceptible to phytopathogens.
2.1.2.3. Supertolerance
2.1.2.3.2. Supertolerance to phytopathogens
2.1.2.3.2.1. Compensation of losses in seed and seedling stages
When lying in the soil, seeds of plants keep vitality over years or even centuries. A part of
them is consumed by herbivores and affected by phytopathogens. The survived seeds germinate,
when changes of environmental conditions allow activation of them. PPs endanger regeneration
of dominants in the seedling stage. Nevertheless, abundance of seeds and seedlings is so great
that change of generation of dominants in biocenoses proceeds successfully.
These facts give the grounds to suppose that in biocenoses, it operates CESPPs
2.1.2.3.2.1."Supertolerance to phytopathogens, Compensation of losses in seed and seedling
stages."
84
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.1.2.3. Supertolerance
2.1.2.3.2. Supertolerance to phytopathogens
2.1.2.3.2.2. and A. 2.1.2.3.2.2. Compensation of losses at competition of plants within a stem
stock
Operation of CESPPs 2.1.2.3.2.2. can be illustrated by the annual stem fall of forest
ecosystems. A characteristic of the annual stem fall from the view of ESPPs was given above at
considering of CESPPs 2.1.2.3.1.2. "Supertolerance to herbivores, Compensation of losses at
competition of plants within a stem stock." It should add to this characteristic that in producing
of the annual stem fall, it participates not only herbivores, but also phytopathogens. The latter
exert their effect on producing of the annual stem fall earlier than herbivores do it, so that in the
period of the colonization by stems borers, the most part of the trees are affected by stem and
root rots. The rots have developed in the annual stem fall over years before colonization by stem
borers.
The affection by phytopathogens does not effect negatively on vitality of the rest of
dominants. Therefore, it this case, it operates CESPPs 2.1.2.3.2. "Supertolerance to
phytopathogens."
The sowing rates of cereal crops are redundant as to the number of productive stems per unit
of area. These rates are chosen as optimal and are substantiated by usefulness of competition
among plant and stems within a plant. This competition selects most healthy stems, which give
maximal grain yield. The selection is need, because seeds are uneven in their vitality. High
percentage of seeds has inner infection. When growing, the plants produced by such seeds die off
due to diseases. Thus, mortality of part of stock of dominants due to diseases is compensated by
healthy plants. This is an operation of CESPPs A.2.1.2.3.2.2. "Supertolerance to phytopathogens,
Compensation of losses at competition of plants within a stem stock."
COMPONENTS of ECOSYSTEM STABILITY to PLANT PESTS of the CATEGORY 2.2.
NATURAL ENEMIES of PLANT PESTS
The case stories of high efficacy of natural enemies in suppression of herbivores have been
given in many publications, in particular in the reviews by H.L. Sweetman (1958), P. De Bach
(1964), C.B. Huffaker (1971), and H.C. Coppel and J. W. Mertins (1977). The data on what is
referred to in the present report as prerequisites of activity of the natural enemies are abundant,
but they need in systematization.
Consider the facts illustrating the list of the prerequisites CESPPs in diverse groups of PPs
given in the Axiom 2.
Prerequisites of CESPPs 2.2.1.Natural enemies of invertebrate herbivores
2.2.1.P.1. Adaptation of natural enemies to local climate
The role of this prerequisite becomes clear if to consider the fluctuations of activity of
parasites of the gypsy moth, Porthetria dispar in North America. In last decades of XIX century
and in the beginning of XX century, this exotic insect occurred to be a true natural hazard in
New England states of the USA. In 1905, an introduction of parasites of this species began. Its
results were excellent. Already in 1907, it took place mass mortality of the larvae, and over
following a decade and half, a general decrease of Porthetria dispar density took place on all the
infested area. However, in the middle of 1920-ies, it was observed a growth of acreage with High
density of Porthetria dispar, and a decrease of the parasitization (Burgess, 1926, p. 292).
Just in the middle of 1920-ies in the North Eastern states, there were "…several particularly
severe winters" (Burgess, 1930, p. 721). It might be, the first stressor was the severe winter of
1917-1918, when in the same States, it was observed mass mortality of the starlings, Sturnus
vulgaris introduced not long ego from Europe (Elton, 1958, Ch. 1). Severe winter of 1933-1934
in the North Eastern states led to the same consequences (Bess, 1961).
85
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The explanation of these events might be found in the fact that parasites of Porthetria dispar
were introduced into North America from southern Europe (Italy, in particular Sicily) and from
Japan. These parasites occurred to be non-adapted to hard frost in the infested area.
The problem of survivorship of Porthetria dispar parasites under an effect of winter
temperatures was considered by M.A.Hoy (1976). He observed numerous cases of "huge
overwinter mortality" (up to 95%) of Apanteles melanoscelus Ratz. – an important parasite of
Porthetria dispar. An inadequacy of climate of New England it was suggested for such
introduced parasites as Phobocampe (Hyposoter) disparis Viereck and Anastatus disparis
Ruschka.
It should agree with M.A. Hoy (1976, p. 218) in his opinion that "It seems likely that…
additional efforts is warranted… particularly using strains of races that are preadapted
climatically…"
In a number of cases, introductions of parasites occurred to be failed if the role of
climatically adapted strains or ecotypes of the same species was set aside. A review of the
literature was given by P.S. Messenger and R. van den Bosch (1969). As a limiting factor of
durable establishing in introduced parasites can be both severe winter and summer climates.
The closer climatic conditions of a native area of a natural enemy species and those in an area of
its introduction, the more probability of the success.
Little noticeable differences in climates of native and new areas of natural enemies can cause
a fail of introduction of them (Ibid., pp. 77-78). An example of such a situation is provided by
C.P. Clausen (1956). It concerns the tachinid parasite, Hyperecteina aldrichi Mesnil, which in
northern Japan holds the Japanese beetle in check. "In the United States, however, though
established, it provides only sporadic, ineffective control. This is because after hibernation
the parasite emerges earlier in the spring than the beetle do, so that most of the fly adults are
dead by the time of peak emergence…The reason for the poorer synchronization in America
seems to be related to differences in snow cover in the two environments."
The limitations related to the poor climatic adaptation might be overcome by introducing of
a number of the species with diverse demands to climate (Ibid., p. 73). The case is the
suppression of the olive scale, Parlatoria oleae Colvee in California (Huffaker et al., 1966).
"Here, a first parasite, Aphytis maculicornis (Masi) …was found to be very effective during the
winter and spring, but rather drastically inhibited by summer heat and dryness…a second
parasite, Coccophagoides utilis Doutt …thrives in the fierce summer heat and aridity of the
Central Valley of California because it develops slowly as an internal parasite and does not
emerge as an adult during the period of severity."
2.2.1.P.2. Adaptation of parasites to overcome resistance of their hosts
The cases of invasion of exotic herbivores provide us by good examples of the role of
adaptation of parasites to affect their insect hosts. Thus, during several first decades after the
invasion of Porthetria dispar in North America its larvae were sometimes "nearly covered" with
eggs of resident tachinid flies, but the flies successfully parasitize only insignificant part of the
host population (Forbush and Fernald, 1896, p. 385). In south of East Germany, in 1954 soon
after the invasion of the Colorado potato beetle, Leptinotarsa decemlineata Say in this area, up to
93% of its larvae were infested with eggs of the resident tachinid fly, Meigenia mutabilis Fll., but
larvae of the parasite cannot develop in the host (Gleiss, 1955, cited in W. Tischler, 1965).
An adaptation of a parasite to its insect host can be lost if only a single species of parasites is
used. This is a situation of selection of a host on resistance to a single parasite, which results in
appearing of unsusceptible host population after several decades of the high parasitization. The
case of such a situation concerns the larch sawfly, Pristiphora erichsonii Hartig and its parasite
Mesoleus tenthredinis Morley in central Canada (Muldrew, 1953; Turnbull and Chant, 1961).
The parasite was imported in 1910-1913 to control the exotic sawfly. The colonization was so
successful that to 1938 the parasitization reached the range 75 - 88%. After that, it began the
decrease, so that the parasitization fell to 5%. P.S.Messenger and R. van den Bosch (1969, p. 80)
who cited this case have stated: "The former host has become a non-host."
86
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
It is known the fact of opposite character – an adaptation of introduced parasites to
unforeseen hosts. In this context, it is important the report of the above-cited scholars about
Bathyplectes curculionis, a larval parasite of the alfalfa weevil, Hypera postica, which has
acquired a capacity to parasitize another exotic pest – Hypera brunneipennis (Ibid., p. 81). "…in
this case, a parasite can become adapted to an initially largely immune host within a surprisingly
short time. It is possible, of course, that this faculty exists only when the new host is closely
related to the original one."
Nevertheless, the adaptation spreads not only on closely related host species. The tachinid
fly, Compsilura concinnata Mg., introduced into USA in 1906 for control of Porthetria dispar,
twenty years after that, was able to kill more 90 resident host species (Webber, 1926), and after
a half century, the adaptation spread on 150 species butterflies and sawflies (Turnbull and Chant,
1961). The host butterflies were of the eighteen families with diverse constitutional and behavior
traits, i.e. their kinship was not close.
2.2.1.P.3. Diversity of species composition of vegetation within an ecosystem
A diversity of plant species is of crucial importance for activity of parasites and predators of
herbivores. The advantages of the prerequisite as to the parasites are the following:
1. Supplying of hymenopterous and fly parasites with food in the adult stage – nectar and
pollen. The good review of the literature was given by H.C. Coppel and J.W. Mertins
(1977).
2. The presence of flowering plants is need for fecundation of hymenopterous parasites.
This is so because males of the parasites respond to the females on condition that the
touching. It takes place when the sexes aggregate on flowers (Sweetman, 1958, Ch. 10).
3. Providing of the parasites with alternative insect hosts, which allow the parasites to
survive, when density of the main hosts stays on the Insignificant level. As an example of
such role of alternative hosts, the author is able to use own tests on exposition of eggs of
Porthetria dispar in ecosystems with diverse environmental conditions, which were
conducting over a number of years. The ecosystems were oak forests, where outbreaks of
Porthetria dispar were not recorded, oak forests in the period after decline of an outbreak
of the species, and an oak shelterbelt surrounding of an abandoned apple-tree orchard. In
all these cases, a presence of resident population of Porthetria dispar was not seen. In
particular, the egg-masses were not recorded. However, periodical observations of
released larvae showed that they occurred to be parasitized by the species characteristic
for Porthetria dispar – Apanteles spp., Hyposoter spp. Sometimes, the parasitization was
recorded in Porthetria dispar larvae, which were reared in sleeve cages on twigs of the
oak. In these cases, the parasites laid their eggs through gauze tissue of a cage. Hence, the
parasites were able to exist in the ecosystems at density of their main host – Porthetria
dispar close to Zero. An activity of other oak defoliators in these ecosystems were
obvious. Here, up to 30% of a leaf surface was usually consumed by defoliators, mainly
of the early-spring guild. Sometimes, density of these defoliators reached the High level.
Because parasites of Porthetria dispar survive at Insignificant density of their main host,
at mass immigration of larvae of this species, they are able to suppress them.
4. Alternative hosts are necessary for hibernation of some parasites of pest species. An
importance of this phenomenon was shown by K. Schedl (1936, pp. 144-152). He noted
that at lack of the alternative hosts the parasite need to hibernate in open cocoons that
causes heavy winter mortality. An availability of alternative insect hosts is considered as
important factor of efficacy of the tachinid fly, Compsilura concinnata Mg. in
suppression of Porthetria dispar (Sweetman, 1958, Ch. VII.). This parasite affects
150 lepidopterous and sawfly species of 23 families and hibernates in a half on them.
Further, Apanteles liparidis Bouche, the parasite of Porthetria dispar hibernates in
caterpillars of the European pine moth, Dendrolimus pini L. (Khanislamov et al., 1958,
p. 32). Therefore, in the mixed English oak - Scots pine stands, the parasitization of
Porthetria dispar by this species reaches a high value - 80%. The second impressive
87
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
example of the same role of an alternative host is the case reported by R.L. Doutt and R.F.
Smith (1969). The case is the circumstances, in which the grape leafhopper, Erythroneura
elegantura Osborn, the key pest of the grape in the San Joaquin Valley in California
occurred to be suppressed by its parasite Anagrus epos Girault. The suppression takes
place, when in within a two-male radius around a wine-yard, it grows wild or cultivated
species of the blackberry, Rubus spp. The blackberry is inhabited by the non-economic
leafhopper, Dikrella cruentata Gillette, which is necessary for overwintering of
Erythroneura elegantura.
5. Alternative hosts are necessary at activity of parasite species in the period, when their
main insect hosts yet stay in hibernation. It was noted that Trichogramma spp. often are
unable to establish their progeny in early spring due to lack of eggs of hosts. In sites with
abundant early spring butterflies (non-pest species), these parasites are numerous (Pavlov,
1976, p. 28).
6. Alternative hosts are necessary for parasites for fulfillment their life cycle, because some
species need in an appropriate stage of hosts. For example, Pimpla instigator L. -a pupal
parasites of the brown-tale moth, Euproctis chryzorrhoea L. becomes abundant at certain
conditions (Yemel’yanov, 1907, p. 24). In April, it needs in pupae of the blackveined
white, Aporia crategy L. In May-June, the second generation of it attacks pupae of
E. chryzorrhoea and other species. Further, the parasite establishes two-three generations.
It should find hosts in their pupal stage for development and hibernation.
7. Alternative preys inhabiting on wild plant species maintain arthropod predators of
herbivores. Here is an example (Hagen, 1976, cited in H.C. Coppel and J.W. Mertins,
1977). Wine-yards in California are endangered by the mite Eotetranychus willametii.
The damage by this species becomes insignificant if in a vicinity of wine-yards, the cane
grows. A presence of the cane promotes the predaceous mite, Metasculus occidentalis,
which feeds on non-economic mite species consuming pollen of the cane. This allows to
the predator to survive the period of Low density of Eotetranychus willametii.
There exist numerous recommendations to accompany cultivated crops by growing of plants,
which promote parasites and predators of herbivores. Such plants are used as an admixture to a
crop or by sowing on separate strips. One of early recommendation was given by
Kh.G. Kopvilem (1960). Here, it is noteworthy that relatively small areas of nectaroferous
plants, in particular the fennel and the parsnip, are able to help in protection of the cabbage from
Mamestra brassicae L. The ratio of areas planted with the cabbage to those sown by the
nectaroferous plants was recommended as 400:1. On the distance up to 400 meters affection of
the caterpillars with parasites reached 94%, 450-500 meters - 70%, 900-1000 meters –54%,
1500 meters – 33%.
An activity of avian predators of herbivores depends on diversity of plant species in an
ecosystem. A review of the literature and a list of trees and bushes, which, being present in
a forest plot, promote to an increase of species diversity and density of insectivorous birds are
given by H.L. Sweetman (1958, Ch. 12). The more plant species in an ecosystem, the much food
for the birds – insect herbivores, seeds and fruits.
As an obvious case, consider the study by G.E. MacDonald (1965) aimed to reveal the effect
of composition of vegetation in forest and its structure on indices of bird abundance. In the stand
of mixed composition (with several deciduous and coniferous species in the upper story,
abundant undergrowth and ground cover), the indices occurred to be much higher than those in
the pure red pine stands. The data are presented in the Table 21.
Table 21. Effect of forest vegetation on indices of bird abundance
Characteristics
of forest stands
Mixed
Semi-open red pine stand
Area in acres
10
12
Number
of bird species
18
6
Number
of bird pairs per ten acre
36
15
88
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Closed red pine stand
12
1
1
2.2.1.P.4. Presence of microclimate appropriate for activity of parasites and pathogens
The tiny hymenopterous parasites of insect herbivores are very sensitive to ambient air
temperatures and dryness. P. De Bach (1965) noted that in winter mortality of the parasites
always is high, and it varies within an ecosystem depending on conditions of localities. The
studies showed that the difference in average temperature of a locality, which equaled 1.6°C,
determines the difference in mortality in 19%. In more severe conditions, the difference reached
78%, and in especially severe conditions even 97%.
R. Abraham (1974) showed that in tiny (1-3 mm in length) the parasites with a subtle
sclerotized body are very sensitive to air temperatures in the flight period. Their optimum for
flight is close to 13°C. Temperatures above 20°C force them to search for shelters, because they
are endangered by mortality due to desiccation. Their susceptibility to high temperatures is
explained by high ratio of body surface to its weight. Therefore, hot and dry weather kills them if
they are unable to find shelter. The large hymenopterous species (body size 5-10 mm) have
potently sclerotized bodysurface, and therefore are able to fly in the wide range of temperatures.
The larvae of parasites are especially susceptible to desiccation before pupation and pupae.
Therefore, cocoons of tiny parasites (Apanteles spp.) have white color, which reflects sunrays.
The parasites of Porthetria dispar of the genus Apanteles, being very sensitive to heat and
dryness, often die off in small forest islands situated in the Steppe biome, and they are unable to
overcome open distance among the forest islands situated in vast grassy areas (A.G. Kotenko,
pers. comm.). The young larvae of Porthetria dispar overcome such a distance easily, so that
outbreaks of the species in the island forests are common.
M.G. Khanislamov (1958) reported that after severe winters, the parasitization of Porthetria
dispar larvae drops from 62.8% to 36.0% comparing with a previous season. The closed canopy
and multistory structure of forest mitigate winter extremes that promotes survivorship of the
parasites.
Microclimate of an ecosystem exerts potent effect of affection of defoliators with pathogens.
This is so because persistence of the infection is determined by insolation within an ecosystem.
When the canopy is open and undergrowth lacks, direct solar rays penetrate up the soil surface
producing destroying infection anywhere. Ultraviolet part of spectrum kill polyhedral infection
(for review see L.M. Tarasevich, 1975, p. 115). Survivorship of the infection depends on the
forest structure (Ibid., p. 119). The review of literature on this issue given by W.J. Mattson and
R.A. Haak (1987) shows that intensive ultraviolet radiation suppresses not only viral infection,
but also bacterial one. The more shade under a canopy, the better conditions for retention
infection of the surface of plants and the soil.
Behavior traits known in some species of defoliators should be considered as a response on
affection of pathogens, and this behavior demonstrates the suppressive effect of insolation. Thus,
diseased larvae of the nun moth, Porthetria monacha L. move to sunlit parts of trees, and stay
here. On the sunlit parts, died larvae dry out sooner than they do in the shade. Therefore, a
source of the infection disappears earlier. Because outbreaks of this species are common in highstocked forest stands, the larvae aggregate on tree tops. This trait of affected by polyhedrosis
larvae is so characteristic that in German the disease in Porthetria monacha is called
"Wipfelnkrankheit" – the tree top disease. The same trait was noted in diseased larvae of the
loblolly pine sawfly, Neodiprion taedae linearius Ross. (Young and Yearian, 1987). Outbreaks
of Porthetria dispar are common in forests with low stem density. Here, diseased larvae
aggregate on sunlit parts of stems.
Moreover, staying of the larvae on the sunlit parts gives them a chance to survive. In fact, J.
Tanaka (1976, pp. 270-271) reported that "…when virus-infected insects are reared at high
temperatures (approximately 30-37C°), they survive infection and emerge as adults…High
temperatures reduced the absorbtion and/or penetration of virus into cells, and also suppressed
the development of polyhedra." Also, H. Jnoue (1977) found out that newly molted silk worm
89
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
larvae recovered after inoculation by lethal dose of the cepticemia, Streptococcus bombycis at
keeping of them during six hours at temperature 37°C.
In forests, the favorable for parasites and pathogens microclimate exists in such patterns of
ecosystems:
i) Closed canopy.
ii) Open canopy, but with dense undergrowth.
The pattern “i” is pertinent for mesic and hydric habitats, where dominants are supplied with
the amount of moisture sufficient for developing of high stocking density, and therefore they
have a capacity to adjoin by their crowns. It is better, when in such ecosystems, there exist
developed lower story (stories) and undergrowth. Then, the microclimate is quite favorable for
survivorship of parasites at the periods of hot and dry weather (droughts) and severe winters.
Because insolation under closed canopy is minimal, agents of herbivore pathogens keep maximal
longevity their vitality. This is one of causes, why density of defoliators of the spring-summer
guild stays here on the Low level nearly always. At mass immigration of defoliators, their
densitry can be increased, but for short time.
The pattern “ii” is pertinent for xeric habitats, where due to deficiency of moistening, trees
dominating in an upper story survive up to an age of maturity on condition that they are widely
spaced. Therefore, in such conditions, closed canopy of dominants is impossible. Here, the
admissible level of development of the prerequisite 2.2.1.P.4. is provided by the pattern “ii” of
ecosystems. The presence of a dense undergrowth consisted of resistant to vertebrate herbivore
thorny and toxic brushes offers to parasites and particularly avian predators of herbivores
possibilities to keep density their hosts/preys on the Low and Intermediate levels.
Here are examples of such situations. In south France, it is common stands of the cork oak
growing at low stocking density with thick brushy undergrowth, where Porthetria dispar is not a
serious problem, but after cutting out the undergrowth (this measure is called "demaquisation"),
outbreaks of Porthetria dispar arise (Bigot et al., 1987; V.A.Kolybin, pers. comm.).
Forest stands established in the Steppe biome in Ukraine suffer usually due to outbreaks of
defoliators, in particular Porthetria dispar, and the forest decline. Nevertheless, some of the
stands are free of these problems. They are characterized by low stocking density, which allows
them to tolerate moisture deficiency in the soil, and dense brushy undergrowth. According to
reports of local foresters, outbreaks of Porthetria dispar arise here, but density of these insect
does not reach High values. Other species of defoliators are also not destructive. Thus, the proper
silvicultural practices allow maintaining microclimate admissible for natural enemies in severe
environmental conditions. Such articenoses keep ESPPs 3.2. “Lag control” to defoliators and
general stability of ecosystems up to 100 years or even more.
Microclimate of an ecosystem determines suppressive activity of parasites affecting rootfeeding herbivores. K.N. Rossikov (1910, pp. 30-31) showed how humidity of the soil effected
on a success of parasitization of the scarab beetle, Polyphylla fullo F. by the wasp, Microphtalma
disjuneta Wied. In ecosystems with a closed canopy, the soil surface is shaded, and therefore
moisture of an upper layer of the soil is sufficient for inhabiting of grubs of this species. Young
larvae of the parasite are able to penetrate on such a depth and to affect this host. On the other
hand, in the dry soil, the grubs stay in a deeper layer, where they nearly inaccessible for the
parasite. Even if the parasite larvae reach the grubs in the soil depth, the larvae are too weak to
overcome their hosts. The larvae attack the hosts trying to perch themselves on host’s body
beside its head. The weak larvae are thrown out by the grubs. An irrigation increases percentage
of the parasitization (Ibid., pp. 72-73).
In grassy ecosystems (steppes, meadows, abandoned fields), microclimate is determined by
density of grass stems. If the density is high, relative humidity of air within this stand reaches
values, which promote activity of pathogens of arthropod herbivores. There, the latter are kept on
the Low level of density. The locusts concentrate in plots with sparse vegetation. The cereal flies
prefer to oviposit on sparsely growing plants protecting their progeny against pathogens.
90
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.2.1.P.5. Abundance of ecological niches within ecosystems
2.2.1.P.5.1. Age and structural diversity of vegetation - a presence of several stories
of woody vegetation, and undergrowth (in forest ecosystems)
The presence in forest ecosystems of large (old) trees is vitally important for inhabiting, in
particular, the woodpeckers. These birds needs in old trees for nesting, especially aspen trees. In
the annual stem fall of large trees and dying brunches of living trees, they find their winter food
– large larvae of stem borers. The diversity of entire bird fauna is richest at presence of several
stories and undergrowth (MacArthur and MacArthur, 1961, cited in E.P. Odum, 1975).
The parasites and invertebrate predators, as well as the bats flourish also at presence old trees
and a multistory structure. In such conditions, there exist an abundance of shelters (tree holes
etc.), where they hibernate, hide during severe weather situation or spend in inactivity a part of
24-hour period.
It has been shown that a number of plants in forest ground cover, in particular Listera ovata
R.Br., Neottia nidus avis Rich., Calluna vulgaris Salisb., and Mentha arvensis L. are pollinated
by parasites of insect herbivores (Neistadt, 1948, pp.142, 334, 366). It is supposed that nectar
and pollen of these plants are necessary for imaginal feeding of the parasites, and the plants can
be indispensable for activity of the parasites.
The structure 2.2.1.P.5.1. of ecosystems provides the natural enemies with favorable
microclimate due to a closed canopy (2.2.1.P.4., pattern “i”) that in the cooperation with
2.2.1.P.1. results in ESPPs 3.1. "Proper control" for the spring-summer, summer-fall, and fallspring guilds of defoliators of deciduous tree species.
When in ecosystems, it takes place an open canopy, but with dense undergrowth (2.2.1.P.4.,
pattern “ii”), ESPPs for these guilds stays on the level 3.2. "Lag control."
2.2.1.P.5. Abundance of ecological niches within ecosystems
2.2.1.P.5.2. Microrelief diversity within an ecosystem and
the area - wide heterogeneity – a presence habitats necessary
for temporary migrations of natural enemies of invertebrate herbivores,
which are located within a reach by these species
Little depressions on the soil surface, where water stays over long time, are necessary for
living of frogs and other Amphibia, whose role as predators of insect herbivores is considered as
significant (Sweetman, 1958, Ch.12). Such reservoirs provide birds with water for drinking.
Ravines are useful in term of conservation of flowering plants even at drought that provides
insect parasites with imaginal feeding.
Refuges for alternative hosts outside of ecosystems might have a crucial importance for
suppression an insect pest with a parasite (Doutt and Smith, 1969).
2.2.1.P.6. Undisturbed state of the soil surface
The undisturbed state of the soil surface is a prerequisite of high activity of forest ants,
hibernation of some parasite species, and activity of predaceous rodents. As to the latter, it is
available the comparative data of efficacy of their predation depending on a state of forest litter.
This factor is especially influential on density of sawflies, whose cocoons overwinter in this
media (for review see H.C. Coppel and J.W. Mertins, 1977, Sections 3.5.4.). In habitats with
thick forest litter, density of the shrew, Sores spp. is sufficient for suppression of many species of
the sawflies. In Canada, in the plots with active Sores cinerus Kerr., it is unknown outbreaks of
the larch sawfly, Pristifora erichsonii Hart., the yellowheaded spruce sawfly, Pikonema
alaskensis Rohwer, and others. In Siberia, Sores arancus L. is an effective predator of the
European pine sawfly, Neodiprion sertifer Geoffr. (Kolomiets et al., 1972,p. 100).
The absence of flooding is necessary for activity of natural enemies, which spend a part of
their life cycle in the upper layer of the soil. In particular, in flood plains, outbreaks of
91
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Operophthera brumata are common. This fact might be explained by wiping out on these areas
of the parasite Cyzenis albicans Fall. Its pupae over 5-6 months stay in forest litter.
V.A. Lozinsky (1960) showed the dependence of density of Porthetria dispar egg-masses on
duration of flooding and height of swelling water. He observed an average density of the eggmasses equaled 0.63 pieces per tree on a terrain along a river bank that was flooded less a month
with water swell less than 1.5 feet, while the density reached 8.1 egg-masses per tree in
depressions, where flooding continued more than a month with the swell up to three feet. In the
first case, nearly three carabid beetles were recorded per one square meter of the soil surface,
whereas in the second case, the beetles were absent.
2.2.1.P.7. Size of area of an ecosystem sufficient for providing of natural enemies with vital
requirements
There exist a minimal area that able to provide a carnivorous species with vital resources.
Unfortunately, this fact becomes clear mainly, when species distinct due to a decrease of the area
below the lowest limit. This is true, for example, for the greatest woodpecker of North America,
Campephilus principalis (Ehrenfeld, 1970). This species due to its large size and high
specialization (it feeds by only dendrophilous insects) needs in spacious foraging areas –
6.5-8.0 square kilometers per pair. When large forest tracts in southeastern USA occurred to be
broken in little islands, this species disappeared.
The prerequisite 2.2.1.P.7. is important for activity of parasites of insect herbivores. This
supposition is based on observations by A.G. Kotenko (1977). He studied the situation in forest
stands in the Low- Dnieper area (Ukraine). Here, forest islands consist of from several dozens to
several hundreds of trees, mainly the English oak and the aspen. They grow in depressed terrain
scattering in a Steppe biome. The structure of such ecosystems is rather well with a closed
canopy and a developed undergrowth. Over recent decades, they have not been affected by
grazing. The climate of this territory is typical one for the Steppe biome with rare rains in
summer. Outbreaks of Porthetria dispar in such ecosystems are short, and heavy defoliation is
absent.
A.G.Kotenko (pers. comm.) has supposed that in above ecosystems at a decline of Porthetria
dispar outbreaks, its parasites die off nearly completely due to absence of alternative insect
hosts. This is an effect of a small area of a forest stand. The extinction of parasites provokes
repeated growth of Porthetria dispar density. Importantly, Porthetria dispar has a better chance
to penetrate into a forest island through an open area than its tiny hymenopterous parasites do.
Although with a lag, the parasites penetrate in the arising outbreaks. After penetration of the
parasites in a forest island, their density grows quickly, because the vital conditions for them are
favorable in these ecosystems. Soon, they suppress outbreaks of Porthetria dispar. Thus, this is a
case of ESPPs of the level 3.2. "Lag control."
A.G. Kotenko (pers. comm.) has proposed to bring into the forest islands egg-masses of
Porthetria dispar in the innocuous phase with the aim of providing of the parasites with the host.
A benefit of such a measure for maintenance Low density of Porthetria dispar has been
demonstrated by M. Maksimovich et al. (1968). A presence of the parasites lays obstacles to
growth of Porthetria dispar density.
2.2.1.P.8. Presence of annual stem fall (in woody ecosystems)
The annual stem fall is a minute percentage of the overall number of trees in a given
ecosystem, which die off in a result of competition and/or old age annually. This is ecological
niche of stem borers on the level ESPPs 3.1. "Proper control" and numerous species of satellites
of stem borers. The insects inhabiting the annual stem fall is nearly the only food of the
woodpeckers in winter. The annual stem fall maintains biodiversity of ecosystems, that brings
contribution not only in ESPPs, but also needs for the substance turnover, i.e. promotes the
general stability of ecosystems.
92
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
It should exert every effort on protection of the annual stem fall from a withdrawal.
2.2.1.P.9. Presence of effective vectors of pathogens
The essence of this prerequisite will be shown in the next section.
Complex effects of natural enemies of herbivores at proper operation of prerequisites of
CESPPs
1. The synergic effect at suppression of herbivores
A good state of all the prerequisites of CESPPs 2.2.1. "Natural enemies of invertebrate
herbivores" results in a developing within an ecosystem a special subsystem, where parasites,
predators and pathogens of herbivores operate in a cooperation. A protective potential of this
subsystem is so high that the most species of herbivores exist in the Low or Insignificant
densities at any weather situation. Only those herbivore species, which do not exert noticeable
effect on vitality of host-plants are able to reach High density (the early-spring guild of oak
defoliators). It should note that the suggestion as to the principal role of natural enemies
concerns the cases of operation of CESPPs 2.1.1.3.1. "Tolerance to herbivores" and CESPPs
2.1.1.4.1. "Evasion from herbivores", rather than CESPPs 2.1.1.2.1. "Antibiosis to herbivores."
At the complex effect of natural enemies of insect defoliators, the chain of causes and
sequences is the following. In forest ecosystems, due to natural processes, it arises environment
with optimal conditions for existence of all the natural enemies of the defoliators – microclimate,
food resources and shelters. Parasites and predators not only kill the defoliators, but also serve as
means of transmission of their pathogens.
When the stinging (hymenopterous) wasps try to lay their eggs in insect hosts, most of the
stingings occurred to be ineffective for oviposition, in particular due to protective behavior of the
preys. Healthy matured caterpillars are able to repulse parasites. But at stinging, it takes place
inoculation of the hosts with pathogens. One of early reports on this issue was done by
N.M. Payne (1933).
As to Porthetria dispar, R.W. Campbell (1963) reported the following values of the exceed
of empty stingings over successful (resulted in oviposition) ones in various species of parasites:
Itoplectis conquisitor Say – 200 times, Pimpla pedalis Cress – 20 times, Theronia atalanta Poda
– 4 times. The additional data on this issue were offered by B. Raimo et al. (1977).
The important role of parasites as vectors of infection was stressed by G.A. Viktorov (1976).
In turn, pathogens promote to their vectors retarding development of insect hosts that
favorable for vitality of the parasites. This phenomenon was shown for Porthetria dispar by
R.M. Weseloh et al. (1983).
Common gnats might be important vectors of pathogens within caterpillars, when their
parasites are in shortage. Ja. Weiser (1972, p. 259) was the first scholar, who showed that gnats
served as vectors of pathogens of insect herbivores. The role of these vectors was especially
significant in flood plains.
The role of parasites as vectors of pathogens can be demonstrated clearly by the cases with
exotic herbivore species. It takes place the explosion of their density in the conditions of inability
of resident parasites to vector of pathogens, whereas impressive affection of these herbivores by
the pathogens arises after importation of stinging parasites.
The comprehensive report about a pest status of Porthetria dispar during nearly three
decades after its invading into North America stated that "A very careful watch has been kept for
any indication of vegetable parasites, either fungi or microbes, and nothing has thus far been
discovered" (Forbush and Fernald, 1896, p. 405).
In 1905, it began the introducing of parasites of Porthetria dispar from Europe into North
America, and in 1907, "…destruction of the gypsy moth due to disease in North America was
firstly noticed"; in spring of 1908, "… myriad of caterpillars in the first stage were found wilting
in the forest Melrose, and when just a little later practically every caterpillar was destroyed in
one particular locality" (Howard and Fiske, 1911, p. 98).
93
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Parasites as vectors of infections can be a more important factor of suppression of Porthetria
dispar than those as a direct mortality factor. Here is a case, when parasites were unable to
induce infection probably due to very advanced immunity of the insect to pathogens. In such
conditions, an outbreak of Porthetria dispar continued over long time in spite of the high
percentage of parasitism. Such a case was described by W.F. Fiske (1913, cited in R.W.
Campbell et al., 1978, p. 42), namely: "Two outbreak areas in southern Italy, where there were
varied and abundant parasites but no sign of wilt disease, were observed. Parasites killed 90
percent but the invasion spread back and forth over the area, defoliating a part each year so that
trees were defoliated every 2 or 3 years for more than a decade."
The mass mortality of exotic herbivores due to pathogens after introducing of their parasites
was recorded for a number species. This is known for the sawfly, Diprion hercyniae Hartig
(Baird, 1956; Cameron, 1956, cited in H.C. Copper and J.W. Mertins, 1977); the winter moth,
Operophthera brumata L. after introducing in 1954-1958 of six species of parasites, whereas a
virus diseases was recorded in 1961(Embree, 1971, cited in H.C. Coppel and J.W. Mertins,
1977); for the Japanese beetle, Popillia japonica Newm. after introducing between 1920 and
1933 thirty-four species of parasites from Orient, and soon the milky diseases appeared (Carson,
1962, pp. 96-97).
Below, it is shown the examples of vectoring of pathogens are known in predators of insect
defoliators.
The sarcophagid flies attack large larvae of the defoliators piercing their skin and sucking
hemolymph; also, they suck the hemolymph, which exuded in a result of stinging by
ichneumonid parasites (Campbell, 1963). An inoculation of infection is probable at these attacks.
Polyhedral particles pathogenic for Porthetria dispar were found out on bodies of diverse
predators – the carabid beetle, Calosoma sycophanta L., ants and mites (Allen, 1916). Polyhedral
viruses were discovered in feces of carabid beetles (Capinera and Barbosa, 1975), and in many
vertebrate predators, namely: birds Cyanocitta cristata, Pepilo crysthrophthalmus, the whitefooted mouse, Peromyscus leucopus, the red-backed mouse, Clethrionomys gapperi, the racoon,
Procyon lotor, the stripped squirrel, Tamias striatus (Latenschlager et al., 1980).
It has been proved that virus particles, which have passed through an alimentary duct of
predators, retain their vitality. C.H. Andrewes (1976, Ch.14) reported that a viable virus of the
European pine sawfly, Neodiprion sertifer Geoff. was found out in feces of the predaceous bug,
Rhinocoris sp. and birds Erithacees. Also, polyhedral particles virulent for their insect hosts after
passing through an alimentary duct were found out in sarcophagid flies (Hostetter, 1971, cited in
L.M. Tarasevich, 1975, p. 119).
The microsporidia, Protozoa spp., which are known as pathogens in various species of
defoliators, are vectored by the wide range of entomophagous organisms. The facts concerned
this issue has been presented by I.V. Issi (1968). It is important the role of sarcophagid flies,
predacious beetles, ants and birds. Due to activity of predators, microsporidian infection is
common on foliage. As to the parasite vectors, this scholar mentioned A. Paillot (1924), who
studied an affection of the cabbage white butterfly, Pieris brassicae L. by the microsporidia
Thelohanis mesnii Paillot. The parasite wasp Apanteles glomeratus L. was the only vector of this
pathogen. That is why epidemics of microsporidian diseases in this butterfly occur, when density
of the parasite becomes High. The only vector of infection is characteristic for simple
ecosystems - articenoses of cabbage fields.
The predators disseminate agents of herbivore pathogens on any surface within an ecosystem.
For affection of defoliators is especially important a presence of infection on their food – foliage
of host-plants. Durable retention of vitality of the infection is possible on condition that
appropriate microclimate within an ecosystem – low insolation and high humidity of air. That is
why it is important to keep proper character of the vegetation, i.e. a closed canopy and a
multistory structure.
I.D. Belanovsky (1930) has put a hypothesis that stinging parasites and blood-sucking
predators, for example the bugs, when vectoring the inapparent infection over a population of
their hosts (preys), not only spread the infection, but also enhance its virulence. This is so
94
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
because a single enemy attacks numerous host individuals. In so doing, it takes place a situation
similar the passage of strains known in the laboratory practice. Due to natural selection in host
bodies at the passage, most virulent strains survive. In a result, the inapparent infection becomes
the acute one, and epidemics affect of the hosts both as a laboratory party and as a population in
nature.
Importantly, the process of enhancing of the virulence takes place within hosts of a single
species. In them, having the equal immune system, the selection goes in one direction. If the
hosts belong to diverse species, the selection is undirected, and, therefore, the virulence is not
enhanced. That is why in the ecosystems with rich fauna of defoliators, virulence of their
pathogens does not reach high level.
When the prerequisites are perfect, the parasites preclude both growth of density of
defoliators to High level and extinction of them in an ecosystem. At an opposite situation, it
takes place an outbreak of a single species or innumerous ones with a subsequent decline nearly
to extinction of these species of defoliators.
The role of insectivorous birds as predators of herbivores is well known. A pare of the
starlings is able to clean from Porthetria dispar up to seventy trees, and forty trees – from
Tortrix viridana within a vicinity of its nest (Anokhina and Golovanova, 1980). The tests on
isolation of defoliators from birds with nets showed that the role of them is no less than that of
the parasites in maintenance of high level of ESPPs. Such studies were conducted in particular
by G.E. Korol’kova ( 1957).
Wandering flocks of the birds are able to destroy all the population in small infestation spots
in forests and in fields. As to the latter, it is interesting the report by J.D. Harper (1983). In the
state Alabama, it was observed useful activity of migrating to the south flocks of the western
palm warbler, Dendroica palmarum palmarum in a soybean field with High density of the
soybean looper, Pseudoplusia includens. For three day, the birds decreased density of the pest
from 6.6. to 0.3 larvae per meter of a plant row.
The insectivorous birds are not serious competitors of parasites. In this context, it should cite
G.E. Korol’kova (1963, p. 102). "Usually birds at not too significant parasitization of larvae and
pupae chose healthy insects…This was also noted in literature. Strokov (1956) stated that on a
plot with attraction of birds in artificial nests, parasitization of gypsy moth larvae was twice as
much as outside of it. The same Shilova-Krassova (1953) reported, who studied predation of
birds on the Malacosoma nestria L., Tortrix viridana L., and Panolis flammea Schiff.,
Osmolovskaya (1958) – on Arge pullata Zadd., Kurazhskovsky (1958) and others. In the tests
conducted by these scholars, birds consumed parasitized larvae only at high percentage of them,
and in early stages of the affection, when parasitized insects differed a little from healthy ones.
Thus, in 1952, larvae of Porthetria dispar were parasitized by Apanteles porthetria Mues. on
80% in the conditions of protection against birds by a net, whereas the parasitation was 43% in
the check. At such an affection by parasites, the birds had no possibility of the choice, and were
forced to consume parasitized larvae. The birds decreased density of larvae greater than parasites
did (Table 23). Only late-instar larvae and pupae died due to parasites at higher percentage."
The selective consuming of preys is supposed for mammal predators. C.H. Buckner (1967,
p. 493) has supposed that "…a mammal may learn that a parasitized insect is less palatable than
an unparasitized insect (Buckner, 1966a; Holling, 1959)." The factual data as to this capacity
have been offered for the European pine sawfly, Neodiprion sertifer Geoffr. (Holling, 1955).
Consumption of diseased herbivores by birds and mammals promotes to dissemination of
infection within an ecosystem.
The forest ants, the family Formicidae, play the multilateral positive role in maintenance of
ESPPs. First of all, they are active predators of defoliators in the larval stage.
Omnipresence and high mobility of the ants give the grounds to suppose that they are very
common vectors of the pathogens. The red wood ant, Formica rufa L. is unable to manage
healthy middle-aged and old-aged larvae of Porthetria dispar, but it consumes the flabby
(diseased) larvae (Grimal’s’ky and Lozins’ky, 1976).
95
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The infection can be spread without consumption of diseased insects. For the inoculation, it is
sufficient a biting of larvae by ants with a subsequent refusal. This fact was reported for the
wood ant, Formica polyctena Forst., which fed by the media with Bacillus thuringiensis and had
contacts with exposed larvae of the family Chrysomelidae (Orekhov et al., 1978). In these
studies, at exposition in a forest plot Petri dishes with the media, 82% of ants from ant-hills in a
radius of several dozens meters vectored spores of the pathogen, whereas in the check plot, this
pathogen was discovered only in 9.3% of the ants. In bioassays of the scholars, if the ants bit a
larvae of Melampsora populi L. three times, this larvae died in 88-100% of cases. Among the
died larvae, 46-82% were affected with Bacillus thuringiensis.
A.A. Zakharov (1974, p. 24) paid attention on another positive effect of ants’ activity. They
protect the aphids from predators, so that density of these sap-sucking insects reaches significant
value that is safe for plants and is beneficial for parasites (hymenopterous wasps and flies) of
herbivores. The matter of fact, the aphids produce the honey-dew, which is used for imaginal
feeding by two hundred species of parasites. In a result, in forest ecosystems, where the ants are
numerous, the parasites are abundant.
Concluding, when all the prerequisites of CESPPs 2.2.1. "Natural enemies of invertebrate
herbivores" in forest ecosystems are in good state, the subcategories of this CESPPs maintain
each other. Thus, it arises the synergic suppressive effect of the great potency.
2. Dumping out the sea-saw feed-back mechanism
(i) Dumping out the unsheltering feed-back mechanism
(ii) Dumping out the genetic feed-back mechanism
A mathematical analysis of interrelations between a predator and its prey conducted by
A.I. Lotka (1925, 1934), V. Volterra (1927, 1927a, 1928, 1931,1931a), V. Volterra and
U. Dancona (1935) showed that density of these counteracting parts underwent sharp
fluctuations. Subsequent laboratory studies in the conditions of "microcosm" proved that
fluctuations of their densities indeed took place and found out the causes of the them. The causes
are of two kinds:
i) The lack of shelters for a prey that usually leads to its extinction, and then extinction of its
predator; further interrelations are possible at immigration of them.
ii) The intensive microevolutionary process, which develops protective traits in a prey that
results in an increase of its density and decrease of density of a predator; in turn, a
protected prey exerts selective pressure on a predator, so that the trend eventually
becomes inverse.
Consider the studies inspired by A.I. Lotka and V. Volterra.
As to the cause “i”, the role of shelters was proved by G.F. Gause (1933, 1934, 1935), G.F.
Gause and A.A. Witt, 1935) in particular with the infusoria – a predator, Didinium sp. and a
prey, Paramaecium sp. Thus, if in the media, inhabited by these organisms, it was added a
sediment of a barley-water, an equilibrium of densities of the predator and the prey in some test
variants was achieved. An explanation of the equilibrium consists in presence of shelters for the
preys.
The role of natural selection was demonstrated by S.P. Ivanov et al. (1938, pp. 33-34): "At
last, struggle for life can lead to selection of kinds of preys, which withstand better to attacks of a
predator (a parasite or a pathogen). The very interesting example on this regard was given by
Strelkov and Polyansky (1937). Studying the infusoria in a stomach of the goat, which might be
considered as a microcosm, they found out the wide limits of variability in the species,
Entodinium caudatum, Ophryoseolecidae… If into a stomach of a feeding by grasses goat, where
it inhabits normally the ecotype of E. caudatum "simplex" (without trichomes), to bring another
species of the infusoria - Entodinium vorax, which is a facultative predator, in a population of E.
caudatum, it grows percentage of individuals with well-developed trichomes…After a some time
in E. caudatum, the ecotype without trichomes disappears, whereas E. vorax feeds only by
96
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
alternate (vegetable) food. If E. vorax would not a facultative predator, the selection would result
in appearing of a capacity of the predator to overcome the protection of E. caudatum."
The role of shelters in population dynamics of animals has been shown in literature many
times, but this factor has no own name yet. Let it be "the unsheltering feed-back mechanism."
A necessity of shelters from natural enemies for survivorship of a prey has been noted for
very diverse animal species. The role of it might be demonstrated for such well-studied species
as Porthetria dispar.
Here is a situation, where an immigrated population of Porthetria dispar is destroyed
completely in the conditions of the absence of shelters. The case is forest plantations in the SemiDesert biome located at the distance about 80 miles of the nearest forest. Nevertheless,
Porthetria dispar penetrates into these plantations, and its eggs-masses are common at the end of
summer. However, in the same fall, they are destroyed by migrating birds, which use the
plantations in the treeless area for resting on the way to south. This case was reported by G.V.
Lindeman (pers. comm.). Why does the destroying take place? This is so because the plantations
consist of young trees, i.e. the trees with smooth bark, where the eggs-masses cannot be in
shelters. Also, the plain soil surface does not allow to the females finding a shelter for their eggs.
The second case is illustrated by the situation, where shelters are abundant, and, therefore,
Porthetria dispar exists at Intermediate density year after year consuming 40-60% of foliage of
host-trees.
Such a phenomenon was observed in Moldova, Former Soviet Union by A.G. Naumenko
(1973). This is an oak forest in the conditions of hot and dry climate hostile for activity of
parasites and pathogens, but rather favorable for avian predators of Porthetria dispar. However,
the insect has a good chance to find protection against the birds, because stems of the oaks and
rest of stumps are abounding in hollows. These trees are suppressed ones and of sprout origin.
Their stems and stumps are affected by rots resulting in appearing of hollows, where a part of the
population finds shelter against the predators.
Thus, presence of shelters stabilizes density of a prey. In such a situation, the unsheltering
feed-back mechanism does not operate.
It should note that Porthetria dispar has limited possibility to find shelters from parasites and
pathogens. Therefore, in the conditions, where they thrive, a population of Porthetria dispar
exists on the level of Insignificant density.
As to the cause “ii”, this is well-known for ecologists the genetic feed-back mechanism - the
concept developed by D. Pimentel and associates, in a number of publications, as follows:
D. Pimentel (1961, 1961a, 1963, 1963a, 1964,1968), D. Pimentel et al., 1963, 1965), D. Pimentel
and F.A. Stone, 1968, D. Pimentel and A.B. Soans, 1971).
The concept of genetic feed-back mechanism is proved by numerous facts in the fields of
ecology, plant protection against PPs, toxicology, and medicine. This is a visual demonstration
of operation of Darwinian natural selection. Indeed, if a population of any organisms undergoes
continues affection by a mortality factor, it arises within the population a resistance to this factor.
The prerequisites of the change are the following:
i) A mortality factor should be not so potent to kill all the organisms within an affected
population, and not so weak to exert a mortality of a less part of the population.
ii) The less other mortality factors interrupt the affection on a population, the sooner the
resistance appears.
The practice of medicine has shown that efficacy of any remedy is not unlimited, the time
comes, when it becomes less effective. Similarly, toxicology and plant protection learn us that a
pesticide, being used a single, losses eventually its toxicity for PPs both in the laboratory and
field conditions. The facts of a dramatic growth of resistance of a population of vertebrate and
invertebrate animals to a pathogen or a parasite are well known, and have been reported in
particular by D. Pimentel and the associates.
The genetic feed-back mechanism is characteristic for the counteractiong organisms of the
same level of organization, i.e. within insect herbivores and their parasites, pathogens, and some
invertebrate predators. Vertebrate predators of insect herbivores and some invertebrate predators,
97
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
for example the carabid beetles (the family Calasomidae), are factors of an overwhelming force.
Protection against mortality factors of such a category develops on the ways of sheltering and
mimicry.
The genetic feed-back mechanism operates widely in simple biocenoses independently to
human interference, in biocenoses with ESPPs disturbed by people, and in articenoses.
On the other hand, in rich ecosystems, it operates a potent factor dumping out fluctuations of
density in counteracting organisms in a pair "a predator – a prey." In rich ecosystems having the
excellent biodiversity, every species of invertebrate herbivores is exposed to numerous species of
predators, parasites and pathogens. Here, natural selection proceeds in numberless directions as
to all the counteracting organisms. Therefore, “a prey" keeps a moderate level of susceptibility to
“a predator", whereas the latter keeps a moderate capacity to affect its "prey." This phenomenon
was stated by D. Pimentel (1961a).
Insect hosts and their parasites exist in continual counteractions. The hosts protect themselves
by means encapsulation of eggs of parasites laid in host’s bodies. The parasites protect their eggs
from this response by masking of them with special substances. The biochemical events in this
process were studied by S. Osman (1974) on the example of hymenopterous parasite Pimpla
turionella and its several host species. The parasite’s eggs laid on larva’s skin are often casted at
molting.
Obviously that in such a counteraction, it takes place a fluctuation of the success of a parasite
or a host on a population level. That is why, values of a parasitism in insect herbivores undergo
changes year after year. The practice of introduction of parasites for suppressing exotic pest
insects has shown that a single parasite species suppresses its host during the limited period.
Contrary, introducing of numerous parasite species provides a continual suppression. This is a
simulation of a situation in rich ecosystems.
To unite above "mechanisms" under a single name, let’s use the term "the sea-saw feed-back
mechanism." It seems, an image of the children’s play "sea-saw" reflects adequately this the
simplest pattern of population dynamics of counteracting species.
Thus, the level ESPPs 3.1. “Proper control” for invertebrate herbivores is characterised by
dumping out the sea-saw feed-back mechanism.
Prerequisites of CESPPs 2.2.2. Natural enemies of vertebrate herbivores
2.2.2.P.1. Unlimited activity of predators in coopertion with CESPPs 2.4. “Periodic
(bottle-neck) suppression”
In ecosystems of diverse types (forest of grassy), where predators of vertebrate herbivores are
wiped out by people, density of the herbivores reaches High values, and they exert heavy
damage to dominants. This is a live issue, in particular, for forests of the Crimea Peninsula,
Ukraine (Mishnyov, 1970). Here, predators of hoofed animals are absent, and it is practiced a
winter additional forage of these animals, whereas hunting is insufficient. In a result, density of
the deers reaches 50 individuals per thousand of hectares, and density of all the hoofed animals
per this area – 79 individuals, although a tolerable density on the area is up to 20 deers. In a
result, a regrowth of dominants in the forests is heavy damaged by the animals.
Thus, ESPPs of the level 3.1. "Proper control" to these animals is maintained by CESPPs
2.2.2. "Natural enemies of vertebrate herbivores", 2.2.2.2. "Predators." The role of CESPPs 2.4.
"Periodic (bottle-neck) suppression" as a cooperator of CESPPs 2.2.2.2. is important. It causes
weakening of vertebrate herbivores that promotes consumption of them by predators.
2.2.2.P.2. A size of an area of an ecosystem sufficient for providing of predators with
vital requirements
98
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
For survivorship of carnivorous vertebrates, it is need certain area. Using as a food only by
natural fall of herbivorous preys (senescent individuals, weak youngsters, individuals wounded
in male tourneys), a single such a predator needs in an area that is evaluated by a number of
square kilometers. Human activity, which leads to shortage of areas inhabiting by hoofed
herbivores, endangers an extinction of carnivorous vertebrates.
In the context with the urgent problem of nature conservation, it should cite C. Spencer
(1989, pp. 48-49): "A decade ago" says Thomas Lovejoy, assistant secretary for external affairs
of Smithsonian Institution, "no scientific data existed to determine how big a rain forest should
be to preserve its health and natural balance.” In 1979 Lovejoy decided to find out the minimal
size of a rain forest needed to sustain its trees, insects, birds, mammals, and plants. It has now
been calculated that as much as 300.000 hectares, or almost three-quarters of a million acres,
must be preserved to protect the entire ecosystem of a forest. In any section smaller than this,
species begin to disappear."
Prerequisites of CESPPs 2.2.3. Natural enemies of phytopathogens
2.2.3.P.1. Growing of plants in the environmental conditions, which are favorable far
maintenance of proper physiological state of them, provide thriving of epiphytic microflora
on a surface of above-ground parts of the plants and community of saprophagous
organisms inhabiting rhizosphere. Growing of cultivars, which are able to keep proper
physiological state in severe environmental conditions
CESPPs 2.2.3.1. embraces epiphytic microflora on a surface of above-ground parts of plants
and community of soil antagonistic organisms inhabiting rhizosphere; both of these groups
produce substances (antibiotics) toxic for phytopathogens.
"Most plants support a characteristic leaf surface microflora or saprophytes and weak
parasites which grow on the small amounts of nutrients that leak out of the leaves or are present
in aphid honey dew or even in material like pollen grains deposited on the plant surface. In
temperate climates this microflora includes Cladosporium spp., Alternaria spp., "pink yeast"
(e.g. Sporololomyces) "white yeast" (e.g. Cryptococcus) and chromogenic bacteria. The activity
of all these organisms increases as the leaf senesces, but they are replaced by other species
(Helminthosporium spp.) as the leaf dies and becomes part of the plant litter. Now, it is
reasonable to assume, that each species has particular attributes that enable it to live as part of
this microbial community..." (Deacon, 1983, p. 62).
The spores of most fungi – whether saprophytes or parasites – do not germinate in soil even
though in many cases they would germinate in distilled water. They are said to be subject to
fungistasis (or bacteriostasis in the case of bacterial cells) (Ibid., p. 63).
The fungi Trichoderma spp. are known as antagonists of the honey fungus, Armillariella
mellea. Importantly to pay attention on the prerequisites, at which these antagonists are effective.
They are shown clearly by J.W. Deacon (1983 p. 60) considering the effect of fumigation of the
soil with CS2 in a forest plot affected by the honey fungus. Here is the passage: "Some of
Armillariella is killed outright by CS2 but some, because it is protected by being inside the root
tissues, is exposed to sub-lethal doses and is "weakened." Trichoderma spp. rapidly recolonize
the fumigated soil, invade the roots because Armillariella is weakened, and kill the pathogen.
The mechanism of weakening was subsequently explained by Ohr and Munnecke (1974) who
showed that Armillariella normally produces antibiotics which prevent other fungi from invading
the roots, but after exposure to sub-lethal doses of fumigant the production of antibiotics is
reduced or stopped for several days."
This report explains why in a forest stand with healthy the main stock of dominants, the
honey fungus is limited by the annual stem fall, i.e. weakened trees. On them, the fungus is
healthy and, therefore, resistant to the antagonists. Contrary, in a forest stand with a weakened
main stock of dominants, the fungus becomes to be resistant on all of this stock. Therefore, in
such a situation it needs before inoculation by the antagonists, an application of the soil with
fungicide to suppress the honey fungus.
99
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.2.3.P.2. Adaptation of hyperparasites to suppress their phytopathogen hosts
CESPPs 2.2.3.2. embraces hyperparasites (fungi, viruses and virus-like particles), which
infest phytopathogens (fungi and bacteria) that reduces virulence of the latter.
Phytopathogens suffer due to hyperparasites likely herbivores do due to parasites. Sometimes
an enemy species affects both these groups PPs. This is true for the fungus Verticilium lecanii.
J.W. Deacon (1983, p. 37) characterizes this fungus as follows: "Specifically it grows on the
pustules formed by some plant parasites as they break through the plant epidermis to sporulate –
for example the dwarf bean rust fungus Uromyces appendiculatus, the carnation rust fungus
Uromyces dianthiana, the wheat stem rust fungus Puccinia graminis… Actually it is unusual for
a fungus to parasitize both insects and other fungi, but it is not entirely unexpected. Fungal walls
and insect cuticle both contain chitin (though not necessarily as the same store component) and
fungi and insects have the same storage components (glycogen, lipids) and soluble carbohydrates
(manitol and trehalose)."
"Viruses occur in the number of fungi and cause serious commercial loss in cultivated
mushroom crops. Virus infection of fungi…decreases growth rate and sometimes the host
virulence of the fungus’’ (Baker and Cook, 1974, pp. 182-183).
"In addition, some Trichoderma spp. are mycoparasites – they parasitize other fungi as
evidenced by the fact that they are coil around and penetrate the hyphae. On this basis it is
reasonable to assume that control of other fungi is brought about at least in part by parasitism"
(Deacon, 1983, p. 73).
CESPPs 2.2.3.3. embraces predaceous fungi, which attack phytonematodes and, probably,
other groups of phytopathogens.
It was recorded a decline of the cereal cyst phytonematode, Heterodera avenae under effect
of the predacious fungi (for review see J.W. Deacon, 1983, p. 74).
It has been known the cases of decline of epiphytoties of tiresome phytopathogens. The
causes of the decline stay to be unexplained. For example, in Ukraine, in the second part of
1980-ies and in beginning of 1990-ies, it took place the epiphytoty of the false mildew of the
cucumber, Pseudoperonospora cubensis (B. et Curt) Rostow. From 1985 to 1988, the overall
yield of cucumbers decreased on 67.7% (Nedobitkin, 1992, p. 1). This was certainly an exotic
species, because all the resident varieties of the cucumber were susceptible, whereas the varieties
bred in Japan or in the Russian Far East were resistant (Ibid., p. 13). In 1990-ies, this epiphytoty
damped, although the resistant varieties did not obtain wide spread in practice. The disease was
controlled mainly by fungicides. As a cause of the decline, it might be proposed affection of the
population by viruses or virus-like secondary parasites, which adapted to this host.
Another case, supposedly concerning an adaptation of resident hyperparasites to an invaded
phytopathogen has been described by Ch. Elton (1958, Ch. VII). The mycosis of the asparagus
having no epiphytotic character in Europe penetrated to the United States, spread over the
country and actually wiped out growing of this crop. In due course, this disease became less and
less destructive, so that growing of the asparagus in the USA restored.
It should cite the report by Z. Klement and Z. Kiraly (1957) about the hyperparasitic chain on
the wheat: a rust fungus, its parasite a bacterium, and a phage parasitizing on the latter.
Thus, phytopathogens have enemies, which in turn have own enemies. In plant parasites,
there exists a chain of consumers analogous to the food chain based on animal consumers.
Microevolutionary processes in these chains are supposed to provoke similar fluctuations in
aggressiveness that results in epiphytoties rotating with many years of depressions.
These reports suggest of operation of the sea-saw mechanism in interactions of host-plants
and phytopathogens in articenoses. Contrary, in biocenoses, this mechanism is damped.
100
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
COMPONENTS of ECOSYSTEM STABILITY to PLANT PESTS of the CATEGORY
2.3. ROUTINE WEATHER SUPPRESSION
There exist the numerous reports as to diverse and potent impacts of weather situations on
PPs. As reviews, it might be recommended the publications by R.W. Henson (1968) for insect
pests, and W.H. Hogg (1970) for phytopathogens.
Now, the aim consists in illustration of CESPPs in the Table 2 by the cases of weather
situations, which exert the effects on density of PPs in space and time that can be used for
understanding of ESPPs.
It should remind some facts in this province. Every species of PPs has a complex
requirements to weather conditions (optimal, admissible, maximal and minimal ambient
temperatures, sum of effective temperatures, which need for fulfillment of a given stage of a life
cycle, humidity of media depending on amount of precipitation, etc.). Probability of situations
with definite values of the conditions is a climate of an area. The dependence of
abundance/occurrence of pest insects on climate has been shown by W.C. Cook (1929) in the
concept of bioclimatic zonation of the range of a pest insect species. Therefore, it is relevant to
consider the role of CESPPs 2.3. "Routine weather suppression" on the base of this concept.
The zonation of W.C. Cook teaches us that climate determines abundance of a species of PPs
in time and space as a whole, although diversity of the abundance within a single zone implies
that other CESPPs have important significance. The role of CESPPs 2.3. in the entire complex of
CESPPs for certain taxa or groups of insect herbivores will be shown in the Section 5(1). In the
present section, it will be considered the suppressive role of separate subcategories of CESPPs
2.3. "Routine weather suppression" per se or in a cooperation with other CESPPs.
The effect of climate is subdivided on four categories – from very favorable for a PP species
climate, which allows it to exist at High density most part of years, to very suppresive one. The
latter determines impossibility of continual presence of this species in a given area. Because
localization of the W.C. Cook’s zones is unequal for different PPs species, it is obvious that
abundance of them is determined by diverse elements of climate. In the context with ESPPs, it is
important to comprehend those of them (weather situations), which exert a suppressive effect on
PPs operating as a single CESPPs or in cooperation with other CESPPs.
There exists a species of PPs, for which the available data are so numerous that they allow
describing the role of subcategories of CESPPs 2.3. "Routine weather suppression" for all the
range of W.C. Cook’s zones. This is achieved if to compare its abundance and occurrence in a
given area, climate (the probability of weather situations) of this area, and effect of diverse
weather situations on vitality of this species. This is the gypsy moth, Porthetria dispar. The
patterns of abundance/occurrence of Porthetria dispar in the European part of Russia and the
southwest part of West Siberia correspondes well the zonation according to W.C. Cook. These
zones as though are strung on an imaged line connecting the cities Chelyabinsk and St.Petersburg (Russia).
The Chelyabinsk Region (the West Siberia) is considered as the W.C. Cook’s zone of normal
abundance (a). This is area of distinctly continental climate, where outbreaks of Porthetria
dispar are prolonged and arise with intervals close to ten years. According to the definition, the
role of CESPPs 2.3. "Routine weather suppression" is insignificant here. Indeed, this is true
concerning an arising of Porthetria dispar outbreaks, but as to a decline of the outbreaks, some
specific effects of this kind are traced.
In fact, P.M. Raspopov and P.M. Rafes (1978) observed an ever-increasing affection of the
population by pathogens. In fall of 1967, 57% of the embryos occurred to be died, in fall of
1968, the value mortality was 96%. At last, in spring of 1969, 99.76% the embryos were died.
The increase of mortality in winter allows suppose an operation of CESPPs 2.3.1. "Low ambient
temperatures at hibernation even if they are not extraordinary ones" with the effect 2.3.1.1.
"Unhatching after hibernation" at a cooperation with the effect 2.5.3.1.5. "Spontaneous or winter
mortality of embryos." The latter effect obviously prevails.
101
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
In addition, the above cited scholars recorded in 1969 at a decline of a Porthetria dispar
outbreak mortality of 92% of the older larvae under effect of parasites and polyhedrosis in spite
of density of the larvae was Low. Obviously, this population of Porthetria dispar was very
affected by the slow form of infection of this pathogen, which transformed in the acute form of
infection.
In the conditions, where the study was conducted, it is possible in summer only weak
precipitation. Therefore, this case should be considered as an operation of CESPPs 2.3.2.
"Weather stresses close to common (rains, droughts, frost) in the period of development of postembryo stages" with an effect 2.3.3.1. "Mortality under effect of the acute form of infection in
the stages of larvae, pupae, and adults" at cooperation with 2.5.3.1.4. "Mass mortality due to
affection by the acute form of infection and parasitization."
H.A. Bess (1961) observed mortality of one-third of embryos of Porthetria dispar
("unhatching of larvae") in spite of winter temperatures were close to yearly average. This
problem becomes clear if to assume that weather stresses, in particular at hibernation, eliminate
the part of the population weakened by the slow form of infection. Again, one can suggest the
cooperation of CESPPs 2.3.1.1. with effect 2.5.3.1.5. "Spontaneous or winter mortality of
embryos."
The area situated from the South Urals (Bashkiria) northwest to the Tula Region concerns the
W.C. Cook’s zone of occasional abundance (b). The interval between the outbreaks changes
from 8 to 14 years in Bashkiria to 18 years in the Tula Region. Duration of the outbreaks
decreases in the same direction. In Bashkiria, duration of them sometimes reaches ten years,
whereas on the northwest border of the zone, the outbreaks have shorter duration – less than six
years.
What kinds of CESPPs determine the difference in population dynamics of Portheria dispar
between the W.C. Cook’s zones (a) and (b), as well as the difference within the zone (b)?
Unlike to the zone (a), in the zone (b), it is possible the weather situation, which is considered
as CESPPs 2.3.3. "Cool and prolonged rains in the larval stage of defoliators" at the effect
2.3.3.1. "Mortality of larvae at inducing of the acute form of infection" in a cooperation with the
effect 2.5.3.1.4. "Mass mortality due to affection by the acute form of infection and
parasitization." Probability of the weather situation, i.e. CESPPs 2.3.3., increases from south-east
to north-west.
Areas situated close to the northwest border the zone, an onset of cool and prolonged rains is
probable at Low or Intermediate densities of Porthetria dispar. In these areas, CESPPs 2.3.3.
cooperates with CESPPs 2.2.1. "Natural enemies of invertebrate herbivores", 2.2.1.3.
"Pathogens", rather than 2.5.3.1.4. This is so because CESPPs 2.5. “Effects of crowding” do not
operate at Low and Intermediate densities.
What kind of effect exert cool and prolonged rains? I.D. Belanovsky (1936) reported that at
heavy rains, a population of Porthetria dispar perished nearly completely due to diseases no
more than over three days. The same was noted by R.W. Campbell (1973) in following words:
"…heavy precipitation in June…, if sufficiently wide spread, may indicate the abrupt collapse of
the outbreak phase…"
The decline of a Porthetria dispar population is caused by activation of the slow form of
infection. The activation is based on presence of the polyhedrosis in some insect’s tissues, which,
however, does not induce mortality of the caterpillars until they undergo stress. At the slow form
of infection, polyhedres present in epidermis, lately – muscles and nervous system, but in gut
epithelium, they do not penetrate (Tarasevich, 1975, p. 28).
Since the infectious agents are absent in feces of Porthetria dispar larvae, the feces cannot
serve as source of the infection. Therefore, transferring the infection among Porthetria dispar
larvae is possible on condition that a body cover of diseased insects becomes broken. Then, the
infection comes out. J. Komárek (1931, p. 84) reported about this phenomenon for Porthetria
monacha L. A quick breakage of integrity of an insect’s body occurs, when it is affected with a
fungal disease. The polyhedrosis spreads intensively within an insect population, when it is
combined with affection of the insects with a fungal infection.
102
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The prerequisite of activity of the fungal pathogens consists in high humidity of air. In fact,
J.W. Deacon (1983, p. 31) has reported about the fungal diseases of insects the following: "…a
high relative humidity (at near 100%) is always needed in the initial stages of infection…"
The most favorable conditions for affection by the fungal diseases arise if high humidity is
combined with the stress for host organisms. The stress is exerted by low air temperature - below
10°C. According to S. Metalnikov (1927), below this temperature, activity of phagocytes stops
completely, so that the immune system of insects fails. The probability of combination of heavy
rains with lowering of air temperatures is ever-increasing in the direction to north-west of the
range of Porthetria dispar.
Thus, mortality of Porthetria dispar larvae in the area under question is exerted by CESPPs
of the subcategory 2.3.3. "Cool and prolonged rains in the larval stage of defoliators" with the
effcct 2.3.3.1."Mortality of larvae at inducing of the acute form of infection." This effect is
possible at High density of the insect, i.e. in the outbreak phase, and at Intermediate density of
the insect, i.e. at an entering of a population in the outbreak phase. In the former situation, it
takes place the cooperation with CESPPs of the category 2.5.3.1.4. "Mass mortality due to
affection by the acute form of infection and parasitization." In the latter situation, CESPPs
2.3.3.1. cooperates with CESPPs 2.2.1. "Natural enemies of invertebrate herbivores",
2.2.1.3."Pathogens."
In the area situated to northwest from the Tula Region – the Moscow Region, the resident
population of Porthetria dispar stays nearly continually on the level of Insignificant density
(Semevsky, 1973). Here, over all the period of observations (from XIX century), it has been
recorded only three outbreaks of Porthetria dispar obviously of a migration origin and two
increases of density in resident population of the species. Therefore, this area should be
concerned as the W.C. Cook’s zone of possible abundance (c).
In this zone, cool and prolonged rains are common over all the season. This fact allows
supposing an active operation of CESPPs 2.3.3. "Cool and prolonged rains in the larval stage of
defoliators" with the effect 2.3.3.1."Mortality of larvae at inducing of the acute form of
infection."
Notably, the resident Porthetria dispar population exists in this area continually. Therefore,
activity of CESPPs 2.3.3. is insignificant to complete suppression of the population. This fact
can be explained by emancipation of the population from all the kind infection in the conditions
of Insignificant density. In result of the healthy state, the population is resistant to the effect of
CESPPs 2.3.3. "Cool and prolonged rains in the larval stage of defoliators."
At immigration of the populations from the zones (a) and (b), it takes place cooperation
CESPPs 2.2.1. "Natural enemies of invertebrate herbivores", 2.2.1.3. "Pathogens" and the effect
2.5.3.1.4. "Mass mortality due to affection by the acute form of infection and parasitization."
In the area situated northwest to the Moscow Region, outbreaks neither an immigrated
population of Porthetria dispar, nor resident one are known. A continual presence of the resident
population is dubious. The northwest border of the species is supposed to be in south of the St.Petersburg (Leningrad) Region. Butterflies of this species were recorded up to this border, but
they were probably the migrants from the south. The view as to the migration was supported by
the report of A.I. Vorontsov (1977) that in 1959, nine females of Porthetria dispar appeared in
Finland, where the resident population of the insect was unknown.
Thus, the above-mentioned area might be attributed as the W.C. Cook’s zone of possible
occurrence (d).
The destiny of these immigrated insects might be traced on the base of a study conducted by
the author. This study was conducted in the Carpathians Mountains (the Ivano-Frankivs’k
Region, Ukraine) in a locality situated approximately 800 meters above sea level. Climatic
conditions in this area are close to those on the Russian Plane situated northwest Moscow. In the
study, it was used egg-masses of Porthetria dispar collected in the Dnieper Valley in a locality
situated no more 200 meters above sea level (the Kyiv Region, Ukraine).
In so doing, the egg-masses collected on stems of the not too high birch and the aspen were
exposed at a base of birch trees, and the larvae of the first instar were used for rearing in sleeve
103
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
cages on branches of the same trees. Counting and registration of state of the exposed and caged
insects were done approximately every weak. The number of them decreases greatly with every
counting. The last larvae were found out on the trees in the fourth instar.
As to the caged insects, a minor part of them survived to the adult stage. The moths hatched
only in late September, i.e. two months later than that in the locality, where the egg-masses were
collected. The vitality of these moths was too low, so that they were unable to lay eggs. The
usage of traps with the pheromone disparlure showed the absence of attraction of Porthetria
dispar males in a season on the study, as well as in a number of other seasons.
The same effect of climate was recorded in the Alps Mountains, the Wallis District in a
locality on the elevation 1200 meters above see level (Pictet, 1919). Here, in 1907, an outbreak
of Porthetria dispar appeared. It was supposed to be the larvae were transferred by the wind
from low situated areas. This outbreak declined shortly, because low temperatures impeded
development of Porthetria dispar to such extend that the moths had no time to lay their eggs
before onset of frost.
Taking into account climate of the study area, the results of this experiment might be
explained convincingly by literature data on demands of Porthetria dispar to ambient
temperatures and humidity. The conclusions might be spread on the zone (d) in the Russian
Plane. Climate of these areas is similar being fresh and wet. Here, over all the season, it is
common cool and prolonged rains, air temperatures in nights often drop to low values; when
rains absent, it appears dew.
Consider the effects of weather situations in the W.C. Cook’s zone (d) on vital activity of
Porthetria dispar.
Although some of the reared insects survived to the adult stage, they did not lay eggs.
Therefore, in so doing, it operated CESPPs, which induced a complete suppression of the
population. In this context, it should pay attention on the fact that the moths hatched two months
lately comparing to those in the area, where the egg-masses had been collected. Probably, this is
a result of low air temperatures at nights and often appearance of dew. Taking into account that
larvae of Porthetria dispar feed mainly at nights, such a weather situation is a probable cause of
the big delay in the development. The literature data maintain such a suggestion.
I.V. Kozhanchikov (1950, p. 89) reported that for completion of the larval stage, Porthetria
dispar needed to get the sum of temperatures equaled 615.4°C (males) and 781.7°C (females)
while the pupae needed in 159°C (males) and 148°C (females). These values are high comparing
with two other species of the Orgyidae family considered in the cited book. For the completion
of the larval stage, Porthetria dispar needed in 38 days with maximal air temperature 30°C, and
121 days with maximal air temperature 18°C (Schedl, 1936, p. 59). Further, at staying
Porthetria dispar pupae of temperatures 6°C - 8°C during 24 hours, the sterility of both sexes
was observed (Emeljanov, 1924, cited in I.V. Kozhanchikov, 1950, p. 92). Such air temperatures
are usual in September in the locality of the above experiment.
As to the completion of development of embryos in the egg stage, it needs 20-25 days with
air temperatures above 0°C (Kozhanchikov, 1950, p. 372). If the adults emerged in the test in
Carpathians Mountains would lay their eggs, ripening of the embryos proceeded in the first part
of October, when in the locality it is common night frost. Such a frost would prevent the
maturation of the embryos, they would not enter into diapause and die. This is another
insurmountable obstacle for continual existence of a Porthetria dispar population in the W.C.
Cook’s zone (d).
The destructive effect of deficiency of warm at a season on Porthetria dispar was recorded
many times. P.M. Raspopov (1974, p. 237) has described these observations as follows: "In
forests of the Chelyabinsk, Sverdlovsk, and Kurgan Regions, it has been noted mass mortality of
overwintering eggs of the gypsy moth (Ocneria dispar L.), which is caused by deficiency of
warm in the summer and fall periods (1947, 1950, 1956, 1960, 1968 and 1969)… At the
deficiency of warm, the embryos inside an egg cover are not successful in development up to the
stage necessary for entering into a diapause. They die independently on severity of winter. The
highest mortality caused by the warm deficiency has been observed in the Forest biome and in
104
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
northwest part of Forest-Steppe biome, on slopes of the north exposition, on the north side of
tree stems, as well as in stands with closed canopy. In the same years, egg mortality due to the
deficiency of warm has took place in the nun moth (Ocneria monacha L.), although at less
extent."
Thus, here, it operates the potent CESPPs 2.3.4. "The sum of effective temperatures
insufficient for completion of a life cycle of a species." Its effects are CESPPs 2.3.4.1. "Mortality
in the pupal stage due to too low ambient temperature." and 2.3.4.2. "Mortality in the egg stage
due to impossibility of diapausation."
There exists one more weather situation, which creates the W.C. Cook’s zone (d). This is a
sharp fluctuation of air temperatures over all the season, which lays obstacles for continual
presence of Porthetria dispar. It is characteristic to the areas of the continental climate advanced
far to the north or to high elevations on the sea level. An example of such a case was provided by
N.G. Kolomiets (pers. comm.). In the southeast part of West Siberia, it is located the Barabinsk
Lowland. In it, there is a gradient of biomes from coniferous forests of the boreal type in the
north to steppe (grassland), and again forest biomes on slopes of the Altay Mountains in the
south. In the north and in the south, the grassland biome borders with the birch-aspen ForestSteppe biome. Here, it grows island stands, similar to those growing in the Western part of the
Western Siberia (the Chelyabinsk Region).
The latter were studied by P.M. Rafes and associates, who recorded here often and lasting
outbreaks of Porthetria dispar. Contrary, in the north part of the Barabinsk Lowland in birthaspen stands, Porthetria dispar is absent, whereas in the south, in the foothills of the Altay
Mountains, its outbreaks are common. N.G. Kolomiets explains this difference by an onset of
late frost over a season in the north and absence of the frost in the south.
In the mountain areas of a high elevation, late frost occurs over a season that excludes
outbreaks of Porthetria dispar. Such a situation takes place in the Plateau Ufa in Bashkiria
(Khanislamov et al., 1958, p. 17). Here, as in the lowland in Bashkiria, birch stands grow. In the
lowland, outbreaks of Porthetria dispar are common.
Thus, above examples demonstrate operation of CESPPs 2.3.5. "Onset of late frost over a
season." Its effect is 2.3.5.1. "Mortality in the diverse stages."
Contrary to Porthetria dispar, as to the rest of herbivores, available data about the role of
CESPPs 2.3."Routine weather suppression" are fragmentary. Nevertheless, these data are able to
demonstrate the important role of CESPPs 2.3. in maintenance of ESPPs on the level 3.1.
“Proper control.” Because diversity of traits in herbivore species is very wide, their density is
determined by great many weather situations.
The role of CESPPs 2.3. "Routine weather suppression" in restriction of activity of
Choristoneura fumiferana is significant in the Laurentide Park in Canada (Blais, 1965). This
park is situated on the high altitude – up to 4000 feet above sea level. Here, the season is usually
shorter than 60-80 days, late frost in spring is common, and cool summer unfavorable for the
budworm. J.R. Blais explains by these circumstances the less activity of the budworm in the
Laurentide Park than that on the low altitudes. If fact, in XX century, its outbreaks in the park
were less severe, and two vast outbreaks in other parts of Canada did not spread on the park.
In this case, it is possible an operation of the following CESPPs: 2.3.5."Onset of late frost
over a season" with the effect is 2.3.5.1. "Mortality in the diverse stages," 2.3.3. "Cool and
prolonged rains in the larval stage of defoliators" with the effect 2.3.3.1. "Mortality of larvae at
inducing of the acute form of infection" in cooperation with CESPPs 2.2.1. "Natural enemies of
invertebrate herbivores", 2.2.1.3. "Pathogens" (when decline at Low or Intermediate densities) or
CESPPs 2.5.3.1.4. "Mass mortality due to affection by acute form of infection and parasitization"
(when decline at High density).
A.I. Vorontsov (1978) considered causes of a decline of six successive outbreaks of the earlyspring guild of oak defoliators in the Moscow Region (Russia) from 1899 to 1974. Although in
all these cases, the severity of these winters was not too significant, the outbreaks were lasting,
so that affection of the populations with the slow form of infection was very probable. There are
the grounds to suppose that this phenomenon took place in the W.C. Cook’s zone (a).
105
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Above facts should be considered as operation of CESPPs 2.3.1. "Low ambient temperatures
at hibernation even if they are not extraordinary ones." Its effect is 2.3.1.1. "Unhatching after
hibernation." Because prolonged outbreak of defoliators are usually result in affection of the
slow form of infection, it is probable that in these cases CESPPs 2.3.1.1. operates in a
cooperation with the effect 2.5.3.1.5. "Spontaneous or winter mortality of embryos."
Here is an example of operation of CESPPs 2.3.2. "Weather stresses close to common (rains,
droughts, frost, etc.) in the period of development of post-embryo stages", 2.3.2.2. "Mortality
due to weakening by deficiency of food." in cooperation with 2.5.1. "Deterioration and/or
shortage of food." At High density of the larvae (density of the cockchafer, Melolontha
spp. sometimes reached seventy large grubs per square meter of the soil surface), they stay up to
the end of a season in an upper layer of the soil searching for food. Then, they die due to a
freezing out at winter frost (Sakharov, 1928). In this study, it was not recorded the extraordinary
frost. At plenty of food, the grubs in late summer penetrate in the soil depth, where they do not
suffer due to the frost.
One more example of operation of CESPPs 2.3.2.2. in cooperation with CESPPs 2.5.3.1.5.
"Spontaneous or winter mortality of embryos" has been provided by B.A. Areshnikov et al.
(1975). Overwintering adults of the sunn bug, Eurygaster integriceps Put. die on 70-80%, if their
weight is less 115 mg. It might be, the decrease of body’s weight was induced by affection of the
slow form of infection. These scholars did not suggest that severity of the winter influenced on
the mortality.
The both examples of CESPPs 2.3.2. are pertinent to the W.C. Cook’s zones (a) and (b).
Below it will be offered the cases of operation of the effect 2.3.2.3. "Mortality due to
affection by slow form of infection" at cooperation with CESPPs 2.5.3. "Increase of activity of
pathogens and parasites in the specific conditions of High host density" 2.5.3.1.3. "Mortality due
to weather stress and parasites."
In pupae of the noctuid moth, Pyrausta nubilalis Hbn., which died during hibernation, 91%
were affected with the microsporidia, whereas only 9% of the died pupae had no signs of the
infection (Issi, 1968). Furthermore, among these insects that died at spring drought, the number
of affected with the microsporidia pupae equaled 98%. This scholar cited other reports,
according to which the insects of diverse species affected with the microsporidia were able to
survive only at optimal environmental conditions. Even little deviations of the conditions from
the optimum led to high mortality.
R.S. Krasnitskaya and N.V. Lappa (1988) reported that in a result of treatment of larvae of
the fall webworm, Hyphantria cunea Drury with a preparation of the granulosis (Baculovirus),
mortality of the overwintering stage (pupae) increased, whereas pupal weight and fecundity of
the adults decreased.
CESPPs 2.3.2. "Weather stresses (rains, droughts, dews, etc) close to common in the period
of development of active stages" operating in a cooperation with CESPPs 2.2.1."Natural enemies
of invertebrate herbivores", 2.2.1.3. "Pathogens" or 2.5.3.1.4. "Mass mortality due to affection by
acute form of infection and parasitization" exert heavy suppression of sap-sucking arthropods.
E.G. Voronkova (1971) offered a review of literature and own data about affection of the pea
aphid, Acyrthosiphon pisum Harris by the entomophthoraceous fungus, Entomophthora
thaxteriana Petch. depending on moisture situation in the environment.
In areas, where summer rains are common (50-80 days with rains), the fungus keep density
of the aphid on very Low level continually. The same takes place in areas with common dew.
Presence of water drops in the media is necessary for activity of the fungi both at a spread of
their conidia by casting away an aphid body and at germination. When aphid density is High,
even short rain is able to induce mass mortality. At humidity of the media close to 100%, the
epizootics develop very quickly. A life cycle of the fungus continues only two-three days. Over a
single generation of the aphid (7-10 days), two-four generations of the fungus are confined to
this period. When aphid density becomes Low, transmission of the infection stops, and affection
by the fungus ceases.
106
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Depending on humidity of climate, E.G. Voronkova (1971) proposed a zonation of the
European part of USSR as to affection of the aphid by the fungus. The proposition is in an
agreement with the zonation by W.C. Cook (1929). Approximately, the zone (a) coincides with
the Steppe biome, the zone (b) - with the Forest-Steppe biome, and the zone (c) – with the Forest
biome.
Here is a case, which might be assumed as an example of 2.3.2. "Weather stresses (rains,
droughts, dews, etc.) close to common in the period of development of active stages." In
Ukraine, in the Forest-Steppe biome, density of the cereal aphid, Sitobion avenae F. on the
winter wheat is usually Insignificant or Low year after year, whereas in greenhouses, density of
this species reaches very High values – up to a thousand of the insects per wheat stem. Taking
into account the above data as to presence of drops of water on a plant surface as a prerequisite
of fungal activity, it is easily to explain continually High density of the aphids in greenhouses.
Neither rain, nor dew present here.
In studies by the author (Vasechko, 2001), the stems with the aphid were transferred from
greenhouses and exposed within a winter wheat field. Numerous attempts to spread samples of
the aphid on its host-plants outdoor failed. The exposed insects died off on open air, although
weather situation was not far from optimal for this species - worm and dry weather. The only
weather phenomenon, which might exert a suppressive effect on the aphid was dew.
The explanation of this supposition is the following. In a greenhouse, in the conditions of
absence of vectors of infection, the slow form of it is accumulated in an aphid population. Again,
E.G. Voronkova (1971, p. 780) pointed out not only acute epizootics of the entomophthoraceous
fungi, but chronic ones. In the field conditions, it presents an activator of the infection – dew,
which provides a spread of the pathogen that leads to explosion of the acute form of infection
within the exposed population. In this case, it operates CESPPs 2.3.2.1. " Mortality under effect
of the acute form of infection in the stages of larvae, pupae, and adults" in a cooperation with
CESPPs 2.5.3.1.4. "Mass mortality due to affection by the acute form of infection and
parasitization."
The tetranychid mites also suffer on the part of the entomophthoraceous fungi. J. Weiser
(1968) showed that colonies of the mites are affected, when they are under stress induced by
rains or unfavorable conditions at hibernation in some types of shelters. This report explains,
why the mites so numerous in greenhouses and at drought in open air.
A capacity of the autumnal moth, Oporinia autumnata Bkh. to reach High density depends
on a relief of a terrain. In the period of complete defoliation of birch stands by this species in
upper and intermediate stripes of valleys, the low stripes, especially in gulches stay intact
(Tenow, 1975). The absence of an infestation spot in the above conditions is explained by
inadequate microclimate – accumulation of cold air and weak insolation in lowlands. Thus, this
is an operation of CESPPs 2.3.4. "The sum of effective temperatures insufficient for completing
of a life cycle of a species." Its probable effect is 2.3.4.1. "Mortality in the pupal stage due too
low ambient temperatures."
Here are two situations, which might be considered as an operation of CESPPs 2.3.6. "Return
frost after thaw", 2.3.6.1. "Mortality of young larvae in eggs", in a cooperation with 2.5.3.1.5.
"Spontaneous or winter mortality of embryos" or independent.
N.N. Padiy (1974, p. 142) noted the cause of decline of outbreaks in the early-spring guild of
oak defoliators, particularly the green oak moth Tortryx viridana L., which consisted in a return
of frost after the lasting period of thaw. The latter provoked the embryos to develop, but the
severe returning frost (20°C below zero) killed them.
A similar phenomenon was observed by I.D. Povzun (1981). It took place heavy mortality of
embryos of the apple ermine moth, Hyponomeuta malinellus after a decrease of air temperatures
in March, when the embryos started to develop. In this population, the value of mortality was
checked after the period winter temperatures 29°C below zero. This value occurred to be
negligible. However, due to decrease in March of ambient temperature to 10.5ºC below zero, up
to 75% of embryos died.
107
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The health of the herbivore populations is unknown. This effect might be independent in its
action. It is probable cooperation with CESPPs 2.5.3.1.5. "Spontaneous or winter mortality of
embryos" that promotes activity of the action. The operation of CESPPs 2.3.6. "Return frost after
thaw" is possible in all the W.C. Cook’s zones.
On the other hand, hardness of a herbivore population to severe frost can be very high. Such
datum is available again for Hyponomeuta malinellus Zell. In winter 1963-1964 in the eastern
part of Ukraine, air temperature dropped to 32ºC below zero. Nevertheless, in spring of 1964,
95% of the embryos produced larvae (Degtyaryov, 1966a). Perhaps, this population was not
affected by the slow form of infection.
The ermine moth, Hyponomeuta cognatellus Hb. feeds by foliage of the prick-wood,
Evonimus europeus L. and E. verrucosus Scop. This defoliator produces a protective web net
covering the larval and pupal stages. The cover provides an effective protection against
entomophagous organisms only at dry weather. What is happened at rains, it has been described
by P.F. Kadochnikov (1938, cited in O.G. Kelus, 1940). When raining, the cover becomes wet
and heavy that results in a tearing it in pieces. Then predators (birds, predaceous insects) and
parasites gain access to the larvae and pupae, whereas pathogens affect the rest. Often, it is
observed a complete destruction of the population in an infestation spot at rains. It is stated that
even a little rain could bring a heavy damage to a population of the moth.
This report allows explanation, why outbreaks of this species are common in the Steppe
biome, where rains in the period of the larval and pupil stages are rather rare events. In more
humid areas, outbreaks of this species are realized only at droughts.
In above case, it is action of CESPPs 2.3.7. "Rains and dews in web-making defoliators" with
two effects, namely: 2.3.7.1. "Mortality under effect of parasites and predators due to disturbance
of a web cover by rains", and "2.3.7.2. "Mortality of larvae due to inducing of the acute form of
infection in the conditions of high humidity" in cooperation with CESPPs 2.5.3.1.4. "Mass
mortality due to affection by acute form infection and parasitization" or CESPPs 2.2.1."Natural
enemies of invertebrate herbivores" 2.2.1.3. "Pathogens."
The similar events one may observe in settlements in Ukraine, in particular in Kyiv on shade
trees – the apple-tree and stony fruit trees. They are usually affected by the ermine moths,
Hyponomeuta spp. At droughty weather, such trees are covered with a web of the moths. At
rainy weather, these species disappear. In settlements, an access of parasites is little of probable,
but activity of avian predators and pathogens is obvious.
One more example of the role CESPPs 2.3.7. "Rains and dews in web-making defoliators" is
the case of the fall webworm, Hyphantria cunea Drury in the Crimea Peninsula (Ukraine). This
species is common in the steppe areas of the Crimea, where significant rains from May to
October are rare. But in the southern coast of the Crimea, in particular in Yalta, this species is
unknown. Here, showers occur over all the season.
There is a situation, where the only effect 2.3.7.2. "Mortality of larvae due to inducing of the
acute form of infection in the conditions of high humidity" operates. This is the case of the
processionary moth, Thaumetopoea processiana L. This species is nearly absent in the LowDnieper area – a terrain of the flood plain, in contrast to Porthetria dispar, which is abundant
there (A.G. Kotenko, pers. comm.). The absence of the species might be explained by its traits to
pupate in a web cover in July- beginning of August. In this period, rains are absent, but dew is
common. On the secadol in southern areas, where in this period neither rains, nor dews take
place, Thaumetopoea processiana stays in appeciable density.
The brown-tail moth, Euproctis chrysorrhoea L., when invaded in North America, appeared
in mass numbers in the eastern coastal areas, and after not too long period, the moth nearly
disappeared. A probable cause of the disappearance is activity of introduced parasites that has
led to affection of its populations with pathogens. The web nets produced by larvae of this
species protect against birds, but in conditions of wet climate, the nets increase moisture in larval
media to values, which favor affection by pathogens. In addition, rains break the nets that
facilitate access of the parasites. In this case, it operates both the effects 2.3.7.1. and 2.3.7.2.
108
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The effect 2.3.7.1. is characteristic for the W.C. Cook’s zones (b) and (c), whereas the effect
2.3.7.2. – for the zones (b), (c), and (d).
The beet webworm, Loxostege sticticalis L. is common in grassy biomes of Europe and Asia.
Outbreaks of this species are limited by areas of moderate summer temperatures and humidity –
the Forest-Steppe and typical Steppe biomes (Shchegolev et al., 1949, pp. 357-358).
V.P. Pospelov (1934) found out in fat body and gonads of several species of butterflies some
inclusions, which were determined by this scholar as yeast symbionts. The inoculum from
spermatophores of males of the Loxostege sticticalis L., when grown on artificial media, gave the
culture of the hyphomicaetes similar to the fungus Endomyces spp. When in the flight period of
this species, it stays wet and cool weather, the spermatophores in females’ bodies were filled by
micelium and fruiting organs of this fungus. This led to degradation of egg tubes and early
mortality of the females. On the base of this fact, V.P. Pospelov explains, why outbreaks of
Loxostege sticticalis arise in the Steppe biome in East Europe and West Siberia, but they are
unknown in the areas to the north, where cool and wet weather situation is common in the flight
period of the first generation of the moth.
The similar inclusions were found out by V.P. Pospelov in Phytometre (Autographa) gamma
L., Feltia (Scotia) segetum Schiff., Manduca atropos L. , Vanessa polychloros L., and V. urticae
L. The inclusions, which were considered by this scholar as symbionts, were probably pathogens
staying in the slow form of infection.
This is an example of operation of CESPPs 2.3.8. "Cool and prolonged rains in a flight period
of moths." Its effect is 2.3.8.1. "Mortality of adults due to transformation of symbiotic (?)
microorganisms in pathogens." This effect is probable in the W.C. Cook’s zones (b), (c), and (d).
A deficiency of precipitation in the flight period also exerts a suppressive effect on density of
Loxostege sticticalis. Again,…"V.P. Pospelov found out that at high air temperature and
insignificant precipitation at mass flight of the moths, the females loss their fertility…. The
largest fertility is observed, when at mass flight amount of precipitation in millimeters is no less
than the number of grades of average temperature per 10-day period. Probably, the effect of
precipitation on the moths is indirect, and it is connected with a change in availability of nectar
feeding. For development of the embryos, it is necessary feeding of the females on flowers…As
it has showed tests by Skoblo (1933, 1935), not every feeding of the moths by solutions of sugars
is able to provide developments of the embryos. 10-20% sucrose solution impedes development
of the embryos, whereas the 25% solution stops the development and degeneration of unripe
ones. Glucose in such concentrations does not effect on the development. Taking into account
that depending on weather situation concentration of sugars in flower nectar fluctuates in the
range 20-70%, the changing of fecundity finds simple explanation" (Ivanov et al., 1938, pp. 135136).
Feeding by nectar is necessary for oviposition only in the moth with body weight less than 40
mg (Ibid., p. 135). A small body weight is characteristic for High density of a herbivore
population.
This effect might be considered as operation of CESPPs 2.3.9. "Drought at the flight periods
of moths in the species, which need in imaginal feeding." Its effect is 2.3.9.1. "Decrease of
fecundity of moths due to shortage of nectar" with participation of the effect 2.5.3.1.1. "Decrease
of fecundity."
The effect 2.3.9.1. " Decrease of fecundity of moths due to shortage of nectar " operates in
the case of the apple ermine moth, Hyponomeuta malinellus Zell. The females of this species
need in feeding, and their fecundity depends closely on availability of nectar. Dry and hot
weather during the flight period suppresses flowering and productivity of nectar. Therefore, at
such a weather situation, the fecundity is low (Degtyaryov, 1966a).
The effect 2.3.9.1. "Decrease of fecundity of moths due to shortage of nectar" operates in the
W.C. Cook’s zones (b), (c), and (d).
There exists a phenomenon, which until was not explained. The Siberian pine moth,
Dendrolimus sibiricus Tschetv. is a dangerous pest of forests in the Siberia. The range of
Dendrolimus sibiricus was shown on a map in the book by A.I. Il’insky and I.V. Tropin (1965,
109
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
p. 220). The range of this species spreads on the entire taiga Biome in East Europe and Siberia.
The problem is why its outbreaks are limited nearly by the territory of Asia. In Europe, its
outbreaks were recorded on a small area in the Volga Basin – the southern part of the Nizhiy
Novgorod Region (Russia). The limitation of a west border of the range by the Volga Basin is
strange, because host-trees of the moth are abundant in Europe. They are diverse coniferous
species. Outbreaks of this species are known in stands, where Antibiosis (CESPPs 2.1.1.2.1.) in
dominants is decreased. Such a situation is common in Europe. Mobility of its moths is
advanced. Nevertheless, there exists a hindrance for further expansion of this aggressive species.
An explanation of the phenomenon might be found in the report by A.C. Konikov (1966). He
has concluded: "…in the period of withdrawal to hibernation, a dry state of forest litter is one of
the main conditions of surviving of a population. It has been shown (Konikov et al., 1963) that
wet caterpillars of this species die at temperature below 3C below zero … The ecological range
of the Siberian pine moth embraces upland forest plots. In its evolutionary history, the Siberian
pine moth has formed as a component of the ecosystem of mountain coniferous taiga… On
mountain slopes, water does not linger"(Ibid., pp. 15-16).
A.I. Vorontsov (1958, p. 181) has paid attention on further environmental limitations of this
species, namely: "High mortality of the caterpillars is observed in the period of hibernation in
wet forest litter at early snow-fall or at numerous snow melting, when onset of thaws." This
factor can be a hindrance for spread of the range of Dendrolimus sibiricus in southwest direction
(in Europe). As to Siberia, thaws are not characteristic for climates of this area.
Indeed, this species thrives in the distinctly continental climate of the Siberia that provides it
by adequate conditions for hibernation. Contrary, more wet and worm climate of Europe
precludes possibility of presence of it in noticeable density, although its moths were traced in
northern forests up to the White Sea. In the Siberia, climate is naturally is unequal with a
gradient of increasing aridity from north to south. Correspondingly, the cited map shows four
belts extent from the west to the east, which reflect occurrence/abundance of Dendrolimus
sibiricus. These belts should be considered as four W.C. Cook’s zones. The zone (a) is situated
on extreme south of the range, whereas the zone (d) – on extreme north.
Outbreaks of this species arise after droughts, and areas affected by High density spreads
from most xeric habitats to more wet ones. Thus, an operation of CESPPs 2.3.10. "Unfavorable
conditions in sites of the dormancy period." Its effect is 2.3.10.1. "Mortality of larvae due to
excessive moisture content in sites of hibernation." The role of this CESPPs is essential in
maintenance of ESPPs to Dendrolimus sibiricus.
The effect 2.3.10.1. operates in the W.C. Cook’s zones (b), (c), and (d).
The same effect 2.3.10.1. "Mortality of larvae due to excessive moisture content in sites of
hibernation" is important for survivorship of the beet webworm, Loxostege sticticalis L. in
spring, when its larvae undergo histolysis preceding their pupation. In this period, the larvae are
especially susceptible to sharp changes of ambient temperatures. The susceptibility is determined
by moisture of the media, i.e. the soil, where the larvae hibernate. This is so because their
cocoons are easily penetrable for moisture. When the cocoons are saturated by moisture,
decrease of the temperature leads to freezing on the larvae that results in mortality of them. In
the environmental conditions, where spring is characteristic by dry weather, and the sandy-clay
soil is well permeable for water, density of the beet webworm is continually higher than that in
other areas of its range. Such a situation takes place in the Kalmyk Region (Russia) situated in
the Steppe biome in the Volga Basin. These facts were reported by L. Lozina-Lozinsky (1933,
cited in S.P. Ivanov et al., 1938). The Kalmyk Region is the W.C. Cook’s zone (a) for the L.
sticticalis.
In summer, the thripses, Thrips spp. often die in the nymphal stage due to over-drying of an
upper layer of the soil, where these insects find shelter (Dyadechko, 1964, pp. 246-274; and pers.
comm.). This is an operation of CESPPs 2.3.10. "Unfavorable conditions in sites of the
dormancy period." with the effect 2.3.10.2. "Mortality due to over-drying of the soil surface at
summer dormancy." This effect is possible in the W.C. Cook’s zones (b), (c), and (d).
110
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The discourse on the thripses should be continued. The fluctuations of density of the apple
blossom thrips, Thrips imaginis Bagnall on the rose in Australia provide ecologists with
knowledge of an indirect action of CESPPs 2.3. "Routine weather suppression." The study by J.
Davidson and H.G. Andrewartha (1948, 1948a) showed that the peak density of these insects
took place usually in the beginning of December, and it depended on air temperatures in
preceding months. Such effects of temperatures was clear: the temperatures determined an
amount of thrips’ food resource - blossoms of the roses.
In December, it came hot and dry weather situation, and after two months density of the
thrips decreased to very Low level. Such effect of air temperatures was poorly understood,
because food of the thrips (pollen of the rose’s flowers) was not exhausted, and, therefore, was
available to the insects.
The explanation of causes of the suppression excited controversy in scholars. Some of them
found out signs of action of the density-independent factors that was characteristic for
suppression due to weather phenomena (Andrewartha and Birch, 1964, Murray, 1979). Other
scholars insisted on the directly density-dependent, smooth action that was characteristic for the
factors concerned to food, rather than for weather ones (Kuenen, 1958; Smith, 1961; Varley et
al., 1975). Again, this was strange, because food of the thrips (the pollen) was consumed
incompletely, so that on the first glance the food resource was abundant in spite of the fact of
thrips’ suppression.
The issue becomes clear if to know that the pollen is not the only food of the thrips. These
insects need in nectar. The onset of high temperatures in December decreases producing of the
nectar. In the conditions of limited amount of nectar, the higher density of the thrips, the more
deficiency of the nectar. Therefore, mortality grows with an increase of the density that
determines the density-dependent, smooth pattern of mortality at the initial operation of weather
factors.
As to supposition about necessity nectar for feeding of this insect, it based on the fact that the
relatives of Thrips imaginis inhabiting Eurasia need both pollen and nectar. This is true for
various species including those feeding on the family Rosaceae (Dyadechko, 1964, pp. 246-274;
and pers. comm.). The food deficiency takes part in this effect, but it operates in a veil over form.
Thus, in the above case with Thrips imaginis, it takes place of operation CESPPs 2.3.11.
"Drought devastating food resource." with the effect 2.3.11.1. "Mortality due to starvation and at
emigration." If High density stimulates this behavior, it serves as a cooperator CESPPs 2.5.1.4.
"Emigration in the adult stage in advance of food deterioration of and/or exhaust" with the effect
2.5.1.4.1. "Mortality due to diverse factors."
Again, CESPPs 2.3.11. "Drought devastating food resource." with the effect 2.3.11.1.
"Mortality due to starvation and at emigration." operates in suppression of phytophagous mites at
heavy drought, when leaves of their host-trees become close to fading. Then, the mites disappear
due to emigration and mortality (A.N. Voytenko, pers. comm.).
The effect 2.3.11.1. is characteristic for the W. C. Cook’s zone (b).
As to Mayetiola destructor, it is known that an important limitation of its density is posed by
diapausation of its pupae that decreases the number of its generations per season, and probably
enhances its mortality. It has been assumed that the diapausation is caused by drought in the
period of pupation (Shchegolev et al., 1949, p. 387). This is an operation of CESPPs 2.3.12.
"Drought in the pupal stage" with the effect "2.3.12.1. Decrease of polyvoltinism and increased
mortality due to diapausation over the long period."
The term of an onset of drought exerts great impact on population dynamics of this species.
A.F. Kryshtal (1974, p. 505) supposes that drought in the period of pupation of the first
generation increases the number of a population, because it stays in diapause to fall avoiding
mortality due to deficiency of the vulnerable stage of host-plants. In fall, the flies colonize
abundant tillers of winter cereal crops. Contrary, drought in the period after pupation of the first
generation decreases the density.
According to the studies by R.H. Painter (1958, p. 277) in Kansas, the role of weather factor
in population dynamics of Mayetiola destructor is close to that of host-plant Antibiosis. In fact:
111
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
"Since 1948 the weather was unfavourable for the development of this insect. Under the
combination of unfavourable weather and resistant varieties the Hessian fly population has
decreased to the point where it has been almost impossible to find any evidence of the insect
even in the most favourable locations. With the return of weather more favourable to the fly this
level of resistant acreage (ten to fifty per cent) may not be sufficient to keep down the fly
population."
The effect 2.3.12.1. "Decrease of polyvoltinism and increased mortality due to diapausation
over the long period" is possible in the W.C. Cook’s zones (b) and (c).
The population dynamics of the grey larch budworm, Zeiraphera diniana (grizeana) in the
Engadin Valley (Switzerland) provides us by good examples of the important role of two
subcategories of CESPPs 2.3. "Routine weather suppression."
In fact, L.R. Clark et al. (1967, p. 128) have given the following scenario of impact of
climate on this species: "The most favourable temperature regime for overwintering in the egg
stage and the establishment of larvae in the spring occurs at altitudes of 4,800 to 6,000 ft. Below
4,800 ft, earlier springs and warmer summers cause many eggs to hatch in the autumn instead of
during the spring, and others die after an exceedingly long preconditioning phase at relatively
high temperatures. The survival of the remaining individuals is jeopardized by poor synchrony
between hatching in the spring and the production of new foliage by larch. Above 6,000 ft, the
prevailing temperatures remain too low for too long to allow timely diapause development. At
altitudes of 4,800 to 6,000 ft, population trends in Z. griseana appear to be affected very little
variation in weather – even by extreme conditions (Auer, 1961)."
Retelling this report in the terms used in the present publication, it should say that on the
altitude below 4,800 ft, the budworm is suppressed by CESPPs 2.3.13. "The sum of effective
temperatures, which exceeds of demands of a species" with the effect 2.3.13.1. "Mortality in the
egg stage due to impossibility of diapausation at high temperatures in fall."
Contrary, on the altitude above 6,000 ft, it operates CESPPs 2.3.4. "The sum of effective
temperatures insufficient for completing of a life cycle of a species" with the effect 2.3.4.2.
"Mortality in the egg stage due to impossibility of diapausation at low temperatures in fall."
The efficacy of these CESPPs is illustrated well by population dynamics of the budworm in
the altitudes 4,800 – 6,000 ft, where they do not operate, and where "nowhere else, however, do
its number show that strict oscillatory pattern recorded in the Upper Engadine where maxima
and minima are reached throughout the area at intervals of seven to ten years" (Clark et al., 1967,
p. 124).
Here, weather situation continually precludes the operation of CESPPs 2.3."Routine weather
suppression", and CESPPs 2.1.1.4.1. "Evasion from herbivores." Therefore, ESPPs (of the level
3.3. "Late control") is maintained by a cooperation with CESPPs 2.1.1.3.1.2. "Tolerance to
herbivores, Repair or compensation of losses of host-plant tissues" and CESPPs 2.5. "Effects of
crowding."
The effect 2.3.13.1. "Mortality in the egg stage due to impossibility of diapausation at high
temperatures in fall" is characteristic for the W.C. Cook’s zones (c), and (d), whereas the effect
2.3.4.2. "Mortality in the egg stage due to impossibility of diapausation at low temperatures in
fall" – for the zone (d).
Here is the case of the important role of CESPPs 2.3.14. "Enhancing of CESPPs 2.1."Plant
resistance to PPs" with the effect of 2.3.14.1. "Mortality due to enhancing of host-plant
antibiosis." It has been known the situations, where ESPPs to the Hessian fly, Mayetiola
destructor is maintained by certain weather situation. This is the case of the varieties Arthur 71
and Abe. R.H. Painter (1958) has showen that Antibiosis in these varieties to the fly is
temperature-dependent. This trait operates, when air temperatures stay at 15°C. that keeps the
number of affected plants on the value 3%, whereas at temperature 27°C, the number reaches
97%.
O.Sosa Jr. and J.Foster (1976) found out that the same is true for most of studied by they
varieties of the winter wheat, and recommended to evaluate resistance of this crop against
112
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Mayetiola destructor at air temperature more 27°C. These CESPPs operate in cooperation with
2.1.1.2.1. "Antibiosis to herbivores."
The effect 2.3.14.1. "Mortality due to enhancing of host-plant antibiosis" is characteristic for
the W.C. Cook’s zone (b).
CESPPs 2.3.14. " Enhancing of CESPPs 2.1. Plant resistance to PPs" with the effect of
2.3.14.2. "Mortality due to enhancing of host-plant evasion" in maintenance of ESPPs is
provided by the interrelations between the English oak, Quercus robur L. and the green oak
tortrix, Tortrix viridana L.
The host-tree of Tortrix viridana the English oak is a species with trees of the phenological
forms having different terms of bud-bursting. The interval between the forms with the earliest
term and the latest one reaches a month. There exist oak trees with the intermediate terms of
bud-bursting.
Studies by W. Thalenhorst (1951) and F. Schütte (1957,1957a) have showed that density of
Tortrix viridana is determined by the success in a temporal coincidence of the larval hatching
and the bud-opening. In turn, these terms depend on weather situation. Thus, early spring after
severe winter promotes the early hatching and the late bud-bursting, because oak roots stay a
long time being inactive in the frozen soil. On the other hand, when mild winter is followed by
cool spring, the bud-bursting leaves takes place before the hatching.
When the larvae hatch at fully closed oak buds, they die due to starvation. Then, the effect
2.3.14.2. operates in a cooperation with CESPPs 2.1.1.4.1.1. "Starvation (exposition on
2.1.1.2.1.1.1.)." When the larvae hatch at the fully open buds (after the phase of "a green cone"),
they have no shelter in buds, they feed openly and suffer from affection by natural enemies. In
such cases, the effect 2.3.14.2. "Mortality due to enhancing of host-plant evasion" operates in a
cooperation with CESPPs 2.1.1.4.1.2."Evasion from herbivores, Exposition to 2.2.1." The larvae
are affected mainly by parasites.
The potent effect 2.3.14.2. operates rather rarely, density of Tortrix viridana and its satellites
is significant every season, so that all the range of the early-spring guild of oak defoliators
should be attributed as the W.C. Cook’s zone (a).
The circumstances, where it operates CESPPs 2.3.15. "Inability to feed under effect of
weather stress in vertebrate herbivores" with the effect 2.3.15.1. "Mortality due to starvation and
decrease of fecundity" will be considered in the next chapter – CESPPs 2.4. "Periodic (bottleneck) suppression."
The role of weather factors in maintenance of ESPPs of the level 3.1. “Proper control” to
phytopathogens becomes clear, when weather situations provoke epiphytoties. S.A.J. Tarr (1972,
Ch. XX) noted that even a little change of a single meteorological factor can be of the crucial
role, especially there exists an exact balance between a phytopathogen and its host-plant. The
practice showed reliability of forecasts of population dynamics of phytopathogens on the base of
recording weather data. The classical example is the forecast of situations with Phytophthora
infestans on the potato in the Netherlands, the British Isles and the USA.
Also, the forecasts showed the comparative role of host-plant resistance and aggressiveness
of a phytopathogen. The forecast is valid on condition that growing of susceptible varieties and
the aggressiveness is high. In such circumstances, there are no obstacles for an epiphytoties. This
fact implies the priority of interrelations between a host-plant and a phytopathogen, rather than
weather at to severity of affection.
The role of weather factors has been shown well by P.E. Waggoner (1968) and W.H. Hogg
(1970).
Consider the role of CESPPs 2.3.16. "Enhancing of CESPPs 2.1.1.2.2. "Antibiosis to
phytopathogens" with the effect 2.3.16.1. "Insusceptibility to phytopathogens."
Antibiosis of the winter wheat to the leaf rust is also temperature-dependent. The varieties,
which maintained their Antibiosis to this phytopathogen over many years, suddenly lost this trait
in the seasons with sharp skip of weather situation from cold spring to hot summer. "…in Belaya
Tserkov, such years were 1953 and 1955. In these years, it took place the loss of resistance in all
the varieties, which had it before. In 1953, affection of the winter wheat by the leaf rust was so
113
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
sudden and intensive that over four-five days the entire leaf surface became dry. In 1953 and
1955, spring was cold and wet. In June, air temperature for 24-hour period sharply increased to
20.3°C, whereas precipitation sharply decreased" (Gorlach, 1958, p. 147).
The weather-dependent expression of Antibiosis to phytopathogens was recorded by
S.L Tyuterev (1981) in the Cruciferous agricultural crops: Brassica napobrassica, B. napus, var.
rapifers, and B. oleracea, var. capitata. The studies were conducted in the Neva Lowland, the
Leningrad Region (Russia). In some seasons, at the definite weather situation in the period of
mass appearance of plantlets, it took place inducing of their Antibiosis to Plasmodiophora
brassicae Wor. In B. oleracea, var. capitata, the developed Antibiosis remained only in the
seedling stage. In the two former crops, it was retained up to maturity.
COMPONENTS of ECOSYSTEM STABILITY to PLANT PESTS of the CATEGORY 2.4.
PERIODIC (BOTTLE-NECK) SUPPRESSION
2.4.1. Mortality and/or reducing of fecundity due to deficiency of vital resources
in vertebrate herbivores active over all the year
There are great many remarkable cases, which illustrate an importance of this phenomenon as
CESPPs. In the book by P. Farb (undated), it was reported that before the invading of Europeans
in North America, huge herds of the plain bisons, Bison bison bison wandered on the prairies.
The number of these animals is evaluated to be 60 million individuals. Nevertheless, the prairies
were covered by luxuriant vegetation. What kinds of the factors prevented the growth of bison’s
density to the amount, at which the vegetation would be destroyed? Such a problem indeed
exists, because the degradation is common, when people let domesticated hoofed animals to
forage without limitation.
P. Farb (undated) proposed the following explanation of absence of the destructive effects of
the bisons on the prairie ecosystem: herds of wolves run after continually the bisons consuming a
part of the youngsters and weakened old-aged animals. However, a validity of such a suggestion
is doubtful. Indeed, Ph. Mowat (1963) showed that wolves were unable to limit density even of
the caribou, Rangifer tarandus L., i.e. much more weak animals than the bisons. Naturally, the
same is true for such mighty animals as bisons. The problem of the stability of the prairie
ecosystem as to grazing by bisons still is open.
The solution of this problem can be found, when considering the interrelations between
hoofed animals and vegetation in African savanna described in the book by J. Dorst (1965). The
equilibrium existing here long since becomes broken if people start to promote these animals
providing them with watering in a dry season making ponds. Being survived in a dry season
without significant losses, these animals reach the density, at which they consume nearly all the
vegetation in the savanna. This process is called "desertification." It is common also at grazing of
livestock with watering and additional feeding in a dry season.
These facts suggest that ESPPs of the level 3.1. "Proper control" in the savanna ecosystems to
hoofed animals is maintained by existence just the severe seasons, when density of the animals
decreases. In such a season, the animals suffer due to deficiency of water and food. In a result,
they become weakened, and their mortality grows under impact mainly of predators, if people
have not suppressed the latter. In the dry season, grassy plants survive in the inaccessible for
herbivores state (seeds, subterranean parts of the plants). When favorable season returns, grassy
plants restore their activity, whereas density of the herbivores stays below a threshold of damage
for dominants.
Just for such a situation, it is appropriate to use the figurative expression "a bottle-neck
effect."
In the areas of temperate climate, the same effect is exerted by a winter season. The examples
of importance of these factors are numberless. In hunting enterprises, the additional feeding of
animals both mammals and birds is organized just in winter that promotes to growth of density
of these animals. High winter mortality of the titmice was noted by Ch. Darwin. In text-books,
114
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
the additional feeding of the titmice in winter is a common recommendation of the biological
method of pest insect control.
A number of data related to this issue one may find in the book by S.A. Severtsev (1941).
This scholar operated information about population dynamics of the auroches (European wood
buffalo), Bison bonasus L. for nearly a whole century – from 1806 up to 1902. These data were
obtained in the Belovezhskaya Pushcha – the last reserve of this species in Europe in XIX
century. In the second part of that century, it was organized an additional feeding of the auroches
in winter. In a result, the progeny of the auroches became to appear annually, whereas without
the additional feeding, a single calf was born in two years. In summer, the auroches did not
interest by food stored for them (stacks of hay). They began to come to the stacks in fall and fed
by the hay up to spring.
In this excellent book, it has been also reported about population dynamics of the squirrel,
Sciurus vulgaris L. that is valuable for understanding of nature of ESPPs to this seed-consuming
species. A density of the squirrels varies rather regularly depending on a yield of seeds of
coniferous species. In accordance with the yield, the maximal density takes place approximately
every seventh season in the north parts of East Europe and West Siberia with the wide range of
oscillation, whereas in south of Siberia it occurs every second-third season with a less amplitude.
The deficiency of the seeds exerts its effect just in winter. Mortality is not the main result of the
deficiency. Although in the years with very low seed yield, the squirrels died due to starvation
are found often in early spring, the main stock of these animals survives using for feeding lichens
and fruit bodies of wood-destroying fungi. The effect of the winter food deficiency mainly
consists in suppression of fecundity of the squirrel. S.A. Severtsev (1941, p. 148) has noted that
the number of younglings per brood, the number of broods per season, and the terms of the
squirrels’ heat depend on availability of food in winter. This factor determines fat resource of a
squirrel’s body.
The combination of low seed yield with severe season leads to the situation, when in a season
the abundant seed yield, density of the squirrel occurs not so high to consume all the seeds. Thus,
ESPPs of the level 3.1. "Proper control" to the squirrels is maintained by a cooperation of
CESPPs 2.4.1."Mortality and/or reducing of fecundity due to deficiency of vital resources (in
vertebrate herbivores active over all the year)", and CESPPs 2.1.2.2.1. "Disappearance from
herbivores." The role of squirel’s predators is secondary one.
The role of CESPPs 2.4.1. as a suppressor of density of the reindeer, Rangifer tarandus L. in
the Tundra biome becomes clear by studies of A.S. Leopold and F.F. Darling (1953, cited in
C.S. Elton, 1958); F.F. Darling and A.S. Leopold (1953, cited in A. MacFadyen, 1963).
According to these reports, the introduction of the reindeer in Alaska led to intensive growth of
its density, because the predators (the wolves) were destroyed. Further, the population
abandoned traditional nomad behavior. In a result, its density locally increased greatly, that was
followed by a sharp decrease of the density due to starvation and affection by pathogens. The
initial cause of the decrease consisted in an exhaust of the winter food of these animals – the
lichens.
Consider the winter food of hoofed animals in areas of temperate climate. Here is the report
on the sitka deer, Cervus nippon introduced in the Voronezh Region (Russia) presented by
L.F. Arens (1944). In winter, these animals feed by the sedge, Carex pillosa Scop., which
overwinters as a green plant. The yield of green mass of the sedge per hectare is evaluated by the
above scholar as close to 100 kg. This value is far less than the yield of green mass of a mediocre
pasture per season. The grass productivity of a good pasture is 20 times as much. The food value
of the sedge is low. Therefore, in a worm period of year, the deers having a choice disregard the
sedge. In addition, in winter, the deers feed by the lichens on tree stems. Obviously, the food
resource of the deer in winter is very limited.
Here is one more example of the suppressive effect of winter food deficiency on hoofed
animals. This is the pony in the Sable Island in the Atlantic Ocean. Due to the lack of predators,
an availability of food is probably the only limited factor in their population dynamics. Their
density is determined by amount of winter food that depends on weather situation. After
115
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
particularly severe winters, their density drops nearly twice comparing with that after weather
situation in winter close to normal one. During several successive years after severe winters,
their fecundity is low.
Thus, ESPPs of the level 3.1. "Proper control" of the Sable Island ecosystem to the pony is
maintained by a cooperation of CESPPs 2.4.1. "Mortality and/or reducing of fecundity due to
deficiency of vital resources (in vertebrate herbivores active over all the year)" and 2.3.15.
"Inability to feed under effect of weather stress in vertebrate herbivores" with the effect 2.3.15.1.
"Mortality due to starvation and decrease of fecundity."
A cooperation of the same CESPPs maintains ESPPs of savanna to the African elephant,
Loxodonta africana, var. africana. Climate of this ecosystem is characterized by presence of
a dry season, when these animals suffer from water deficiency. It is especially dangerous the
drought within the season that sometime onsets with intervals of a number of years. The water
deficiency forces the elephants to migrate in search for watering places. In so doing, they need to
wander across open areas. These obstacles place them, in particular younglings, in a difficult
position, often resulted in the sunstroke (Sikes, 1966, 1971; Field and Laws, 1970, cited in A.A.
Nasimovich, 1975). It was noted that at severe drought, the elephants needed to walk over 80 km
per 24 hours. This way is beyond the strength of lactating females and younglings (Darling,
1964: Laws, 1970, cited in A.A. Nasimovich, 1975).
Although heavy droughts occur with intervals of a number of years, they are sufficiently
frequent to restrict of population growth of a species, which was characterized by Ch. Darwin as
"the slowest breeder of all known animals."
When people want to help animals in winter, it is need to overcome an operation of 2.4.1.
"Mortality and/or reducing of fecundity due to deficiency of vital resources (in vertebrate
herbivores active over all the year)." Thus, winter 2000-2001 in the USA occurred to be severe.
The bisons in reserves began to starve. Therefore, they were maintained by forage.
2.4.2. Mortality or weakening under a direct effect of weather stress
in herbivores, which spend a severe period both in active and inactive state
In insect herbivores, this CESPPs operates by means of mortality of a part of a population
during a severe season of a year. This part embraces individuals weakened under effect of
diverse factors. In particular, they are individuals, which have developed in the conditions of
shortage of food or of inadequate food. Therefore, their body weight is low. If a severe season
would absent, such weakened individuals would survive resulting in increased density of
herbivores.
The evaluations of density of insect herbivores before hibernation and after that at any levels
of their density show that in spring, the density is lower. When the density in fall is High, winter
mortality is especially high. Nevertheless, winter mortality is sometimes significant at the
Intermediate and Low densities. Therefore, CESPPs 2.4.2. operates as a cooperator of CESPPs
2.5. "Effects of crowding", and as an independent CESPPs.
The obvious cause of the increased winter mortality is also weakening due to affection of the
inapparent form of infection. The above cited data by I.V. Issi (1968) and R.S. Krasnitskaya and
N.V. Lappa (1988) about mortality of overwintering stages of lepidopterous insects affected by
pathogens suggest the important effect of the infection.
In vertebrate herbivores, it is known the effect of severe conditions of overwintering on a
subsequent affection of a population by pathogens and increased mortality. The examples of
such phenomena are offered in particular by N.P. Naumov (1963). Concerning to the vole,
Microtus brandtii, and the tarbagan, Marmota sibirica, this scholar reported that affection of
them with low-virulent strains of the Pasteurellosis was common, but it did not exert an
appreciable harm to them, whereas in summer after severe winter and late onset of spring, their
mortality due to this pathogen became high (Ibid., pp. 503-504).
116
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
In Norway, at late spring, when snow cover precluded an access to berries, it was spread
mass mortality of the partridge (three species), the heath-cock, the wood-grouse, and the hazelhen due to affection with the Coccobacillus, Eimeria avium (Brinksman, 1926, Closter, 1928,
Hordhagen, 1929, cited in N.P. Naumov, 1963, p. 508).
In temperate climate, vertebrate predators of diverse families come in heat at the end of winter,
when their preys (vertebrate herbivores) are weakened by winter stresses.
2.4.3. The effect of severe season in the context of host-plant evasion
In climatic conditions with a severe season, there are the periods, when development of
agricultural crops is possible, whereas activity of herbivores and phytopathogens is suppressed.
Understanding of this phenomenon has opened the prospects to use these periods at agricultural
practice to decrease affection by PPs. That is the winter method of crop cultivation. In so doing,
a crop is sown in fall in the dates, when weather conditions are admissible for development of
them, whereas they are suppressive for activity of PPs. The crops keep their vitality in winter,
and in the next spring are able to begin their development so early that their vulnerable stages are
completed before activity of PPs becomes significant after winter depression.
The most expressive example of the advantage of this method is the case of the winter wheat
as to protection of it against the cereal flies, especially the Mayetiola destructor, and
phytopathogens – leaf diseases and root rots.
According to this method, for protection of the winter wheat against the Mayetiola
destructor, it was found out the dates of sowing in the wide range of climates, i.e. depending on
the latitude of a territory. H.T. Fernald (1926, p. 316) recommended to do the sowing in the
beginning of September in northern regions (North Michigan) and in the first half of November
in south (the Georgia State). The validity of this recommendation has been proved by its usage
until now. In particular, this measure is sufficient for protection of the crop in New York State
(Cox, 1987).
This fact demonstrates potency of CESPPs 2.4.3. "The effect of severe season in the context
of host-plant evasion." Nevertheless, it should pay attention that it is absolutely effective in the
areas, where a severe season of a year is well expressed. On the other hand, in the southeastern
USA, the sowing date does not give valid protection against the Mayetiola destructor, because
the local climate allows development a generation of this species in winter (Johnson et al., 1996).
Although this generation is non-numerous, an increase of pest density in spring outruns
appearing of invulnerable stages of the wheat. Therefore, the serious damage of the wheat is
possible.
The case of a lack of operation of CESPPs A.2.1.2.1.1. "Superevasion from herbivores" on
the winter wheat as to Mayetiola destructor in south of the USA shows, why at presence of a
severe season, density of herbivores and aggressiveness of phytopathogens are always less that
those in the areas with the conditions favorable for these PPs over a year. The better conditions
of development of PPs over a year, the greater realization of their SP, in particular the number of
generations per year. In the areas with such a climate, it is need to practice other measures of
plant protection.
117
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
COMPONENTS of ECOSYSTEM STABILITY to PLANT PESTS 2.5. "EFFECTS of
CROWDING" ENTERING into OPERATION
at CROWDING of HERBIVORE or PHYTOPATHOGEN POPULATIONS
2.5.1. Deterioration and/or shortage of food
2.5.1.1.Raising of secondary evasion
2.5.1.1.1. Delayed bud-bursting (exposition on 2.1.1.2.1.1.1.)
2.5.1.1.1.1. Starvation
On next year after heavy defoliation by the grey larch budworm, Zeiraphera diniana Guenee,
bud-bursting is delayed that results in a lack of coincidence of it with hatching of the budworm
larvae (Benz, 1976). In a result, the neonate larvae cannot feed on closed buds of host-trees.
This effect causes of mortality of that part of a population, which has not migrated from an
infestation spot. Probably they are weakened insects, which unable to migrate. They die due to
starvation.
2.5.1. Deterioration and/or shortage of food
2.5.1.2. Raising of secondary structural antibiosis
2.5.1.2.1. Exuding of protective substances on a surface of buds or developing of protective
barriers in affected tissues
2.5.1.2.1.1. Starvation
Due to repeated defoliation of Zeiraphera diniana, on surface of buds it appeared a thick
layer of oleoresin (Baltensweiler et al., 1977). This is a serious obstacle for neonate larvae of the
budworm at their attempt to penetrate into the buds for feeding. In a result, the larvae die due to
starvation.
At High density of balsam wooly adelgid, Adelges (Dreyfusia) piceae Ratz. on the fir Abies
alba Mill., cells in phloem of these trees die converting into a thick and hard layer, which
precludes feeding by the insects forcing them to leave attacked trees. In a deeper part of the
stems, it arises a new cambium layer, so that vital activity on the trees is not disturbed. These
findings were reported by J. Franz (1956), W. Kloft (1957), H. Karafiat and J. Franz (1965).
The same effect is known in the grape at increasing of density of Phylloxera spp. B.A. Rubin
et al. (1975, pp. 155-156) citing A.S. Kiskin (1966) reported that in root bark of resistant to this
pest grape varieties, feeding by Phylloxera induced formation of the wound periderm, which
isolated sound tissues from affected ones. This periderm consisted of 5-15 layers of died cells,
which was filled by suberine. Contrary, in susceptible grape varieties, the periderm consisted of
only 3-5 layers of such cells. The thick wound periderm not only suppressed the adelgid’s
feeding, but also laid obstacles for penetrating of soil fungi and microbes into affected roots. It
seems, the latter is the main advantage of the periderm.
R.Baur et al. (1991) reported about a formation of structures of the protective concern on
leaves of the gray alder, Alnus incana L. as a result of damage by the chrysomelid beetle,
Agelastica alni L. In this tree species, at heavy feeding by the beetle, it arose new foliage with
greater density of trichomes than that in unaffected trees. At high density of trichomes, the
females did not lay their eggs on leaves and left the trees. The protective role of the trichomes
was proved by an experiment.
The phenomena of this category take place at heavy grazing by livestock on young forest
trees. Young trees (in the seedling and sapling stages), especially being grown in open areas
(pastures) often lose their terminal and side sprouts with tiny bark and young foliage due to
grazing. The response of such trees consists in a lengthening of lower branches and formation of
on their ends short and entangled twigs. In so doing, it arises a rather kind of rigid brush that
grows in all the sides surrounding the terminal. This structure has a common name "a skirt." It is
118
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
a little suitable for feeding by cattle. When it becomes so spacious to protect the terminals from
cattle’s muzzles, the trees begin grow up.
In all the above cases, it takes place the sequence of effects – 2.5.1.2. – 2.5.1.2.1. – the final
effect 2.5.1.2.1.1. "Starvation."
2.5.1. Deterioration and/or shortage of food
2.5.1.3. Raising of secondary physiological (biochemical) antibiosis
2.5.1.3.1. Appearing in endangered tissue of protective substance or
increase of their content
2.5.1.3.1.1. Suppression of vitality or mortality
An increase of protective substances in a response on defoliation is probable in the host-plant
species having Antibiosis at healthy state.
Needles of the larch contain oleoresin, which, however, does not preclude defoliation at
proper physiological state of the trees. G. Benz (1974), who noted that healthy larches offer the
best conditions for feeding of Zeiraphera diniana, reported that in result of repeated defoliation
of larches, content of oleoresin sometimes increased.
T.G. Vasil’yeva and A.S. Pleshanov (1972) compared content of probable protective
substances in needles of intact larches and in the trees affected by Zeiraphera diniana, including
the secondary needles. The samples were taken in May, June, July, and August in a season of
defoliation. The content oleoresin, tannins, polyphenols and extractive substances as the whole in
calculation on dry weight of tissue was actually the same in all the variance; in the next season
(in June) the results were similar (Ibid., pp. 33-35).
This problem of response of the larch on defoliation was studied concerning the Siberian pine
moth, Dendrolimus sibiricus by A.S. Rozhkov (1965). He attached importance to changed
chemical composition of secondary needles (repaired in the same season needles) of the larch in
suppression of Dendrolimus sibiricus, and considered the changes as a protective traits in areas,
where outbreaks of this species were common (Ibid., p. 68). In this context, A.S. Rozhkov put
the question as to a probable increase of content of oleoresin in the secondary needles.
Nevertheless, his analyses did not confirm this supposition. At calculation on dry weight, in the
secondary needles, concentration of oleoresin was indeed greater. But because content of
moisture in the secondary needles was much higher, concentration of oleoresin on total weight in
the secondary needles was less than that in the primary ones (Ibid., pp. 67-68).
In the context of considering effects, it should touch on the hypothesis of the distant effects
of trees affected herbivores on their neighbors. This hypothesis was rather popular in 1970-1980.
Its essence has been well-expressed by J.H. Myers and K.S. Williams (1984, p. 74), namely:
"…it has been suggested by Rhoades (1983) and Baldwin and Schultsz (1983) that insect
herbivores not only induce the production of the "secondary" chemicals in trees on which they
are feeding, but that attacked trees communicate with unattacked trees in the same vicinity (60
m) to stimulate protective chemicals production in these trees as well."
As to the communication within a tree population directed on inducing of Antibiosis in
neighbor trees, the validity of this suggestion is very doubtful that has been noted in particular by
P.G. Wratten (1985).
Also, it was reported about protective effects of damage by defoliators on adjacent leaves.
E. Haukioja and T.Hakala (1975 and subsequent publications with co-authors) studied the
impact of defoliation of the mountain birch, Betula pubescence spp. tortuosa by the autumnal
looper, Oporinia autumnata Bkh. or the simulation of damage by its larvae on vitality of this
insect. The scholars (Haukioja and Hakala (1976, p. 44) stated that "… the growth is retarded in
the larvae of a geometrid moth (Oporinia autumnata) if they feed on (undamaged) leaves whose
adjacent leaves were, however, damaged mechanically two days earlier, or, if they eat leaves of
trees that were defoliated one or two years earlier." Rearing of the larvae on detached birch
leaves increased weight of the pupae (Ibid., p. 45). Rearing of larvae of this species and two
119
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
others on intact birch leaves collected near by damaged leaves resulted in decrease of pupal
weight and increase of mortality of the larvae (Haukioja and Niemela, 1979).
These findings suggest an absence of protective substances in leaves of healthy host-trees and
appearing of such substances in a result of damage of the trees by defoliation or cutting of their
roots. As to the nature of the protective substances, it was supposed accumulation of phenolic
ones. Their content in birch leaves increased at diverse damaging impacts. They are inhibitors of
tripsine, a ferment splitting host-tree proteins. The deficiency of tripsine in a herbivore organism
retards its growth.
From the standpoint of ESPPs, it is important that the response of the host-trees on damage
by the defoliators does not preclude growth of their density resulting in heavy and repeated
defoliation. As to explanation of a decline of these outbreaks, there exist other factors, which
exert much more significant effect on a herbivore population than the small decrease in the
indices in above studies. If damage of a leaf at the feeding would significantly suppress the
larvae consuming neighbor leaves, density of the defoliators hardly would reach High values.
Summing up, there are no valid data as to the effect 2.5.1.3.1. "Appearing in endangered
tissues of protective substances or increase of their content" indeed takes place, and it exerts
significant effect on herbivores, which was suggested as 2.5.1.3.1.1."Suppression of vitality or
mortality."
2.5.1. Deterioration and/or shortage of food
2.5.1.3. Raising of secondary physiological (biochemical) antibiosis
2.5.1.3.2. Deficiency in endangered tissues of nutrients and increase of worthless stuff
in host-plant tissues
2.5.1.3.2.1. Weakening due to bad feeding
An exhaust of stores of nutrients in plants in a result of heavy defoliation of them is obvious,
as well as a restoration of the stores throw several years if affected host-plants have survived.
Therefore, this phenomenon concerning tree foliage is used widely for explanation of
fluctuations of defoliator’s density. In particular, from this standpoint, P.M. Rafes (1980, p. 165)
explained population dynamics of Porthetria dispar in the south-west part of the West Siberia
(the Chelyabinsk Region, Russia). Indeed, in this area, outbreaks of Porthetria dispar are regular
with heavy defoliation over two-three seasons and recurrence of the outbreak in a few years.
As an additional factor of the population dynamics P.M. Rafes proposed fluctuations of
content of protective substances in foliage of host-trees. Nevertheless, any data as to content of
nutrients in context of these studies have not been known. Again, it has no data about a presence
of protective substances in foliage of the host-plants (the birch).
A.I. Vorontzov (1978, p. 111) supposed that deterioration of food quality of oak foliage
served as a cause of a decline of outbreaks of the green oak moth, Tortrix viridana L. However,
he did not present any factual data.
A number studies make this problem clear. Thus, G.H. Heichel and N.G. Turner (1976)
revealed a little effects of defoliation by Porthetria dispar on content of nutrients in oak foliage.
The removal of leaves that simulated feeding by Porthetria dispar over three seasons in
succession resulted in the following: a moderate decrease of starch and reduced sugars at 59%
leaf removal, as well as a weak decrease of content of these substances at 75% and 100% leaf
removal. At the last operation, the content of sucrose even became higher. It was important that
content of nitrogen was not changed at defoliation of all the intensities.
The important study was conducted by J.H. Meyers and K.S. William (1984) with the
western tent caterpillar, Malacosoma californicum pluviale Dyer on the red alder, Alnus rubra
Bong. They found out that heavy defoliation over three seasons in succession led to a weak
decrease of some indices of vital activity of this insect. Only the decrease of pupal weight
occurred to be significant. The weak defoliation over three seasons or heavy defoliation in a
current season and preceding one did not influence on all the studied indices.
120
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
These schorars noted the factor, which can induce mistakes at conclusions as to effects of
defoliation. A source of the mistakes consists in an affection of a herbivore population with
pathogens, which grows simultaneously with the progression of an outbreak. The degradation of
a population affected by the inapparent form of infection and the high mortality as a result of
a bursting of a disease at arising of the acute form of infection can be took for the effect of food
deterioration in a result of defoliation.
Another set of data reported about the pronounced effect of crowding on food quality of food
and vitality in defoliators.
A.S. Rozhkov (1965, pp. 66-68) compared content of nutrients in the primary needles of the
larch and secondary ones in the context with feeding of Dendrolimus sibiricus. It was stated that
in the secondary needles content all the nutrients on the total weight decreased. The decrease was
especially significant as to hydrocarbons and proteins – approximately in twice, whereas content
of moisture occurred to be increased. The deterioration of food was destructive for the larvae of
the first and second instars, which are forced to feed by the secondary needles in fall. They
cannot amass in their organisms a necessary store of nutrients, and die either in fall or at
hibernation. This suggestion is based on his observation of mortality of the young larvae at the
first morning frost in fall in 1958. At normal feeding, such a frost is insignificant for the larvae.
The response of the larch on heavy defoliation is considered by this scholar as a protective
trait, which limits the period of complete defoliation of the larch by only two years.
Nevertheless, Dendrolimus sibiricus is able in some conditions to overcome this trait by a
lengthening of its development on three seasons. Is so doing, the feeding is less intensive, so that
the larch has time to repair its needles. Then, the heavy, but not complete defoliation of the larch
continues three-four years in succession.
At a decline of outbreaks of Zeiraphera diniana, it decreased the content of protein, whereas
content of cellulose (the worthless stuff) increased (Benz, 1976).
On the next year after heavy defoliation of the larch by Zeiraphera diniana in Siberia,
content of total nitrogen, protein and non-protein nitrogen in needles decreased in two-three
times (Vasil’yeva and Pleshanov, 1972, pp. 30-31). In so doing, the content of monosugars,
disugars, and starch did not change.
The effects of defoliation were studied in the brown-tale moth, Euproctis chrysorrhoea L.
This case is provided by R.V. Naumov (1959). He has shown that complete defoliation in
summer forces the larvae to feed by repaired foliage in fall. The young foliage has a lot of
proteins, but a little of sugars that is unfavorable for this species, because it promotes growth of
the larvae, but puts obstacles for preparing of them to hibernation. In a result, winter mortality of
the larvae increases from 12% to 60%.
The effect of food deficiency is known well in vertebrate herbivores. This is a distress,
decrease of progeny and voltinis (the number generations per year). In the rodents, it was studied
the phenomenon of "dissolving" of embryos, which was defined as "embryonic mortality"
(Severtsov, 1941, pp. 147 - 152).
At very low yield of seeds of coniferous trees, the squirrels, Sciurus vulgaris L. were forced
to feed in winter by mycothalluses (Polyporus spp.) and lichens. Then, in spring, it was often
found squirrels died due to starvation; the survived animals were very exhausted, they pared
lately and produced a little brood (Ibid.p. 148).
When the final effect 2.5.1.3.2.1. "Weakening due to bad feeding" of 2.5.1.3.2. "Deficiency
of nutrients and increase of worthless stuff in host-plant tissues" is potent, CESPPs 2.3. "Routine
weather suppression" is able to exert further suppressive effect on a herbivore population. This
effect is referred to as CESPPs 2.3.2.2. "Mortality due to weakening by deficiency of food."
121
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.5.1. Deterioration and/or shortage of food
2.5.1.3. Raising of secondary physiological (biochemical) antibiosis
2.5.1.3.2. Deficiency in endangered tissues of nutrients and
increase of worthless stuff in host-plant tissues
2.5.1.3.2.2. Decrease of body weight and fecundity
A number of studies showed the effect of decrease of body weight and fecundity in
defoliators depending on the rate of food consumption, in particular concerning Porthetria
dispar. The first study, it seemed, was conducted by M.M. Levitt (1934). He stated that within
the range of female pupae weight 700 – 1250 mg (nine weight groups), the average fecundity
increased from 288 to 487 eggs.
This scholar studied female pupal weight and fecundity at three gradations of consumption of
host-tree leaves – 5-10%, 50% and 90-100% of total amount. The average pupal weight was
1250 mg, 1150 mg, and 700 mg, whereas fecundity was 487; 320, and 288 eggs, respectively.
D.F. Rudnev (1936, 1951) studied this dependence in the wider range of female pupal weight
(300 – 1900 mg), and calculated that an increase of the weight on 1 mg corresponded to growth
of the fecundity on 0.379+/-0.007 eggs. Moreover, the pupal weight exerted an influence on
weight of an egg of this species. At an increase of the pupal weight on 100 mg, average weight
of an egg increased on 0.270+/-0.003 mg.
Percentage of consumption of foliage influences on fecundity of defoliators in the same
generation of them. This dependence was shown by A.I. Il’insky (1932) for Panolis flammea
Schiff. S.P. Ivanov et al. (1938, p. 62) described this as follows: "Illinsky (1932), at study of
characteristics of pupae of the pine beauty moth in infestation spots of diverse age and density
found out wide variability of pupal sizes, and simultaneously fecundity (in place and time);
dependence of weight of the pupa on the level of damage of pine needles by the larvae, stated
that at an increase of consumption of the needle on 1%, average weight of the female pupae
decreased on 1.34 mg, correspondingly the fecundity of the moth decreased on 1.29 eggs per
1 mg of pupal weight. Thus, an increase of the damage leads to decrease of fecundity that is one
of causes of decline of moth density in future."
It might be the cause of the above dependence consists in the fact that nutritive value of
tissue within a leaf is unequal. At Low density, larvae of defoliators are able to choose most
valuables of them. Contrary, at High density, the are forced to feed by badly nourishing leaf
veins and stalks. These parts of a leaf contain high percentage of worthless stuff.
M.M. Levitt (1934) showed that consumption of 90-100% of foliage by larvae of Porthetria
dispar led to significant decrease of values of pupal body weight and fecundity. Direct starvation
was absent, but food had obviously worse quality.
At crowding, needle-eating defoliators are forced to consume those parts of needles, which
are rich of oleoresin ducts. Oleoresin effects negatively on vitality of defoliators.
2.5.1. Deterioration and/or shortage of food
2.5.1.4. Emigration in the adult stage
in advance of food deterioration or exhaust
2.5.1.4.1. Mortality due to diverse factors
A.S. Pleshanov (1972, p. 25) has supposed that Zeiraphera. diniata responds on deficiency of
nutrients by means of emigration from the ecosystems with heavy defoliation. "…the grey larch
moth does not affect two years in succession the same trees. As an obstacle of this, it serves a
retarding of terms of bud-bursting on the larches defoliated in a preceding year, and the change
of biochemical composition in these trees. The annual migrations of moths characteristic for this
insect in new stands are absolutely an adaptive trait – a means to evade from the conditions
122
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
unfavorable for development of the larvae in affected forest stands." The same conclusion was
done in the book by A.S. Pleshanov (1982, p. 183).
The migrations (emigrations of moths from stands with heavy defoliation) stop an outbreak
in a given forest plot, but the outbreak continues in the area-wide scale. Nevertheless, the
emigrations contribute in decrease of overall density of this species. The flying moths often are
turned up by the wing very high, and are got out in the baleful conditions. Pilots observed the
flocks of the moths on the height 900-1400 meters above sea level, and planes flew throw the
flocks during 4-5 minutes (Shabunevich, 1967). It was recorded a mass perish of the moths on
ices in the Eastern-Siberian Sea in 300 km from the coast (Andriyashev, 1947).
There exists the difference in behavior between populations of Zeiraphera diniana in the
Engadin Valley (Switzerland) and in Siberia. In the former, in the locality 1700-2000 meters
altitude, heavy defoliation by the moth continues several seasons in succession at intervals close
to seven-eight years. This population is able to emigrate – individuals of the "strong" type
migrate from the "early" locations to the "late" locations (Clark et al., 1967, p. 135).
Nevertheless, such emigrations are unable to preclude complete defoliation of host-trees over
several seasons.
On the other hand, in Siberia, this species exerts heavy defoliation only over a single season.
"…infestation spots have more or less expressed migrate character. In so doing, it takes place
annually displacement of zones of the damage by the grey larch moth, and the trees in the
infestation spots undergo only one-fold defoliation…" (Pleshanov, 1972, p. 19).
The difference in population behavior of Zeiraphera diniana might be explained by the fact
that High density of this species in Alps is a phenomenon known on not too large area.
Therefore, this population has had a limited evolutionary experience of evading from High
density. In Siberia, however, the outbreaks have arisen long since and spread on vast areas. Thus,
the outbreaks were begun to record from 1856 (Sel’ky, 1858; Frolov, 1961). They occur "…with
intervals 5-10 years and continue 2-4 years" (Pleshanov, 1972, p. 19). "…in 1966-1969,
infestation spots of the grey larch moth occupied about 70 million hectares of larch forests…"
(Ibid., p. 11).
In Asia, both sexes of Porthetria dispar have capacity to fly on large distance, so that they
leave their infestation spots in the adult stage (Baranchikov and Kravtsov, 1981). The possibility
to survive is obviously greater if the emigration from infestation spots with High density is
proceeded in the adult stage than that in the larval stage. This difference in this respect among
the Asian populations and ones in Europe as well as in America gives ground to suppose that this
is connected with evolutionary experience of diverse populations of the species.
The European populations have been formed in the conditions of large tracts of mesophytic
forest, where outbreaks of this species hardly to be common. The trend of their evolution is a
maximal fecundity that correlates with a reduction of a capacity to fly in the females. The shortdistant flight of the females is not a disadvantage, because the passive spread of the neonate
larvae by the wind within tracts of forest gives good chance for finding of host-trees. Affection
by parasites and pathogens of the populations staying of Low level of density was moderate.
Therefore, there was no need in urgent emigrations.
Unlike, the Asian populations have evolved in the xerophytic conditions of island forest
plots, where outbreaks have been common long since. Here, emigrations of the populations are
necessary for getting put from heavy affection by parasites and pathogens in the outbreak phase,
as well as at food shortage. Further, the emigrations should be directed, because it is of crucial
importance for the population to come into an island forest, rather than into vast tree-less areas
surrounding these forest plots. An undirected dispersion in the larval stage would lead to mass
mortality of the populations, which unable to feed by grassy vegetation. A flight of fecundated
females solves the problem of a shift of forest plots. Of course, the distant flight leads to
significant mortality, but such mortality is less than that in a collapsed population at decline of
infestation spot. The effect of the emigration is referred to as 2.5.1.4.1. "Mortality due to diverse
factors."
123
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
In nowadays, in Europe, forest conditions have been changed, so that outbreaks of Porthetria
dispar have become common. The inability of the females to fly in native populations of
Porthetria dispar results in a retention of High larval density within an ecosystem. This forces
the larvae to emigrate in late instars due to starvation. These traits of European populations of
Porthetria dispar are kept in America.
In some species of owlet moths (the family Noctuidae), butterflies are able to migrate en
masse on the distance of hundreds or thousands km. As aims of such migrations are supposed to
be not only search of food for progeny, but also to evade from shortage of vitamin E in nectar in
sites of emergence of these insects. Such habits are known for Chloridea peltigera Schiff., Ch.
nubigera H.-S., Mythimna loreyi Dup., Spodoptera exigua Hb., Autographa gamma L. and
others (Klyuchko, 1974).
A maximal expression of traits of migration as a means to evade from decrease of food
quality, starvation and natural enemies is known in insects with nomad behavior – the locusts
and aphids.
If density of larvae of the Asiatic locust, Locusta migratoria L. exceeds some value, the
adults hatch as having traits of the horde phase in spite of the larvae are supplied by food in
abundance (Uvarov, 1927). For transition of rearing insects of this species from the solitary to
horde phases, it is sufficient to get the larvae some visual or tactile stimuli (Chauven, 1956).
Such a transition takes place if the solitary larvae are placed side by side under a glass dome on
the light.
"Clark (1949) observed that the formation of marching bands of young hoppers (Chortoicetes
terminifera) and mass emigration from feeding ground occurred while there was still plenty of
food available to the individual present…Without mass emigration scarcely any individuals
could have obtained enough food to reach adult stage" (Clark et al., 1967, p. 55).
In the aphids, the response on an increase of density, H.F. van Emden (1972, p. 271) has
described by the following words: "…the production of of alate progeny on both winter and
summer hosts is produced by overcrowding stimuli (van Emden et al., 1969) following a rapid
succession of parthenogenetic generations to apterous vivaparous females."
The final effect 2.5.1.4.1. "Mortality due to diverse factors"’operates also in vertebrate
herbivores. Here is an example concerning the rodents.
N.P. Naumov (1963, pp. 372-379) reported that at plenty of food, diverse groups of the
rodents (mice, voles, ground squirrels, hamsters) forage within such a distance around their
burrows, where they have time to run to a burrow at an attacks of predators. Contrary, at
shortage of food, the rodents are forced to move away from a burrow on the distance, at which a
predator is able to catch them. Moreover, starving rodents used to leave their burrows and search
for the areas with food. In so doing, they carry the young, which sometimes still blind and
hairless.
In the period of starvation, the same behavior is common in carnivorous animals – foxes,
polar foxes, and wolves. They carry their cubs sometimes on several km.
The squirrels Sciurus vulgaris L. in years with low yield of their food (tree seeds and nuts)
emigrate from their family plots before exhaust of their winter stores. N.P. Naumov (1963,
p. 372 citing A.N. Formozov, 1936) has supposed that this is a good tactics, because the
migration proceeds, when the animals are well fed and at rather favorable weather situation, and
they are stopped at onset of frost. At the migrations, a significant part of the squirrels dies, but
the rest finds the plots with sufficient food.
To summing, the effect 2.5.1.4. "Emigration in the adult stage in advance of food exhaust" is
expressed unevenly in diverse taxa of herbivores, and it depends on evolutionary experience of a
taxon. Those taxa, which long since reached often High density, have had advanced traits of
emigration from infestation spots, where exhaust of food resource is possible.
The advanced expression allows decrease negative effect of consumption of host-plants, and
mortality of herbivores at migrations so that both counteracting organisms (plants – herbivores)
are in a gain.
124
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.5.1. Deterioration and/or shortage of food
2.5.1.5. Migration in the larval stage with leaving of shelters in some species
2.5.1.5.1. Mortality due to diverse factors
L.R. Clark et al. (1967, pp. 132-133, citing W. Baltensweiler, 1958) have reported about
Zeiraphera diniana the following: "As numbers rise, intraspecific competition intensifies
sufficiently to compel larvae to forage widely, thus increasing their exposure to a variety of
hazards…Parasites lay…their eggs on…individuals which are either fully exposed or partly
covered by protective webbing, e.g. when the are foraging."
Larvae of Tortrix viridana having abundant food spend all the time under a web cover in
host-tree crowns and pupate here being well-protected against parasites and predators. However,
the larvae of an overcrowded (starving) population are forced to leave their shelters. When they
wander on the soil surface, carabid beetles consume them en masse (Schütte, 1957a).
In the same situation, the great numbers of larvae of this species are eaten by the ants. An
amount of preys of an anthill of the genus Formica is evaluated to be close to 100 thousand of
the larvae per day (Dlussky, 1967, p. 167).
The spectacular migrations of starving larvae of a number species known in Europe and
North America probably are caused by the lack of more advanced trait to migrate in the adult
stage. The owlet moths and defoliators of the pine can reach High density only in last centuries,
when it appeared large areas of monocultures – agricultural crops and badly managed forest
stands.
In some species of the family Noctuidae (the owlet moths), the migrations are so common
that they are called "army worms." In particular, as to Cirphis unipuncta Haw. "…all the food
where these insects are, may have been consumed if the larvae are abundant, and in this case
they march off in armies to find new feeding grounds…" (Fernald, 1926, p. 276). The same is
true concerning the fall army worm, Laphygma frugiperda S. & A. (Ibid., p. 277).
In Europe, the migrations were observed in outbreaks of the turnip moth, Scotia segetum
Schiff., the cabbage noctuid moth, Mamestra brassicae L., the beauty moth, Panolis flammea
Schiff. It was recorded emigration from completely stripped forest stands larval bands of the
European pine moth, Dendrolimus pini, and the gypsy moth, Porthetria dispar. As to the latter
species, it was described the case, when masses of the larvae covered railroad on the distance a
mile that made a hindrance for transport.
Here is a case provided by I. Zhikharev (1928, p. 299). In 1895, at a sublime outbreak of
Porthetria dispar in Russia, its larvae and larvae of the lackey moth, Malacosoma neustria L.
defoliated completely 200 ha of beautiful oak forests in the Fastiv forestry unit near by Kyiv.
Then, the larvae moved from the defoliated part of the unit to intact one. In so doing, they
covered a railroad on the distance of 1 km. In a result, trains had to stop.
A stopping of trains due to covering of a railroad by moving Porthetria dispar larvae was
noted by F. Keppen (1883 p. 62).
Even more expressed migration activity of Porthetria dispar larvae was recorded in America.
Consider the report by F.H. Forbush and C.H. Fernald (1896). This species penetrated in
America in 1868 or 1869, but up to 1890, it was unnoticed. Beginning with 1890, it became a
true distress for people in towns of New England devouring foliage all the plants and causing
public nuisance. The parasites, which in that time were only native species, exerted insignificant
mortality. Neither avian predators, nor ground (mammal) ones attacked its significantly. Activity
of pathogens was not noticeable.
That was a situation, when all the natural enemies are unable to prevent growth of a
herbivore population up to a limit of its food resource. Therefore, the only factor, which stops the
growth, is mortality due to starvation, if artificial control measures are not practiced.
Now such a situation can arise in the advancing front of the generally infested area and in the
island infestations in North America. In these areas, the expanding population of Porthetria
dispar occurs out of touch with most part of its natural enemies. The subsequences of
insignificant activity on natural enemies were lividly described by R.W. Campbell (1974, p. 18)
125
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
in southern New Jersey in 1972 soon after Porthetria dispar had invaded into this area:
"…ground …resembled a moving carpet – a carpet composed of starving caterpillars."
2.5.1. Deterioration and/or shortage of food
2.5.1.6. Wounding of insect herbivores at contacts
2.5.1.6.1. Weakening
2.5.1.6.1.1. Mortality due to natural enemies
An operation of these effects is common in herbivores, whose progeny develops in a closed
space. This effect is a cause of decrease of density of stem borers being predetermined by
availability of host objects – phloem and sapwood of trees, which are devoid of CESPPs
2.1.1.2.1.2. "Antibiosis to herbivores, Physiological (biochemical)."
Shortage and/or deterioration of this resource results in operation of the sequence of effects –
2.5.1.6. – 2.5.1.6.1. – 2.5.1.6.1.1. "Mortality due to natural enemies." In the condition of
overcrowding, wounded at contacts insects are affected by pathogens. The character of feeding
by carnivorous organisms raises doubt. They are rather saprophagous organisms than predators.
This issue will be considered later in the Section 5(1) Bark beetles, Coleoptera: Scolytidae.
2.5.1. Deterioration and/or shortage of food
2.5.1.7. Cannibalism
2.5.1.7.1. Direct mortality
An operation of these is also common in herbivores, whose progeny develops in closed space
(Fox, 1975).
The classical example of the important role of cannibalism in population dynamics of
a species is provided by flour beetles (Tribolium spp.). This phenomenon impedes consumption
of food resource in a closed space, and, therefore, maintains a population until it appears
a possibility to go out.
Stem borers are suspected to be cannibals to decrease competition among larvae, when their
density is High. Because the interrelations are difficult for observations, this issue is still open.
V.D.Ogievsky (1909) reported about cannibalism in the cockchafer, Melolontha melolonta L.
He has observed that the larvae of fourth of fifth year (in this species, a generation continues four
or five years) ate the first-year larvae, and intensity of the eating depended on availability of
food, i.e. roots, for the old larvae.
This trait serves as a cause of the periodicity in a flight period of the cockchafer. An
abundant flight of this species takes place every fifth of fourth years. This is so because those
larvae have the best chance for survivorship, whose the first year of life falls in a season of the
mass flight period, when the soil is free from the old larvae. This scholar also observed an eating
by the old larvae insects of other species.
The same behavior was recorded in diverse species of the soil-dwelling guild (Coleoptera Scarabeidae, Elateridae).
The leaf-rollers (Lepidoptera, Tortricidae) dwell inside fruits or in web nets. P.W. Geier
(1961, cited in L. R. Clark et al., 1967, p. 75) reported that butterflies of the codling moth, Cidia
(Carpocapsa) pomonella L. often lay several eggs in an apple germ. If this apple grows as a little
one, only single larva survives, whereas the rest are killed due to cannibalism. In a large apple,
several larvae are able to survive.
Cannibalism is considered as wide spread mechanism of regulation of density in noctuid
moth, the family Noctuidae (Schweitzer, 1979). This is a means of survivorship of a population
in a stress situation without loss of potency reproduction. The report is notable by the statement
that expression of cannibalism varies widely even within a genus. Thus, within the genus
Lithophane, in L. querquera, cannibalism is developed, whereas in L. semiusta and two other
species, it does not arise at any crowding.
126
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Again, if several caterpillars of the oak leaf roller, Tortricodes tortricella Hb. are placed into
a closed vessel, only a single larva survived, whereas the rest occur to be eaten up
(V.T. Dyachuk, pers. comm.).
Cannibalism was recorded in larvae of the European wheat stem sawfly, Cephus pygmaeus L.
and the black grain stem sawfly, Cephus tabidus F., when more than one eggs were laid in a stem
of the wheat (Udine, 1941). Such a behavior is necessary, because a wheat stem is able to
provide by food only a single larva of these species.
The behavior of larvae of insect parasites shows that they kill competitors, but do not eat
them. I.Ya. Shevyryov (1912, p. 46) placed eggs of hymenopterous parasites on water surface in
a laboratory, and saw as the firstly-hatched larva swam to the secondly-hatched one and killed it.
The former did not attempt to eat the latter.
The same behavior was demonstrated by C. Dupuis (1963) by examination of insect host
bodies. Here, it was found died and wounded larvae of parasites due to an attack of a competitor.
The firstly-hatched larva had advance in the competition.
2.5.1. Deterioration and/or shortage of food
2.5.1.8. Diapausation
2.5.1.8.1. Mortality under effect of natural enemies
Diapausation in the larval stage is studied well in seed-consuming insects (Stadnitsky et al.,
1975, p. 19) and the sawflies (Hymenoptera, Tenthredinidae) (Kolomiets et al., 1972). This
phenomenon consists in that a significant part of a population stays in inactive state during the
long period. In particular, up to a half of population of the European pine sawfly, Neodiprion
sertifer Geoff. is able to be inactive during four years (Ibid., pp. 103, 125). This trait is
considered as a protective one aimed on survivorship of a herbivore population in the conditions
of shortage of foodstuff. This role is obvious taking into account the periodical profound
decrease of foodstuff of seed-consuming insects.
Mass emergence of a sawfly population from diapause occurs after drought that decreases
Antibiosis (oleoresin exudation) in host-trees (Ibid., p. 18). Also, M.M. Zavada (pers. comm.)
supposes that diapausation of the pine sawflies is a response on increased oleoresin exudation in
pine needles at an onset of wet weather situation. Then, a sawfly population waits until drought
will return again.
Diapausation of pine sawflies allows to part of their populations to evade from the virus
infection (Kolomiets et al., 1972, p. 103).
The inactive state of insects over several years does not protect coccons against consuming
by predators. Heavy mortality of cocoons of the sawflies affecting coniferous trees due to
predation by the rodents is well known. Just a lack of such a predation is one of causes of often
outbreaks of sawflies in young pine monocultures planted on the dry sandy soils with the
insignificant forest litter. These soils are unfit for digging of the burrows, and the rodents do not
have in the plantations a stable food resource.
N.G. Kolomiets et al. (1972, pp. 56-105) offered a review of literature on the issue of
mortality during diapausation in forest litter. They concluded that mammal predation is the main
mortality factor in Europe, whereas in Pinus sibirica forests of Siberia the main role is played by
the parasite Pleolophus basizonus Grav., and the secondary role – by the rodent predator Sorex
araneus L. Larvae of the parasite also are able to stay in diapausation over four years. In a result
of activity of these entomophagous organisms, a sawfly population emerges from diapause being
significantly decreased. Nevertheless, this decrease is much less than if a population would stay
in active state until exhaust of food resource.
G.I. Sokolov (1987) reported about complete consumption of pupae in a number of
lepidopterous species within colonies of the common vole, Microtus arvalis over the term of
diapausation in the Chelyabinsk Region (Russia). This concerns Phalera bucephala L.,
Leucodonta bicoloria Schiff., Mimas tiliae L. and others, which spend several years in forest
litter. Outside of the colonies, most part of the pupae survives.
127
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.5.1. Deterioration and/or shortage of food
2.5.1.8. Diapausation
2.5.1.8.2. Disappearing of defoliators on the period,
which provides a reprieve for restoring of vitality of dominants
In the large pine sawfly, Diprion pini L., the most part of its population turned in
diapausation on the Intermediate level of density, so that defoliation did not exceed 60%
(Kharlashina, 1984, p. 12). Over three subsequent seasons, defoliation was kept on the level 26%. Such a damage was tolerable for dominant and codominant trees. Overall tree mortality for
the outbreak in the diverse affected stands was in the range 11.8-47.8% (Ibid., p. 10). Because
the outbreaks took place in overstocked pine plantations, such values of tree mortality are
favorable for survivorship of the stands.
This report suggests that diapausation is beneficial both for a sawfly population and its hosttrees. Indeed, several seasons after entering most part of this population into diapause are
sufficient for restoration of vitality of the dominants. Again, this is beneficial for the sawfly,
because its host-trees survived. A less part of them died. They were weakened by competition
within of stock of dominants before defoliation. The latter enhanced mortality of them.
Therefore, the rest of dominants occurred in better conditions to grow, so that, a diapausation
harmonizes interrelations between the defoliators and their host-plants.
2.5.1. Deterioration and/or shortage of food
2.5.1.9. Wounding at aggressive territorial behavior
2.5.1.9.1. Weakening
2.5.1.9.1.1. Mortality due to predators
The arising of intraspecific competition (aggressiveness) in the wide range of vertebrate
herbivores is known as a means of solving the contradiction between increased demand to food
at growth of species density and decreased availability of this food (Wynne-Edwards, 1965). In a
result, a winner in the competition gains sufficient food and, therefore, the good prospects on
establishing of its progeny. Contrary, the prospects of the vanquished are bad. They suffer due to
wounds obtained at the fights and subsequent starvation being impossible to resist predators.
To illustrate this suggestion, here is report about destiny of males, which have been defeated
in the struggle for a leadership in a herd. The appropriate data for the reindeer, Rangifer tarandus
have been offered by O.I. Semyonov-Tyan-Shansky (1948, p. 65). He reported that such males
composed the main part of a wolf’s plunder. Participation of the males reached 85% of all the
preys. In a result, a sex ratio (males : females) in a reindeer population was 26% : 74%.
Experimental studies of this problem have shown that territorial behavior limits population
density in birds and fishes (for review see R.H. Hinde, 1970, Ch. 28).
2.5.1. Deterioration and/or shortage of food
2.5.1.10. Decrease of body weight at shortage of food and/or
forced feeding by inadequate food
2.5.1.10.1. Decrease of fecundity and increase of mortality due to weather stress
These effects are obvious. Therefore, it is not need in search for the case stories in literature.
Rather that some facts shown in the present Section might be considered as concerned to this
category.
128
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.5.1. Deterioration and/or shortage of food
2.5.1.11. Dormancy in vertebrate herbivotes
2.5.1.11.1. Decrease of body weight and fecundity
B.D. Abaturov and G.V. Kuznetsov (1983, pp. 60, 61 and 64) reported that the ground
squirrels, Citellus sp. at deficiency of food fell in dormancy, whose duration depended on
availability of food. They consumed no much than 20% of grass biomass in seasons with normal
moistening and up to 38% of it at drought. The prolonged dormancy decreased weight of the
animals and their fecundity.
2.5.2. Attraction of predators and parasites, increase of their searching activity
2.5.2.1. Mortality under effect of predators and parasites
An appearing of abundant vertebrate and invertebrate predators in infestation spots of insect
herbivores is well known. Wandering flocks of birds are able to clean from defoliators an
infestation spot of a little area. F. Friderichs (1930, Ch. 19) reported that carabid beetles flew
together into an infestation spot of Porthetria dispar from surrounding areas. A.G. Kotento (pers.
comm.) observed high activity of sarcophagid flies in the same conditions. They bit Porthetria
dispar larvae in flight. At an absence of increased density of Porthetria dispar, these flies limited
their activity by open areas, where they attacked cattle.
As to insect parasites, it is probable an aggregation to arising infestation spots of tachinid
flies. They are leaders among the parasites, which pursue a spreading population of Porthtria
dispar in the advancing front of the generally infested area in America.
The hymenopteral parasites, especially tiny species, are weak fliers. They hardly to be able to
direct themselves in arising infestation spots outside of their native ecosystems. A penetration of
the parasites into them is probably occurs by chance. Contrary, within of native ecosystems,
insect parasites are supposed to prefer a host species with increasing density.
C.C. Varley et al. (1975, Ch. 4) have posed the idea that the parasites are able to switch their
activity on most abundant host species. This is a resemblance of the "search image" behavior
discovered by L. Tinbergen (1960) in avian predators. This phenomenon is important for
maintenance of ESPPs, because entomophagous organisms concentrate their activity on
abundant species of herbivores and leave in piece scanty species of them.
2.5.3. Increase activity of pathogens and parasites in the specific conditions of high density
2.5.3.1. Ever-increasing accumulation in populations of the inapparent form of infection
resulting in decrease of body weight
There are numerous reports as to great changes in herbivore populations during their
population dynamics. In the beginning of the outbreak phase, insects have large size (weight),
high fecundity, low percentage of disease incidences, dark color, and they become nearly
omnipresent. The latter means that they are visible in any ecosystem with their host-plants,
although their High density does not take place everywhere.
It is obviously that in such cases a herbivore population undergoes the burst of vitality that
leads to arising of an outbreak in those ecosystems, whose ESPPs to a given herbivore species
has been decreased. This phenomenon, as well as a depression of a herbivore population at a
decline of an outbreak, when backward changes take place, have been known for a long time.
The changes in herbivore populations in a course of population dynamics have drawn attention
of many scholars. Nevertheless, this problem continues to be open.
In this Section, it will be made an attempt to consider available data on the phenomena in the
context of ESPPs. In fact, the phenomena take place in ecosystems on the level ESPPs 3.3. "Late
control", and they are determined by operation of CESPPs 2.5. "Effects of crowding." Therefore,
it is a hope that understanding of what maintains the level 3.3. "Late control" will make things
clear in population dynamics of herbivores. Thus, the province of population ecology is
129
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
prospective for understanding of ESPPs, whereas the latter is able to bring the same in the
former.
In the explanation of processes in the course of population dynamics, there exist two lines of
thinking. The first one suspects that the observed phenomena are a consequence of changes of
proportion of indivuduals with the hereditary load within populations.
This view is expressed clearly by J. Franz (1949). The concept is understood by the author of
this report as follows. On the eve of an outbreak, it arises conditions for a significant decrease of
pressure of natural selection in a herbivore population. Therefore, it reproduces intensively. In a
result, it takes place the inbreeding. In turn, it leads to wide hereditary variability, so that lethal
and semilethal genes become abundant within a population. Short period of a tempestuous
reproduction transfers into a decline, when a population becomes weakened due to its hereditary
load, because the defective genes accumulate in it. The suppressive effect of external hostile
factors (overcrowding, predators, and shortage of food) is secondary one.
N. Turner (1960, p. 689) has set forth the concept of J. Franz without any mention about
natural enemies, as follows: "….Franz (1949) suggests that outbreaks start because of relaxation
of normally rigorous natural selection. This is favourable for hereditary defective individuals
which would usually not survive. These multiply, and recessive segregate. When normal
rigorous selection acts again, mortality is very high and outbreaks collapses…outbreaks of
insects may collapse as a result of outbreeding."
It is rather strange however to suppose that amass of organisms having worse heredity (with
lethal and semilethal genes, with segregated recessives) produces the explosion of vitality of a
population as it takes place necessarily at beginning of its outbreak.
L.C. Cole (1958) and N. Turner (1960) have suggested that the possible cause of a
Porthetria dispar outbreak is a spontaneous crossbreeding among isolated inbreeding
populations. Hence, an outbreak is a mere chance.
Here is one more view on causes of fluctuations in herbivore densities that was recalled by D.
Pimental (1961, p. 65): "E.B. Ford (1930 and 1931) was the first to point out the importance of
genetic changes in population fluctuations. He proposed that "numerical increase inevitably
prepares the way for reduction, and reverse"…During mass increases caused by the changing
environment variability increases, and many inferior genetic types result."… "These are
eliminated, and the numbers reduced when conditions become more rigorous again (Ford,
1956)."
The second line in the explanation suggests interrelations of a herbivore population with its
natural enemies as the main causes of the changes in a process of population dynamics, and
character of the interactions is determined by density of herbivores. This view is presented by
A.J. Lotka (1925, 1934), V. Volterra (1927, 1927a, 1931, 1931a, 1933, 1937), V. Volterra and U.
Dancona (1935), D. Pimental (1961, 1961a, 1963, 1963a, 1964, 1968), R.M. Anderson and R.M.
May (1980).
Understanding what is the true role of natural enemies in the process might bring clarity in
this controversy. Is it the role secondary, or the primary one?
To begin, consider the interrelations of herbivore populations with their pathogens. In this
context, it should remind the principle or the rule of Farr. This principle is known by the author
from the report by S.P. Ivanov et al. (1938, p. 71). These scholars mentioned it citing R.
Greenwood (1932), and clamed that according to this principle, probability of affection of a
population by a disease depended directly on its density. One more reference of the Farr’s
principle was found in the book by N.P. Naumov (1963, p. 427). Again, it was done as a
substantiation of the increased spread of pathogens with growth of population density. The above
scholars did not report the publication, where this principle was declared.
In fact, at the beginning of outbreaks, disease incidences are very rare. Healthy state of
population of defoliators serves as a reliable indicator that a population is going out of the
innocuous phase.
This fact was used for forecast of probability of outbreaks, in particular of Porthetria dispar.
A method of the forecast was developed by Z. Sh. Yafaeva (1965). According to it, drops of
130
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
hemolymph of Porthetria dispar larvae are examined in a microscope in the conditions of
luminescence. Then, it is possible to see polyhedral particles. An absence of the particles
evidences about high probability of soon arising of an outbreak. Such a method gives a
possibility to find infection in a population of Porthetria dispar long before an appearance of
external signs of the polyhedrosis.
Contrary, at decline of outbreaks, incidences of diseases are numerous, and affection by a
population takes place more and more early in the larval stages.
This claim is illustrated well by the studies of Ja. Komárek (1931, p. 81) with the nun moth,
Porthetria monacha L. In 1921, a laboratory inoculation of larvae of this species with infection
from a nun moth infestation spot resulted in only partial success. A part of the inoculated insects
survived. In 1922, the inoculum from the same infestation spot caused nearly total mortality, but
with a delay – shortly before pupation. In 1923, in a season of decline of this outbreak, the
inoculum caused total mortality shortly after the treatment. Observations in this infestation spot
showed that in 1921, mortality due to polyhedrosis appeared in the larvae only immediately
before beginning of pupation of them. In 1922, the yonger larvae died due to polyhedrosis in the
third instar. In 1923, this disease wiped out nearly all the larvae in the first and the second
instars.
Consider the phenomenon of a change of color of insects defoliators during the process of
population dynamics.
A. I. Il’insky and I.V. Tropin (1965, p. 202) in the chapter on a forecast of density of insect
defoliators reported that before an outbreak side by side with increase of the body weight and
fecundity, it takes place increase of percentage of insects with dark coloration and intensity of
the color. Further, the more expressed the darkening, the more probable a complete defoliation.
These changes were noted in populations of the families Lymantriidae, Lasiocampidae, and
Geometridae (Ibid., pp. 224, 239, 253, 260). In Porthetria monacha, butterflies had especially
expressed black color. These scholars supposed that the changes in color are connected with
onset of drought.
E. Jahn and C. Holzschuh (1970) also noted appearing of dark color (melanism) in butterflies
of Porthetria monacha at the beginning of an outbreak, and explained it as an evidence of
increased resistance to the polyhedrosis. As an outbreak comes nearer to a decline, the butterflies
gain the normal grey color. In so doing, they lost their resistance and are affected heavily with
the polyhedrosis.
In the leaf-rollers (Torticidae), in particular Zeiraphera diniana, the melanism was noted in
larvae at the beginning of outbreaks (Baltensweiler, 1978; Naumenko, 1969).
What is the role of melanization in an organism? The answer was offered by P. Gölz (1973),
namely: producing of melanine in insects is a common response on penetration of xenic
orgnisms in insect’s body, and it is aimed on incapsulation of them.
The change on the population level is a response of a population on a factor of natural
selection. The available data imply that affection by pathogens is a factor of natural selection in
the issue under study. If this is true, the microevolutionary process of the oscillatory pattern takes
place in the course of population dynamics of herbivores.
Above data suggest that in the process, which begins with the burst of vitality of a population
and finishes by "senescence" of it, the important role is played by pathogens, in particular by the
polyhedrosis. In this context, consider the patterns of interrelations of virus pathogens with their
hosts.
The author’s ideas concerning this issue have been inspired by the book of V.A. Zuev (1985).
In this book considering medicine problems, it has been described many findings as to virus
diseases in humans and other vertebrates. Nevertheless, they might be used for understanding the
situation in the insect world. In addition, other publication will be used in the discourse.
A virus infection is able to exist in a host body in four forms. It might be every virus species
can appear itself in all the four forms of infection. They are the following: an acute, a slow, a
latent, and a carcinogenesis.
131
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The form of acute infection
This forms manifests itself at a decline of an outbreak of Porthetria dispar, when trees are
covered with myriad of the died larvae, which have hang being grappled with middle eggs.
The form of slow infection
In vertebrates, this form is a pathological process of long duration comparing to a typical life
span of a species. For example, in a human organism, it continues sometimes during several
decades. It accompanied with a decrease of resistance of an organism to diverse pathogens, so
that it is possible mortality due to not only viral diseases. At the decrease of resistance, in
insect’s bodies, it appears special particles – polyhedres. They are suggested to be a form of
protective response of a host, as a means of inactivation of pathogenic agents – encapsulation of
them.
An amount of the polyhedres can reach up to 30% of insect’s body weight (Ignoffo, 1973).
Naturally, such an intensive protective response needs in expenditures of a significant part of
host organism’s resources. In fact, in 6-7 days after inoculation of larvae of the western oak
looper, Lambrina fisevllaria somniaria Hulst., with the polyhedrosis, i.e. at an appearing of
polyhedres, a reserve of glycogen in their organisms decreases sharply (Morris, 1962).
In this context, it is important observation of P.W. Geier and D.T. Briese (1979, p. 187) as to
the light brown apple moth, Epiphyas postvittana Walker : "Geier and Oswald (1977)
show…that beside killing variable proportion of individuals in laboratory cultures of the
standard CAN strain, common nuclear polyhedral virus (NPV) could cause sublethal
impartments in survivors, resulting in significant reduction of their demographic fitness." In
particular, weight of adults and fecundity (eggs/mg of females) occurred to be decreased in some
cohorts.
Furthermore, the overload of insect’s immune system in a result of the suppression of
pathogenic agents in their slow form increases a possibility of affection of individuals with the
acute form of infection. Such facts were described in literature (see for review L.M. Tarasevich,
1975, pp. 142-145).
Because the acute form of infection kill insects unequally depending on their sex, it is
understood the disturbance of sex ratio at a decline of an outbreak. In diverse species, the acute
form of infection kill mainly females. In particular, this was demonstrated by P.W. Geier and
D.T. Briese (1979, p. 191) for Epiphyas postvittana, namely: "…greater proportion of females
than of males larvae tended to perish in cohorts exposed to the virus." Under impact of the virus,
the proportion of males increased up to 0.87.
The protozoan pathogens exert the effect similar to that in viruses. In fact, I.V. Issi (1968a)
found out that the microsporidian infection transferred from parents to their brood in Porthetria
dispar induced mortality, which was 10-15% greater than that in the check. Also, this infection
led to a decrease of pupal weight and fecundity. The latter was 15% less in the first brood (F1)
and in five times less in the second brood (F2) comparing with parent insects.
The fact of weakening of an insect’s immune system at the slow form of infection allows
bringing contribution in explanation of heavy parasitization of Porthetria dispar populations at a
decline of an outbreak. This effect was demonstrated by N.N. Isakova and T.S. Moyseeva (1968)
in the cabbage pieridid moth, Pieris brassicae L. and its parasite Anilastes ebenicus Grav. as
well as the noctuid cabbage moth, Barathra brassicae L. and its parasite Sagaritis holmgreni
Tschek.
In this study, the larvae of both species were treated with sublethal doses of a preparation
with the pathogenic microorganism, Bacillus cereus , var. galleriae. After that, the treated and
intact larvae were exposed to the parasites. Nearly all the insects treated with the pathogen
occurred to be susceptible to the parasites. Contrary, in the check, 52% of the Pieris brassicae
and 91% of Barathra brassicae larvae were immune to the parasites.
132
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The form of latent infection
At this form, a pathogenic agent is present in its host being in a deeply hidden state. It might
be integrated in the hereditary apparatus of its host. At such a form, the only signs of the
infection are a decrease of body weight and fecundity comparing with the recorded maximum of
these traits. A vitality of such insects is rather high.
Here is a fact that might serve as an illustration of the latent form of infection. S. RoegnerAust (1950) found out in a group of silkworm larvae neatly 80% of individuals having in their
cell nucleus inclusions with polyhedres, whose size was less than typical one. Any signs of virus
disease were absent in the following five generations of the insects. After that, however, an
epizootic burst out. The infection with such weak expressed signs was referred by S. RoegnerAust as a latent state of a disease. The emancipation of the silkworm population from the latent
form of infection lead to a significant increase of its vitality.
Carcinogenesis
At this form, a virus activates a protooncogene, which is inherent in the hereditary apparatus
of a host. The convincing data on this phenomenon are available only for mammals. Some
resemblance of such an effect might be observed in the sawflies (the order Tenthreonidae). It
was reported to be in abdomens of sawflies’ females the inclusions, which were referred to be as
tumors or pseudotumors. They arose in a result of reproduction of cells in larvae under effect of
viral infection and traced in the adults (Bird, 1949; Nuorteva, 1964; Smirnoff, 1968). At
presence of such inclusions, fecundity of the insects was reduced. The percentage of affected
insects occurred to be greatest at a decline of an outbreak, when density of insects was High, and
virus diseases were wide spread within the populations.
The categories of slow, latent infections, and carcinogenesis are embraced by the term "the
inapparent forms of infection."
The factors that determine activity of pathogens in every form of infection
In this context, it is relevant to remember the ideas of I.D. Belanovsky (1931), which are
seemed to be a good base for to come on light this issue. He supposed that presence of "latent
infection" is inherent for populations of insect herbivores. Sometimes, this infection transfers in
the form of acute infection, spreads on nearly all the insects with a population and kill them
during the short period – several days in Porthetria dispar.
The problem is to understand how this transformation proceeds. This scholar paid attention
on the fact that numerous attempts to induce an epidemic in a herbivore population in nature had
a limited success. They included a dispersion of extracts of diseased insects, or dusts of their
dried bodies, or a carry of forest litter from advanced infestation spots in newly formed ones.
Most of these measures failed.
The cause of the fail was understood, when the studies of a number of scholars (Chorine,
Pailott, Hubault) showed that an inoculation per os was much less effective than that by
injection. This was true for Pyrausta nubilalis Hbn. (twelf species of fungal pathogens), the
silkworm (the polyhedrosis), and Dasychira pudibunda L. (fungal and bacterial pathogens). Only
Coccobacillus acridiorum d’Her. infested its hosts equally by per os or proximately in
hemolymph.
For heavy and immediate affection of a population with a pathogen, it needs special
conditions. In search for these conditions, I.D. Belanovsky (Ibid.) did not agree with the
scholars, who supposed that the cause of the mass mortality at overcrowding consisted in spread
of infection by feces of diseased individuals. As an argument, he reminded the lack of such a
mortality at rearing of the silkworm. Its larvae stay in the conditions of much greater density than
defoliators in nature do. Nevertheless, only a less part of aggregations of silkworm larvae dies
133
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
due to diseases, mainly the polyhedrosis – usually up to 10-20%, and seldom up to 40%, whereas
in nature, it is common the larval mortality due to this pathogen close to 100%. A. Paillot
observed that feeding of silkworm larvae by mulberry leaves painted by feces of the diseased
larvae or their hemolymph did not induce affection.
Further, the time passed between two successive outbreaks of defoliators is too long to
infection can be conserved in the soil or on plants. Therefore, it should search for sources of
infection in insects themselves. It occurred to be that these sources are parent insects. Polyhedres
and microsporidia were found out in adults and eggs of many species of insect defoliators. Alike
vertebrates, insects carry infection in their bodies having no apparent signs of diseases. They
transfer it to their progeny, where an epizootic can burst, and they spread on all the population,
when favorable circumstances arise. Now, this phenomenon is called the transovarian way of
infection transferring. Because agents of pathogens can be easily observed in insect’s host
tissues, this is the slow form of infection, rather than latent one.
The next issue of the discourse concerns favorable conditions for arising of an epizootic.
A number of scholars have supposed that disturbance of physiological state of a population at
stress is necessary for the burst of an epizootic. The "stress" means such factors as exhaust of
food resource that forces insects to feed by non host-plants (for review see J. Tanaka, 1976). The
first scholar, who cast a doubt on such a view, seemed to, be again I.D. Belanovsky (1931). He
pointed out that the mass affection of a population often did not demonstrate a dependence on
availability of food and density of this population.
Subsequent studies confirmed this view. "Direct experiments on starvation of caterpillars in
most cases demonstrate the absence of effect of starvation on activation of latent infection in
insects" (Steinhaus and Dineen, 1960, cited in L.M. Tarasevich, 1975, p. 131). According to the
review of literature (Tarasevich, 1975, pp. 108, 131, 135), feeding of insect herbivores by nonpreferable plants in many cases did not activate the inapparent infection.
Moreover, there is the report that at feeding of larvae by leaves with decreased content of
proteins and hydrocarbons, the affection of them with the polyhedrosis is less than at feeding by
food of full value. Such data were offered for the Chinese oak silk worm, Antheraea pernyi
Guer. by O.I. Shetsova (1954).
In some cases, feeding by less preferable plants increased percentage of incidence of the
polyhedrosis. This was shown by H.A. Bess (1961, p. 28) for Porthetria dispar, which fed by
leaves of the aspen, comparing with the best host-plant – the oak. On the other hand, in many
cases, populations of this species were exterminated by the acute form of the polyhedrosis long
before an exhaust of the stock of oak foliages.
For understanding of the mass affection, I.D. Belanovsky (1931) advised to turn the practice
of increase of virulence in pathogens of vertebrate animals. In so doing, an available strain of a
pathogen is inoculated to an animal. After appearing of signs of this disease, blood of the animal
is used for inoculation of next animal of the same species. Such transmission, having a name
"passage", repeats again and again. At every passage, virulence becomes higher. After some
passages, virulence reaches a peak. The same operation was conducted with several species of
insects, in particular the silkworm and Coccobacillus acridiorum, with similar results.
On the ground of above data, I.D. Belanovsky supposed that conversion of the latent
infection in a population of insect defoliators into an epizootic is exerted by stinging parasites –
hymenopterous wasps and those tachinid flies, which are armed by a stinging tool, for example
Compsilura concinnata Meig. and Lydella nigripes Fall. As vectors of infection, it serves also
blood-sucking insect predators, for example the bugs Asopinae spp. In particular, I.D.
Belanovsky cited A.F. Burgess (1926), who recorded affection of a population of Stilpnotia
salicis L. with pathogens in a result of parasitization by Compsilura concinnata Meig.
Why do the passages convert the slow form of infection in the acute one? The slow form of
infection persists until virulence of a pathogen is insufficient to overcome a protective potency of
the immune system of an insect. This is an effect of pathogens of low virulence. In populations
of pathogens, it arises the strains of diverse virulence. If vectors of infection are scarce, the
strains of high virulence tend to disappear shortly, because longevity of affected by them insect
134
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
hosts is much less them those affected by the strains of low virulence. When dying, such a host
gets out from a pool of infection sources. In such a situation, the strains of low virulence thrive
in a host population. Contrary, at the abundant vectors, strains of high virulence spread in a host
population intensively forcing out ones of low virulence. Then, the acute form of infection
affects a population of defoliators.
I.D. Belanovsky offered many data as to high biting activity of the vectors. The instinct of
stinging is very potent. Even infertile females of parasites persistently attack their hosts. Being
attacked by parasites or bugs, healthy larvae of defoliators defense themselves tenaciously.
Therefore, significant parts of the pricks occurred to be futile in term of oviposition. Although
the eggs are not laid, the inoculation can take place. The diseased insect hosts are also attacked
by parasites. It was observed that parasites prick feebly hanging motionless larvae. The dying
caterpillars are sources of most virulent strains of pathogens.
The role of pricks is not limited by inoculation. A prick by itself is an injury, which
predisposes a host to catch a pathogen or to activation of own infection of the slow form. In
addition, hemolymph, which poured out of a host’s body and contacting with air, becomes a
poison. When it penetrates again in a body of a larva at a subsequent stinging, it induces
something similar of the anaphylactic shock. It sometimes results in sudden death.
Further, in the cited article, it has been given for a number species of defoliators the cases of
"epizootics of great potency with a lightning speed", which is caused by high activity of stinging
parasites (Ibid., pp. 276-277). In particular, he described a collapse of mass outbreak of
Porthetria dispar in the Kyiv Region in 1927 with the polyhedrosis as the main cause of it. In
1926 and 1927, oak stems in the infestation spots were covered by huge aggregations of cocoons
of Apanteles fulvipes Hal. In addition, in 1927, it appeared great many predaceous bugs,
probably Picromerus bidens L.
The role of parasites as vectors of infection is not less one than that as direct factors of
mortality of defoliators. It seems, there are the ground to consider the both mortality factors as a
unified entity defining it as a parasite-pathogen complex.
It should note that affection of a population of defoliators by the acute form of infection is
possible at the absence of vectors, although intensity of the affection in this case is lower. An
example of such a situation was provided by G. Wellenstein (1942, p. 240) at studies with the
nun moth, Porthetria monacha in an outbreak in the East Prussia. Mortality of the eggs, larvae,
and pupae on trees in nature equaled the following values: 1934 – 54.3%, 1935 – 89.7%, 1936 –
89.2%, 1937 – 99.9%. In the cages on spruce twigs, i.e. at absence of the parasite effect, the
values of mortality were 40.6%, 61.1%, 83.6%, and 93.7%, respectively. Here, it is remarkable
the steadfast growth of virulence of pathogens, which overcome resistance of host’s immune
system even at absence of stinging parasites.
Humidity of ambient media is an important factor that determines operation of a given form
of infection. In this context, again should turn to I. D. Belanovsky (1936). He has reported that at
heavy rains, a population of Porthetria dispar dies nearly completely due to diseases during
three days. The same phenomenon was noted by R.W. Campbell (1973, cited in R.W. Campbell
et all., 1978, p. 25) in the following words: "… heavy precipitation in June…, if sufficiently
wide spread, may indicate the abrupt collapse of the outbreak phase…"
Consider the causes of such an effect of precipitation. The infection of the polyhedrosis is
contained only in some insects’ tissues of Porthetria monacha. Firstly, it affects epidermis, lately
– muscles and nervous system, but into gut epithelium, it does not penetrate. This fact was
reported by J. Komárek (1931, p. 82). Since the infectious agents are absent in larval feces, the
latter cannot serve as a source of infection. Therefore, a transfer of the pathogen among a
population is possible on condition that body cover of diseased insect becomes broken. Then, an
infection comes out.
As to Porthetria dispar, the same was noted by L.M. Tarasevich (1975, p. 28). The quick
breakage of integrity of an insect’s body occurred, when it is affected with fungal pathogens.
They might be Entomophaga aulico Batko or related species (Weiser, 1972, pp. 320-322). That
is why the polyhedrosis spreads intensively in the conditions favorable for fungal infection. The
135
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
prerequisite of activity of fungal pathogens consists in the high humidity of air. In this context, it
is relevant to cite J.W. Deacon (1983, p. 31), who has reported as to fungal pathogens of insects
the following: "…a high relative humidity (at near 100%) is always needed in the initial stages of
infection…"
The effect of high humidity is especially potent if it is accompanied by significant decreases
of air temperature, i.e. at cool rains. In such conditions, the immune system of insects denies.
S. Metalnikov (1927) showed that at ambient temperature below 10°C, an activity of phagocites
stopped completely.
Naturally, the effect of precipitation depends on the phase of population dynamics, because
affection of a population with the inapparent form of infection is unequal in the diverse phases.
A healthy population at the beginning of an outbreak is a little sensitive to this factor.
Nevertheless, the amount of precipitation in June, i.e. in the period of intensive growth of
Porthetria dispar larvae, determines the trend in population dynamics of this species if the
density has reached the Intermediate level. It can be used for forecast of its density in the next
season, beside with density of eggs-masses in spring of the same season. This dependence was
demonstrated by R.W. Campbell (1967, 1973).
When a load of the inapparent form of infection in a population of defoliators is high, even
weak precipitation can provoke a burst of the acute form of infection. Such a case was shown by
P. M. Raspopov and P.M. Rafes (1978) for Porthetria dispar. This was the situation, when the
population underwent severe suppression by mortality of embryos in preceding years. Probably,
the mortality of embryos was insufficient to clean this population from the polyhedrosis. The rest
of the population having infection in the inapparent form was wiped out in the larval stage by
short rain.
The form of slow infection is characteristic for the groups Protozoa and Bacteria. Ja. Weiser
(1972, p. 474) has reported that protozoan pathogens spread by various ways – with feces of
Porthetria dispar larvae and adults (meconium), at stinging of parasites for oviposition,
including unsuccessful pricks. Weather situation does not exert effect on activity of them. These
features combined with the wide range of hosts that are common for a species of protozoan
pathogens. The transovarian transferring of infection and delayed negative effect on insect hosts
open for the pathogens wide prospects for suppression of diverse species of defoliators.
The affection of a population with protozoan (microsporidian) pathogens and its responses
are demonstrated by studies of L.M. Zelinskaya (1980) in the Lower Dnieper Area in Ukraine.
Here, at the beginning of an outbreak of Porthetria dispar, the protozoan pathogens were
recorded in 12%-19% of the insects, at the eruptive phase in 30%-40% ones, and at the decline –
in 69%-92% of the observed insects. Due to the affection, a decrease the fecundity in diverse
plots varied from twice to nine times. Eggs of the infested females were less resistant to winter
frost. An unhatching of larvae was in 58% of them, whereas in the eggs without the infection, it
was in 34% of cases. Mortality due to this pathogen and others was recorded mainly in the first,
the second and the third instars, and as whole was evaluated as reached 59%. Level of
parasitization in the population was high supposedly due to low mobility of the larvae affected
by the pathogens.
The response of a population of Porthetria dispar on affection by Bacillus thuringiensis was
studied by E. Videnova (1987) at treatment by a preparation of this pathogen in the stage of
young larvae. This treatment induced mortality mainly the future females, so that participation of
males among the hatched butterflies reached 90%.
At a prolonged decline of an outbreak, it is observed a succession of prevailing diseases that
might be explained by natural selection, namely: severe mortality due to a given pathogen
increases resistance of a population to this species, but as to other pathogens, the resistance
occurs low.
Here is the case provided for Porthetria dispar by L.P. Chelysheva (1971). In 1966, when
larval density was 396 insects per tree, 50% of them died due to the protozoan and viral
pathogens; in 1967, with the density 184 larvae per tree, above 99.9% of them died due to the
polyhedrosis; in 1968, with four larvae per tree, above 95% of them died due to a bacterial
136
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
pathogen; in 1969, with two larvae per tree, mortality due to this bacterial pathogen was less
50%.
An increase of affection of a population of defoliators by parasites from beginning to decline
of an outbreak can be only partially explained by weakening of their immune system at
accumulation of the slow form of infection and operation of the effect CESPPs 2.5.2. ''Attraction
of predators and parasites, increases of their searching activity.'' This increase is enhanced by the
microevolutionary process, which leads firstly to loss of insect host resistance to parasites. After
a decline of an outbreak, this leads to selection of resistant insects during the innocuous phase.
The data on this issue are scarce. In this contex, it is relevant to cite the studies of population
dynamics of Zeiraphera diniana (Clark et al., 1967, p. 134). The "progressive phase occurs
because of the vigour and high reproductive ability of the "strong" individuals and freedom from
disease and parasitism."
This statement means that at beginning of an outbreak, the population is resistant to these
groups of natural enemies. The initial state of the population is characterized as "the extreme
"strong" type" (Ibid., p. 136). When density of the budworm becomes High, the larvae are forced
to leave their web shelter in search for food. Then, they are subjected by insistent attacks of
parasites, which, however, are not able to kill them, but infest with pathogens. In so doing, it
arises "the stressed strong type" (Ibid., p. 135). Resistance of the larvae to pathogens is lost more
quickly than that to parasites. After severe selection due to pathogens, in the population, it arises
"the weak type", which is characterized by high resistance to pathogens, but low resistance to
parasites (Ibid., p. 127). Then, parasites decrease the population to very Low density. In so
doing, it takes place selection of the population on resistance to parasites. Further, at very Low
density, the population becomes free from all the forms of pathogens. By such a way, it arises
possibilities to a burst of the next outbreak. It is realized if CESPPs 2.1.2.1.1. "Superevasion
from herbivores" does not operate.
Some reports might be considered as the cases of the same process in other defoliators. For
example, it is concerned to Porthetria monacha (Bakhvalov et al., 1988). These scholars
reported that a decline of an outbreak of the species at High density, affection by the parasites
and pathogens exceeded 90%. Contrary, during several seasons after the decline, when the
density was very Low (0.2 – 0.3 larvae per tree), the mortality was only 18.8%. Hence, in spite
of attacks by abundant parasites, the population kept significant level of resistance to the
complex. This fact might be explained by increased resistance of the population both to parasites
and pathogens.
Consider another line of thinking, which explains variability of vitality of herbivore
populations by effects of inbreeding and outbreeding. To proof of this hypothesis experimentally
is a difficult matter. Nevertheless, its validity might be evaluated by the method of precedents.
This means to trace a behavior of the herbivore populations established by small groups of
animals, which have invaded in isolated from their species areas – continents or islands. The
behavior of such (exotic) species is well known, because they set up serious problems in areas,
where they have penetrated.
The number of individuals in a group of the invaders is very limited. It is known nearly
exactly in vertebrate animals. The population of the European rabbit, Oryctolagus cunicularius
L. in Australia is a progeny of "some dozen" of the animals brought from Europe in 1853
(Fenner, 1965). Two males and six females of the common pheasant, Phasianus colchicus L.
were brought to the Protection Island; in five years, the number of this species on the island
occurred to be equal 1325 birds, i.e. the increase was 166 times (Solbrig and Solbrig, 1979, Ch.
13). The European population of the musk-rat, Ondatra zibetica L., which here and there became
so numerous to get a status of a pest, is a progeny of five animals released near Praha (Elton,
1958). This scholar also reported that releasing of several pairs of the European starling, Sturnus
vulgaris L. in an American park resulted in the burst of density of these birds.
As to insect invaders, it is known the only single report about the number of penetrated
individuals. R. Edwards (pers. comm. in 2002) has supposed that the current invasion of the
western rootworm, Diabrotica virgifera virgifera LeConte in Europe, which threatens growing
137
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
of the corn over the continent, has begun from a single gravid female transported in a plane from
Chicago to Belgrad in 1980-ies.
The number of Porthetria dispar larvae, which escaped from the laboratory of L. Trouvelot,
was probably insignificant comparing with that inhabited an ecosystem of its host-plant in the
Old World.
In all these cases, populations of the newcomer species absolutely underwent inbreeding that
had not precluded reaching by them High density. Firther, with increase of density, hereditary
variability in a population also grows. This fact noted by a number of scholars. According to
I.I. Schmalhausen (1946, pp. 189-190), this regularity has been proved for insects (Ford and
Ford, 1930) as well as for the house mouse, Mus musculus L. (Kalabukhov, 1941). Within
seasonal fluctuations of species density, this regularity also takes place, namely: in summer
generations of the fruit fly, Drosophila melanogaster at very High density, the variability is
much than that that in fall at less density (for review see I.I. Schmalhausen, 1946). W.E. Wallner
(1987, p. 330), when citing R. Carson (1962), has mentioned that "enormous increases in genetic
variability occur as the population reaches its culmination."
In this context, it is of interest the case of propagation of a pair the wallaby in the new
environment. A male and a female of these animals escaped from a zoological garden on an
island of the Hawaii in 1916. After fifty years, i.e. during the period of sixty generations of the
species, the population of them reached 400 animals and was prosperous. Being established by
two animals, this population acquired traits so differing from typical ones for this species that
scholars claimed the phenomenon of an "instantaneous evolutionary change."
The reports concerning diverse organisms do not verify the suggestion as to detrimental
effect of inbreeding. Here are two examples. The crossing of brothers and sisters in the progeny
of a couple of the fruit fly, Drosophila sp. did not lead to any disturbances of vitality in the
laboratory population (Gowen et al., 1946).
"In 1977, a few strands of hydrilla – an aquatic weed – were spotted in California’s All
American Canal. Now, it infests more than 400 miles of important southern California
waterways" (Senft, 1981, p. 4). It seems, even the vegetative reproduction does not preclude
thriving of a species.
Consider one more case of population dynamics of a herbivore species. The question is the
pony in the Sable Island in Atlantic Ocean. This population has arisen from twenty horses
brought to the island several centuries ago. These animals, which have become wild, every
winter suffer due to food deficiency, which has lead to a decrease of their body size. After
particularly severe winters, their density drops nearly twice comparing with that after a common
weather situation in winter. Over several subsequent years, their fecundity occurs low. However,
such stresses have not resulted in any senescence of the population. Contrary, when a group of
large stallions was brought from outside and released on the island with the aim of
"improvement of heredity", native stallions killed them completely. Thus, pygmies happened to
be stronger than giants.
This case is interesting as to speculations about causes of state of a population – its health or
senescence. Obviously, inbreeding over numerous generations does not preclude thriving of a
population. Absence of predators, which play "sanitary" role, is unimportant also. The only
factor limits an amount of a population – availability of food. This factor is of both concerns - an
ecological (it determines density), and evolutionary (it determines evolution in direction of a
decrease of body weight). Shortage of foodstuff kills animals with worse physiological state and
decreases of fecundity, but does not decrease vitality of a population. Although this population is
obviously "stressed" by continious deficiency of food, it is not affected by pathogens. It might be
characteritic for the specific conditions of a small oceanic island, where vectors of pathogens are
absent.
Nevertheless, this is an argument in favor of prevail role of vectors as factors of epidemics,
whereas physiological state of host organisms is of secondary one. The senescence of a herbivore
population is an effect of the parasite-pathogen complex. When an effect of these natural
138
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
enemies is weak, if any, a population keeps its vitality over unlimited time, and amount of this
population will be determined only by availability of food.
Consider population dynamics of exotic species of defoliators that, it seems, corresponds the
above suggestion.
According to E.H. Forbush and Ch.H. Fernald (1896, p. 5), Porthetria dispar larvae were
released outdoor in America in 1868 or 1869. In the first twenty years, this species was unseen.
But in 1889, it appeared in huge numbers near by the house of L. Trouvelot in Medford. After
that, abundance of the species spread on Myrtle Street, forest plots, and a bog. Futher, it took
place the intensive expansion of the species, and it was so abundant that human life was
threatened. Only in 1908, it came some relief.
The period approximately from 1889 to 1907 is characterized by insignificant affection of the
population by parasites and very high fecundity. As an example of parasitization, it can serve an
affection by them in 1895 the 7.5% female pupae and 9.7% male pupae (Forbush and Fernald,
1896, p. 329). The larvae were sometimes "nearly covered" with eggs of the tachinid flies, but
when the 235 larvae bearing from 1 to 33 parasite’s eggs were placed in cages, 226 butterflies
were emerged (Ibid., pp. 385-386). The fecundity reached 1400 eggs that was never observed in
the Old World. An affection of the population by diseases was not recorded.
Nevertheless, the relief set in. What is its cause? In 1905, it was practiced the first release of
Porthetria dispar parasites imported from Europe. In 1907, it was noted the first signs of
affection of the population by pathogens. In 1908, "…myriad of caterpillars in the first stage
were found "wilting" in the forest Melrose, and when just a little later practically every
caterpillar was destroyed in one particularly locality there seemed to be reason to hope for
speedy relief through disease" (Howard and Fiske, 1911, p. 98).
R.W. Glaser (1915) reported that this observation was "the first printed record of wilt in
North America", and that "It may have been introduced with parasites imported in 1905." After
that, abundance of Porthetria dispar and its damage for vegetation became low until the middle
1920-ies. In 1925, a new expansion of this species began.
Why did the affection of American population of Porthetria dispar by pathogens occur to be
so potent? The cause consists in the fact that this population since 1880 existed in the conditions
of absence of pathogens. The genes of resistance to pathogens disappeared in the population, and
it became defenseless to the imported parasite-pathogen complex. Again, it took place a
microevolutionary process.
The similar events are known in the following species: the spruce sawfly, Diprion hercyniae
Hartig. (Baird, 1956; Cameron, 1956); the winter moth, Operophthera brumata L., in
1954-1958, six parasite species were been introduced, and in 1961, a virus disease was recorded
(Embree, 1971); the Japanese beetle, Popillia japonica Newm., forty parasite species were
introduced between 1920 and 1933 from Orient, and "the milky disease" appeared soon (Carson,
1962, pp. 96-97).
In all these instances, the common succession of events might be traced that indicates an
operation of certain regularity. It includes several points as follows:
i) At penetration of a herbivore insect species in an isolated area, the damage due to its
activity takes place with a delay – after the period of roughly ten years. It is called "the
period of waiting."
ii) After that, the period of heavy damage begins that obliges an importation of parasites
from native areas of this invaded species.
iii) In a few years after importation of parasites, it appears diseases, which affect a population
of an exotic species, and its damage becomes less.
These phenomena were described by K. Friederichs (1930, Ch. 26) for a number of species –
the burst of vitality of invaded herbivore species, including high body weight, increased
fecundity, a lack of diseases. He proposed a special term for definition of this phenomenon – the
euphoria.
Among the cases described in the cited book, it is of particular interest is that concerned the
Indian horn beetle, Oryctes rhinocerus. It penetrated into the Samoa Island at the beginning of
139
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
XX century, so that in 1909 – 1912, it took place heavy mortality of palm plantations. In that
time, a body size of the beetles was unusually large. In the males, it reached 51.7 mm, and in the
females, - up to 41.5 mm. In 1913, a body length of the beetles of both sexes occurred to be
shorter – 30 mm and less, while many beetles were affected with the fungus disease,
Metarrhizium anisopliae Metch., and the damage for host-trees decreased. In this case, an
importation of parasites was not conducted. The affection was due to adaptation of a resident
pathogen.
K. Friederichs found hardly to suppose a cause of the great size of beetles’ body in the period
of heavy damage pointing out that food factor cannot be used for this purpose. Indeed, when
manipulating with food, it is possible to decrease a body size comparing with typical one for a
species, but it is impossible to increase the size by this means.
As an explanation of the euphoria, K. Friederichs proposed that it is a result of particularly
favorable climatic conditions in the territory of an invading. It is doubtful, in particular, because
little of probably that climate in North America is more favorable for Porthetria dispar than
diverse climates in Europe and Asia.
Another explanation is the following:
i) At absence of parasites – vectors of pathogens, a herbivore population undergoes a
cleaning from all the forms of infection – acute, slow, and even latent one.
ii) In the conditions of absence of pathogen’s vectors, the cleaning occurs, because strains of
these forms of infection die off together with host individuals affected with them, so that
dissemination of pathogens is stopped.
iii) The cleaning is realized by abiotic factors and unclear biotic ones, which eliminate
preferentially organisms loaded by pathogens in any form of infection, while completely
healthy organisms survive; body weight of them and fecundity become greater than those
in the native range.
iv) With completion of the cleaning, the period of waiting ceases; then, an expansion of an
invaded species begins. This is the period of euphoria.
In the periods of waiting and euphoria, probably mainly predators consume an invader, but
they cannot suppress it, even if they cause high mortality.
In fact, in North America, according to E.H. Forbush and Ch.H. Fernald (1896, pp. 25, 95),
fecundity of Porthetria dispar reached 1400 eggs, while an increase of its density was no more
than seven-fold (6.42), i.e. this mortality per generation was equal 99.2%, if to suggest the sex
ration to be close to 50:50. Thus, in the period of euphoria, the only effective suppressive factor
is a starvation of a population of an exotic species. This implies the exhaust of food resource, i.e.
heavy damage of host-plants.
After importation of parasites into the new range of a herbivore species, it arises possibilities
for expansion of pathogens and affection of the species by them. In a result, it takes place
pronounced decrease of vitality, in particular fecundity of their hosts. In fact, in Porthetria
dispar now "…where conditions are optimum, egg clusters average about 750 eggs, compared
with about 300 eggs at the end of an outbreak…" (Leonard, 1981, p. 12).
In Europe, the fecundity lies in the range 300-700 eggs (Veinstein, 1951). According to V.I.
Benkevich (1984, p. 59), the range of fecundity in this species is 180 – 400 eggs depending on its
density. There is, however, a report about greater fecundity, in particular 1015 eggs (Rudnev,
1951). This value likely to be found by means of calculation after the formula of the dependence
of moth’s fecundity on weight of a female pupa. The result of the calculation might be
inadequate to the reality, particularly at the large values.
Since Porthetria dispar spreads in the recently infested areas sooner than its parasites do, a
population of this species is able to acquire features similar to those in the period of the euphoria.
The evasion from parasites of an exotic herbivore species, in particular Porthetria dispar, is most
probable in the island infestations outwards of quarantine areas, which have been settled to stop
its expansion (the map of these infestations can be see in R.L. Telerico, 1981, p. 33).
140
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Consider the data in favor of this idea. R.W. Campbell (1981, p. 78) has reported that
"Recent results suggest that fecundity may be exceptionally high near the advancing front of the
generally infested area." Such a situation is characteristic for the population free from pathogens.
The R.W. Campbell’s report is in the well concordance with the C.C. Doane’s (1976)
hypothesis that the nuclear polyhedrosis virus exhibits a time lag as to its activity in the recently
invaded areas. This suggestion does not mean, however, that diseased individuals of Porthetria
dispar lack in the advancing front of the generally infested area. In fact, M.R. Carter et al. (1991)
studied the causes of its mortality in seventeen sites of the advancing front and found out that the
most significant causes of the mortality were the polyhedrosis and starvation.
The comparative role of these causes of mortality depends on circumstances, particularly on
possibilities of parasites to accompany their hosts. In this context, the valuable study was
conducted by M. Ticehurst (1981) in the advancing front of the generally infested area. It
occurred to be that at heavy defoliation in 1974 and 1975, the percentage of stinging parasites –
vectors of pathogens (Apanteles melanoscelus and Phobocampe disparis) was negligible –
0.6-0.7% and 0.0-0.1%, respectively. At such low values of vectors, disease incidence would be
small.
Contrary, at a collapse of the infestation in 1978, the number of these parasites reached 9.7%
and 12.4%, respectively. At such values of vectors, significant mortality due to the polyhedrosis
is probable. Unlike to it, well flying tachinid flies reached appreciable values just at the
beginning of the outbreak phase – in 1974, namely: Blepharina pratensis – 21.4%, Brachymeria
intermedia – 9.8%. However, because they are not the vectors, these species did not preclude the
growth of Porthetria dispar density.
In vertebrate herbivores, an operation of the effect 2.5.3. "Increase activity of pathogens and
parasites in the specific conditions of high host density’’ has been shown by numerous studies.
In particular, mass epizootic of the plague took place only in the locations, where density of the
ground squirrels, Citellus spp. was not less than 11-16 animals per hectare (Ivanov et al., 1938,
p. 72).
Again, diverse forms of infection might be traced in them as responses on population density.
C.H. Andrewes (1967) reported that an increase of pathogen virulence in the conditions of an
easily spread of infection is a common feature of animal populations. At epidemics in human
society, values of mortality are in direct dependence on the number of disease incidences. In the
period of a peak of epidemics, mortality is always higher than that at a beginning or at a decline
of epidemics. This is a case of the acute form of infection thriving in the conditions favorable for
a spread of a pathogen.
E. Traub (1939) studied over a number of years an affection by the lymphocytic
choriomeningitis of a population of the house mouse, Mus domestica L. He noted that it began as
a contagious disease with high percentage of mortality, but after several years, it became a
hereditary disease with nearly absent signs. The mortality due to this pathogen was stopped.
However, the fecundity and indices of vitality in animals with the inapparent form of infection
were less comparing with those in the healthy ones. E. Traub called such interrelations between a
virus and its host "a perfect form of parasitism." This is a case of the slow form of infection. At
certain conditions, it can convert in the acute form of infection.
In a population of the vole, Microtus agrestis, D. Chitty (1957) found out an increase of a
spleen. This phenomenon is observed over several years after finish of the period of High
density. J. Dawson (1956) has showed that this is a pathology – the non-contagious hemolytic
anaemia. Thus, this is a similarity of the carcinogenesis as the inapparent form of infection. To
consider this phenomenon as pathology is a novelty, because there exist the view that that is
a genetic change of an adaptive character.
The view of J. Dawson was confirmed by the studies of E.I. Boikova (1972). The object of
the study was an immigrated population of the Siberian lemming, Lemmus sibiricus, which
suddenly appeared outside of its natural range in the middle of June 1970. This study was
conducted in a flood plane of the River Sob, the Polar Ural Mountains. The dissection of the
trapped animals, that began at once after their appearance, showed that they were supplied
141
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
sufficiently by food, but weight of their spleens increased very sharply over a month. In July, the
weight of spleens was three times much in the females and twice as much in the males
comparing with that in June. This is a sign of a disease. Already in August, this population died
off. The resident species, the hoofed lemming, Dicrostonyx torquatus. was on the Low level of
density that suggests abundance of forage for the immigrants and a lack of sources of infection
for the immigrants. Therefore, the immigrated population died off due to own infection.
This study is valuable as to two lines. Firstly, it showed that increase of weight of an inner
organ in result of overcrowding is a pathology, rather than an adaptation. Secondly, the cause of
this pathology is an effect of High density, rather than a food deficiency.
The next task is to trace connections among density, affection of pathogens and predation in
populations of vertebrate herbivores. In this context, it is important the review on the population
dynamics of a number species of game animals and pest rodents offered by S.A. Severtsev
(1941). In particular, as to the snowshoe hare, Lepus americanus faenotus, it was considered in
detail the data of E.T. Seton (1910, 1920) and Ch. Elton (1931-1935).
The pattern of fluctuations of its density is very regular with duration of the cycle close to ten
years. A growth continues over five years, and a decline – over two years (Severtsev, 1941,
p. 161). The main cause of a decline of a hare populations is affection by pathogens – especially
Staphylococcus piogenes, Strongilis strigosus, and others. In addition, it is important the
helminthes invasions - Fasciola hepatica, Sintetocaulus sp., and Cisticercus pisiforme.
The epizootics decrease the density during the short period. Usually they began in fall and
winter and finished after several months. In the next year, density decreased due to unknown
causes, so that during two years, the density changed from approximately the 1000 animals per
square mile to a single hare per the same area. The epizootic burst in areas with the maximal
density and spread on near by ones with less density of the haires (Ibid., pp. 158-159).
A density of the lynx, Lynx lynx L., the hare’s main predator, grew with increase of hare’s
density, and droped sharply with a decline of a hare’s outbreak. In that time, the weight of lynx
body decreased from 25-28 pounds to 12 pounds, and a hunter in the region of the river Atabaska
found out during a month up to 30 corpses of the lynx died due to starvation (Ibid., p. 168).
The similar pattern of population dynamics is characteristic for the European hare, Lepus
europeus L.. These data were offered by N.V. Turkin (1900), who operated by the reports about
an export of hare’s skins from Russia to Western Europe from 1824 to 1897. In North America
and Russia, outbreaks of hares took place in diverse time that contradicted the hypothesis as to
effect the solar activity on population dynamics of the animals. In Russia, the cycle was close to
5-6 years. Weather conditions exerted significant effect, which disturbed the regularity of
outbreaks. Weather situation in winter determined availability of food, whereas wet weather in
summer increased affection by helminthes (Ibid., pp. 161, 164).
The detailed information about processes at decline of hare outbreaks was offered by
S.P. Ivanov et al. (1938, p. 72). They reported: "Elton, Ford and Baker (1931), Berdnikov
(1934), Pokrovs’ka (1935), A.N. Formozov (1935) showed that the main causes of the decline of
hare outbreaks were epizootics, which embraced areas of hundred thousands square kilometers
and killed hundred thousands or millions hares, whose corps were numerous. The mortality was
caused by bacteria, protozoans and helminthes. It was common the rabbit-fever, the
pyroplasmosis, vectoring by mites, the septosemia induced by Bacillus diploralis, and the
pseudotuberculosis. At affection by the "blister disease" induced by the cystocerk Taenia
serrata, hares became weak and lean, but they died only in unfavorable conditions. Weakened by
the blister disease hares were an easy prey of predators (dogs, wolves and foxes). In guts of these
predators, the cystocerk matured, left its hosts with excrements and occurred on grass, which was
fed by hares, so that the predators promoted the affection of the preys. The liver parasite
Fasciola hepatica needed in additional hosts – mollusks, which inhabited wet habitats…Studied
in Canada by Boughton (1932) showed that hares were more affected in wet habitats and in
seasons with abundant rains."
This report is notable as to demonstration that vertebrate predators serve as vectors of
herbivore pathogens and parasites.
142
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The affection of hares by diseases was so common that Russians avoided feeding by these
games, and used of hares only as a source of skin (Severtsev, 1941, p. 168). It is known
a number of hare diseases contagious for people. Tularemia, Francisella tularensis, the family
Brucellaceae is most common. This pathogen demonstrates the absolute record of virulence for
people. Even ten these microbes induce the disease, and susceptibility of people in all the ages is
close to 100%. The American race, F. tularensis nearctica is the especially virulent, and most
cases of the disease were recorded in the USA (Vinogradov-Volginsky et al., 1973, p. 377-381).
Other hare diseases contagious for people are the following: mite encephalitis, mite rickettsiosis,
haemorragic fever, salmonellesis, brucellesis, leptospirosis, dicroceliosis, and plague.
S.A. Severtsev (1941, pp. 206-208) offered a review of literature, which dealt with some
subtle features of development of epizootics in vertebrate herbivores. These studies conducted by
W. Topley (1926) and M. Greenwood (1932, 1932a) were reported in a medicine journal, and, as
S.A. Severtsev wrote, were not noticed by ecologists. It is relevant to remind them now.
In the studies, it was observed a state of mice, which had been placed in cages in the
conditions of inoculation by the mouse typhus, Bacillus aetrike, at diverse variations of mice
density. It was found out two phases in development of the epizootics similar to those in
epidemics of people. The initial, “fore-epidemic phase” was characterized by incidence of
mortality, but it was impossible to find agents of the pathogen in died animals. After some delay,
it took place a burst of disease with apparent sings of the inoculated pathogen. This was the
epidemic phase. Then, it increased the number of animals, which spread infection, but they did
not fall in the disease. Some diseased animal survived, but they served vectors of the infection.
Indeed, if to set healthy mice to survived or non-diseased ones, mortality appeared again in the
entire stock.
If during the fore-epidemic phase, when mortality began, to decrease density of the mice by
culling moribund animals, the inoculation faled. The culling eliminates the most virulent strains
of pathogens.
This result has allowed drawing the important conclusion as to the method to stop epidemics:
it needs sanitary measures at the very beginning of it. The predators having the developed
selectivity at hunting of their preys play the role of sanitary factor in nature. The predacious birds
are extremely selective as to the state of healthy of rodents.
In fact, N.P. Naumov (1963, pp. 484-485) and A.M.Chel’tsov-Bebutov (1982, pp. 78-79)
offered the review of literature showing that students of a plague infection used collection and
analyses of remnants of rodents under eagle’s nests. The steppe eagles serve as "plague
indicators" for epidemiologists. In samples of the preys, the plague infection becomes seen much
earlier than that at mass trapping of rodents by epidemiologists. The same is true for the
leptospirosis, helminthes invasion, and diverse pathologies in preys of a number species of the
predacious birds.
In the past, when predacious birds were not been yet suppressed by people, epizootics of the
plague might be stopped at beginning. The predators were not able to prevent growth of prey
density, but sanitation of a prey population, when its density only began to grow, would prevent
appearing of the acute form of infection. A decline of outbreak would proceed with operation of
the slow form of infection. Then, the danger of a spread of the infection on people would less.
It is relevant to cite A.M. Chel’tsov-Bebutov (1982, p. 79), who reported that at growth of
rodent density, the main part of bird’s preys consists of healthy animals including females. The
obvious cause of the greater susceptibility of rodents to predators at beginning of growth of their
density is the need to move on larger distance in search for food, and emigration of young
animals. Nevertheless, these healthy in appearance animals can be vectors of infection at the
fore-epidemic phase.
As to mammal predators of hoofed herbivores, mainly the saiga, Saiga tatarica, it was stated:
“The role the wolf, Canis lupus L. and other predators in the desert and semi-desert biocenoses
in Kazakhstan was studied thoroughly by A.A. Slutsky. These studies allowed him to draw the
next conclusions: the predators were not the factors, which determined changes of prey’s density.
They were commonly the secondary cause of mortality of them, they killed mainly diseased and
143
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
weak animals that sanitized populations and promoted their productivity” (Fedoseenko, 1986, p.
88).
This scholar showed how populations of the saiga protected themselves against wolves (Ibid.,
pp. 88-89). In the period of calving, saigas aggregated in large groups up to twenty-five thousand
of the animals. In such aggregations, wolves were absent. Outside of such large aggregations, it
was formed less aggregations, where proportion of wolves to sagas was 1 to 150. The difference
in grouping of the saigas was caused by diversity in physiological state of the animals. The
healthy animals produced large aggregations, whereas weakened were forced out of them. In the
period of winter migrations, the saiga also produced aggregations with the different numbers of
the animals and different rate of preying within them. Wolves did not affect the herds going
ahead. In the lag behind herds, mortality due to predation was only 1% if an aggregation reached
several thousands of the animals, and 5% of predation took placed if the number was less 200
animals.
These observations were done in reserves, where it is maintained naturally the proportion of
wolves to saigas 1 to 1000 in winter and 1 to 1200 in summer. In such situation, values of the
predation are evaluated as much less comparing with mortality due to dearth of fodder at
abundant snow cover of “djut” (covering of the soil surface by ice). The wolves consume annual
fall of a prey’s population of the saiga. The main food of the wolf in spring and summer was the
rodents and hares.
The destructive human activity as to mammal herbivores and their predators might be of two
kinds: the first, heavy decrease of density of hoofed animals at retaining of significant density of
their predators; the second, wiping out of the predators. In the first kind, the herbivores become
defenceless to the predators and undergo extinction. The second kind, it arises the situation, wellknown in badly managed natural reserves and game husbandry, where the predators are wiped
out. This leads to heavy damage of vegetation, mass affection of vertebrate animals with
pathogens and parasites. In a result, it takes place a decrease of density of the animals to values
less than that at presence of their predators without human interference.
Thus, it is the grounds to suppose that epizootics in populations of mammal herbivores take
place in ecosystems, which stay continually on the level ESPPs 3.3. "Late control" as the Tundra
biome in respect of the lemmings, or in the ecosystems, whose ESPPs was disturbed by human
activity in term of destruction of predators of the hoofed herbivores. As to the latter, in the
undisturbed ecosystems, the pathogens are kept as the latent or slow infections due to culling
weakened aminals by predators.
It is relevant to put the question: what is the main cause of affection of a overcrowded
herbivore population by pathogens – weakening of physiological state due to CESPPs 2.5.1.
"Deterioration and/or shortage of food" or increased activity of pathogens and parasites with
growth of herbivore density, i.e. CESPPs 2.5.3. "Increase of activity of pathogens and parasites
in the specific conditions of high insect host density?"
Some data give evidence in favor of CESPPs 2.5.1. "Deterioration and/or shortage of food."
Indeed, "Matured fatty ground squirrels (Citellus sp.) tolerate the plague more easily than young
ones do, which suffer very heavily at affection by this pathogen" (Severtsev, 1941, p. 209).
However, "In USSR, it is well-known epizootics of the anthrax and the hoof disease in the
reindeer… The epidemics are most developed in warm seasons, when in the tundra the yield of
berries is good. The cause of this dependence is not complicated. In warm seasons, there are a lot
of blood-sucking insects – vectors of an infection. In cold summer, the insects are innumerous
that decreases spread of the infection" (Severtsev, 1941, p. 206). Hence, the epizootics in
a reindeer population burst in seasons with high activity of vectors of infection, despite their
food resource is abundant.
S.A. Severtsev (1941, pp. 195 - 210) argued usefulness of the "principle of collision"
proposed by V. Volterra - Principe de rencontre (1933, 1937) for understading of population
dynamics of animals. In the context of pathogens, this principle might be understood as follows:
the more contacts among herbivores within of its population, the greater probability of affection
144
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
of it with pathogens. A probability of the contacts is determined by a "dynamic density of
population" and an "epizootic density."
The dynamic density of population is a term proposed by Yu.M. Rall (1936). This scholar
developed this concept for the sandy mice. The dynamic density of population is determined by
activity of animals, i.e. frequency, velosity, and duration of their moving that depend on
character of an ecosystem. He conducted studies in the sandy semi-desert with scarce vegetation,
where density of the mice was Low (unnumerous burrows). However, by counting of mice traces
on sand and by catches of them in traps, it was seen that mice moved far from their burrows.
Thus, in spite of Low density, contacts among the animals were frequent. When dynamic density
of population is High, an infection spreads very quickly.
The role of epizootic density is shown by the following example: "In mice rodents (the
family Muridae), in some cases, an epizootic begins at 3,000 – 4,000 – 10,000 burrows per
hectare, whereas at other cases – at 35,000 or even 70,000 –75,000 burrows per this area. It
seems, these differences of epizootic density can be explained easily from the view of
V. Volterra’s Principe de rencontre. The mice live in colonies separated by some space. When
food in abundance, the rodents do not contact with inhabitants of adjacent colonies that makes
difficult to spread of infection. Contrary, at shortage of food, mice are forced to move on longer
distance and to contact with neighbors spreading infection. The latter situation takes place at
drought, when vegetation becomes scarce" (Severtsev, 1941, p. 204).
At last, it should pay attention on important role of activity of vectors of infection that
depends on character of ecosystems, terrain and weather situation. As to the character of
ecosystem, it is approprite to compare the Tundra and Steppe biomes. In Tundra, mosquitoes vectors of infection are abundant in most of season and are aggressive over the prolonged period.
In Steppes, in spite of their xeric nature, blood-sucking flies and mosquitoes in some seasons
also occur, but over the short period. Here, as the vectors, it serves mainly fleas and mites, whose
possibilities to spread infection are not too advanced. Therefore, fructuations of lemming’s
density in Tundra, which are determined by activity of pathogens, are very reguliar, whereas in
Steppe fluctuations of density of resident mice are of low reguliarity. Thus, the very advanced
activity of vectors of infection in the Tundra is the true cause of the uncanny regularity of
outbreaks of the lemmings that so surprises of scholars.
The effect of terrain and weather situation was shown by A.S. Severtsev (1941, p. 205) in the
following examples. In terrains with abundant bogy habitats, density of the hare kept continually
on the rather Low level. The cause consisted in affection of hares with the helminth invasion
fasciolesis affecting liver. This parasite needs in additional host – the mollusk Limnea
truncatula, which is abundant in bogs. Not too large increase of hare’s density resulted in heavy
affection of its population with the parasite.
In the Elba River Valley (Germany), a number or rainy seasons led to affection of the deers
by the fasciolesis and the lung helminthes stringillids. High humidity of the soil surface
promoted survivorship of stringillid larvae, and continual pools were favorable for the mollusk,
so that both parasites thrived.
Thus, the situation with affection by pathogens in populations of vertebrate herbivores is the
same as that in populations of insect defoliators. The main cause of the affection is wide
possibilities of its spread, rather than a stress due to food shortage. Although food shortage
increases dynamic density of a population.
Concluding, the principle of collision is a retelling in other words the principle of Farr, which
has been noted at the beginning of this section. Thus, the vast literature on the problem under
consideration reports about a common regularity.
145
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.5.3. Increase of activity of pathogens and parasites in the specific conditions of high insect
host density
2.5.3.1. Ever-increasing accumulation in populations of the inapparent form of infection
resulting in decrease of body weight
2.5.3.1.1. Decrease of fecundity
This issue has been well studied for Porthetria dispar. Fecundity of this species undergoes
large changes in the duration of an outbreak. Here is an example as to the average number of
eggs per the female proposed by K. Vasiĉ and L. Jankoviĉ (1958), namely: beginning of an
outbreak (progradation) – 700, the prodromal phase – 600, the eruptive phase – 500, the crisis
phase (decline) – 150 – 300. One more example has been offered by V.A. Kolybin and L.M.
Zelinskaya (1975): progradation – 652, the prodromal phase – 452, the eruptive phase – 377, the
crisis – 176 eggs.
The fecundity depends closely on weight of the female pupae (Rudnev, 1936, 1951). Hence,
weight of the females fluctuates also in dependence on the phase of population dynamics. The
same regularity, although less expressed, is characteristic for male pupae of Porthetria dispar.
The study by A.I. Latanov et al. (1971) showed the dependence of decrease of fecundity on
affection of a Porthetria dispar population by pathogens. At decline of an outbreak, in fall, after
heavy mortality due to the polyhedrosis and parasites, density of the egg-masses was 0.3 per tree
with 87 eggs in every mass. In the next season, the density decreased to 0,0004 egg-masses per
tree, but the average number of eggs in it increased to 374. In this season, mortality due to the
polyhedrosis was far less, but the larvae and pupae were attacked persistently by parasites.
The same regularity might be found out, if to study diverse herbivore species over an
outbreak. In particular, A. I. Il’insky and I.V. Tropin (1965, p. 230) reported about fluctuations
in pupal weight and fecundity in the Siberian pine moth, Dendrolimus sibiricus. From the I to IV
phases of population dynamics, which correspond above-mentioned phases in Porthetria dispar,
average weight the pupae decreased from in the larch ecotype 4.0 – 5.0 gr to 1.4 –1.8 gr., in the
Siberian pine and the fir ecotypes - from 2.8 – 3.3 gr to 1.5 – 1.8 gr. The average fecundity in
the larch ecotype decreased from 650-750 eggs to 70-120 eggs, and in the Siberian pine and the
fir ecotypes the fecundity decreased from 400 – 460 eggs to 80 – 100 eggs.
The report by P.W. Geier and D.T. Briese (1979, p. 187) about the light brown apple moth,
Epiphyas postvittana Walker has showed that a decrease of body weight and fecundity can be
induced by treatment with a viral preparation. The same effect is possible at accumulation of
viral infection of the slow form in natural conditions.
A population of Porthetria dispar is free from affection of the slow form of infection only
over the short period – actually only before an outbreak (in the innocuous phase), whereas the
beginning of it is accompanied with the first signs of the pathogen’s activity. This is revealed by
a decrease of weight of female pupae and fecundity in the period, when defoliation has reached
only 5% (Campbell, 1963, 1968). To explain this decrease by deterioration of food quality is
difficult. The response on accumulation of pathogens in the slow form is more probable.
Taking into account this report, one might thought that the above cited study by A.I. Ill’insky
about dependence of pupal weight in Panolis flammea on percentage of consumed needles is
connected not only with decrease of food quality, but also with the slow form of infection.
The effect of forced feeding by non-preferable plants in the conditions of deficiency of
preferable ones on accumulation of the inapparent form of infection is a debatable issue. Some
reports show that this effect does not take place. In fact, at feeding of larvae of Hyphantria cunea
by diverse plants, including the least preferable ones, the accumulation was the same
(Tarasevich, 1975, p. 108).
B.A. Areshnikov et al. (1975) showed that value of body weight of the sunn bug, Eurygaster
integriceps Put. in fall is so valid index of vitality that it can serve for forecast of danger for hostplants in next year. If average weight of the 50 females in a sample taken in sites of hibernation
146
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
in the period from August to the end of October exceeds 130 mg, the density will be above
threshold of damage in next year. If the average weight is less than 115 mg, the danger of
damage is absent. At the lowest weight, mortality of the bugs at hibernation reaches 70-80%.
The survived low-weight bugs have insignificant fecundity and weak resistance to insecticides.
M.P. Dyadechko (pers. comm.) revealed one more defect of a low-weight sunn bug
population: its embryos became susceptible to the telenomid parasites. Contrary, in the eggs laid
by the females of heavy weight, embryos of the parasites were killed by protective responce of
the hosts.
The decrease of body weight in many species of herbivores, particularly in defoliators, can be
induced by operation of the effect 2.5.1.3.2.2. "Decrease of body weight and fecundity" at
CESPPs 2.5.1. "Deterioration and/or shortage of food", but food resource of the sunn bug is
more stable than that in defoliators. Therefore, it is the grounds to suppose that in this case, it
operates indeed CESPPs 2.5.3. "Increase of activity of pathogens and parasites in the specific
conditions of high insect host density." It suggests an accumulation of the slow form of infection
in a population at progressing of an outbreak.
2.5.3. Increase of activity of pathogens and parasites in the specific conditions of high insect
host density
2.5.3.1. Ever-increasing accumulation in populations of the inapparent form of infection
resulting in decrease of body weight
2.5.3.1.2. Decrease of participation of females in sex ratio
In Porthetria dispar, at beginning of growth of density, the sex ratio is close to equal one, but
at the decline, the males prevail. At a decline of a Porthetria dispar outbreak, the proportion of
the females was only 17% (Bess, 1961, p. 25). S.A. Mokrzhetsky (1914, p. 14) reported that at a
decline of the observed by him outbreak, the proportion of the females was 12%, and only 60
eggs were in an egg-tube, while in the beginning of the outbreak, their number in an egg-tube
reached 1200. Also, at the decline, the females were too weak to stretch their wings after
emergence, so that they died having no possibility to lay their eggs.
In Dendrolimus sibiricus, at beginning of an outbreak, the sex ratio is 2:1(females : males),
whereas at a decline – it is 1:2 (Il’insky and Tropin, 1965, p. 230).
P.W. Geier and D.T. Briese (1979, p. 191) showed for Epiphyas postvittana, that exposition
to a virus preparation induced mortality mainly females. This implies that high activity of
infection, rather than the hereditary breakage of a population is a true cause of disturbance of the
sex ratio.
2.5.3. Increase of activity of pathogens and parasites in the specific conditions of high insect
host density
2.5.3.1. Ever-increasing accumulation of the inapparent form of infection resulting in
decrease of body weight
2.5.3.1.3. Mortality due to weather stress and parasites
The directly density-dependent pattern of parasitization is a universaly trend in population
dynamics of herbivores. The increase of its percentage either smooth or spasmodic with growth
of herbivore density from a beginning to a decline of an outbreak is obvious.
The increased mortality of insect herbivore populations by weather factors if they affected by
the inapparent form of infection was considered above at describing of effects CESPPs 2.3.
“Routine weather suppression.”
147
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.5.3. Increase of activity of pathogens and parasites in the specific conditions of high insect
host density
2.5.3.1. Ever-increasing accumulation in populations of the inapparent form of infection
resulting in decrease of body weight
2.5.3.1.4. Mass mortality due to affection by the acute form of infection and parasitization
This effect on a population is the common at ESPPs of the level 3.3."Late control" in openly
feeding defoliators and sap-sucking arthropods. This effect takes place obligatory in the
conditions favorable for thriving of parasites and intensive spread of infection within a herbivore
population. Beside the High density of the openly feeding defoliators, the prerequisites of the
effect are the following:
i) In exotic species, high activity of vectors of infection, which is provided by importation
of their parasites from the native range into the new range.
ii) In resident species, and in naturalized exotic species (those having vectors of infection),
high activity of vectors of infection at onset of weather situation, which favors thriving of
the vectors.
iii) In resident species and in naturalized exotic species (those having vectors of infection),
onset of weather situation, which promotes united affection of the larvae by fungal and
viral infections, as well as suppresses the immune system of defoliators.
The prerequisite “i”
At prerequisite “i”, it proceeds decline of outbreaks of exotic species in few years after
importation of parasites from their native lands. The examples are well-known cases of
suppression in North America Porthetria dispar (Howard and Fiske, 1911, p. 98), Diprion
hercyniae Hartig. (Baird, 1956; Cameron, 1956), Operophthera brumata L., (Embree, 1971),
Popillia japonica Newm., (Carson, 1962, pp. 96-97).
The success of the suppression is determined by High density of the exotic species, so that
the primary role of the effect of 2.5.3.1.4. "Mass mortality due to affection by the acute form of
infection and parasitization" is indubitable. Also, a contribution into the suppression is brought
out by decrease of resistance of populations of exotic defoliators to these natural enemies. The
decrease is probable, because they have inhabited an invaded area over decades at absence of
selection on the part of natural enemies. The above factors result in high efficacy of the parasitepathogen complex.
The prerequisite “ii”
At the prerequisite “ii”, it takes place the burst of efficacy of the parasite-pathogen complex,
when density of defoliators reaches the level "High", and at onset of weather situation favorable
for activity of parasites. The parasites survive well both in winter and summer, they are provided
by imaginal food - nectar because flowering becomes sufficient.
The effect 2.5.3.1.4. "Mass mortality due to affection by the acute form of infection and
parasitization" in the conditions “ii” is characteristic for Porthetria dispar, the spring-summer
guild of defoliators of deciduous trees as a whole, and for Porthetria monacha in the W.C.
Cook’s zone (b).
Within the zone (b), a probability of appearing of the prerequisite “ii” is determined by
climate. In western and northern areas of the zone with rather mild (European) climate, the
weather situation is common. Here, the duration of the outbreak phase (the period of High
density) does not exceed two or three seasons that will be finished by mass mortality due to
affection by the acute form of infection and parasitization.
In the zone (b), it is possible suppression of populations of openly feeding defoliators by
parasites and pathogens at Intermediate or Low densities. That is, however, the level ESPPs 3.2.
148
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
"Lag control" - the restoration of activity of CESPPs 2.2.1. "Natural enemies of invertebrate
herbivores", rather than the effect 2.5.3.1.4.
In southeast areas of the zone (b) with the climate close to continental (Asiatic) one (in
Bashkiria), if drought occurs at the outbreak phase, the phase continues longer than three
seasons. Here, decline of outbreaks, it becomes probable an operation of the effect 2.5.3.1.5.
"Spontaneous or winter mortality of embryos."
The prerequisite “iii”
The prerequisite “iii” occurs often in the W.C. Cook’s zone (b). Here, it takes place the
cooperation of CESPPs 2.3.4. "Cool and prolonged rains in the larval stage of defoliators" with
the effect 2.3.4.1. "Mortality of larvae at inducing of the acute form of infection" and the effect
2.5.3.1.4. "Mass mortality due to affection by the acute form of infection and parasitization."
Onset of the cool and prolonged rains suppresses immune system of defoliators, induces
affection of the populations with fungal diseases, arising of numberless sources of infection due
to breakage of skins of the caterpillars. In a result, a population dies off during a few days.
In the W.C. Cook’s zone (с), the prerequisite “iii” takes place at appearing of High density of
Porthetria dispar due to mass immigration of the species. Contrary, resident population of in this
zone stays on the level Insignificant density nearly continually. Therefore, the prerequisite “iii”
does not occur. In rare cases, the population grows to the level of Low density. The resident
population is kept on Insignificant density or it is returned on this level from the Low level by
common onset of the weather situation, when it operates CESPPs 2.3.4. "Cool and prolonged
rains in the larval stage of defoliators" with the effect 2.3.4.1. "Mortality of larvae at inducing of
the acute form of infection." This effect cooperates with CESPPs 2.2.1."Natural enemies of
invertebrate herbivores", 2.2.1.3."Pathogens." The effect 2.5.3.1.4. does not operate here.
In the W.C. Cook’s zone (d), where density of Porthetria dispar is continually Zero or
Insignificant, the effect 2.5.3.1.4. is absent at all. Here, it operates CESPPs 2.2.1."Natural
enemies of invertebrate herbivores."
The effect 2.5.3.1.4."Mass mortality due to affection by the acute form of infection and
parasitization" operates in the interrelations of vertebrate herbivores with their pathogens and
parasites. The case stories were given above in this Section.
Naturally to put the question: how do social insects (ants, termites, and bees) avoid affection
by all the forms of infection in spite of they continually keep in the conditions of crowding? The
answer is the following: these insects possess advancing traits of hygiene. They produce
substances suppressing an infection, use with this aim protective substances of plants, and
behave correspondingly.
Consider some examples. Samples of volatile and non-volatile substances from termite nests
suppress cultures of soil microorganisms, including Aspergillus flavis, Beauveria bassiana and
Penicillium spp. (Lyutikova, 1987).
The bees sterilize their hives using oleoresin taken from poplar buds. This product (propolis)
is known as an antiseptic, and it is used by people for this aim.
Also, formic acid produced by ants, is potent antiseptic and acaricide recommended for
protection of bees from mites. Moribund ants are taken away anthills. Weak ants leave their hills,
and rise on grass tops, where they die. In such conditions, their bodies dry up quickly, so that
they do not serve as sources of infection.
A similar trait has been found out in the bees, which are affected by an unidentified virus
desease in America and Europe in 2007. The deseased insects leave ther beehives, fly on long
distance, and disappear.
149
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.5.3. Increase of activity of pathogens and parasites in the specific conditions of high insect
host density
2.5.3.1. Ever-increasing accumulation in populations of the inapparent form of infection
resulting in decrease of body weight
2.5.3.1.5. Spontaneous or winter mortality of embryos
This effect concerns the phenomena of "unhatching of larvae" known in insect defoliators. In
particular, such a case was recorded by H.A. Bess (1961), who observed mortality of one third of
embryos of Porthetria dispar in spite of winter temperatures were close to yearly average.
Consider the conditions, in which the effect 2.5.3.1.5."Spontaneous or winter mortality of
embryos" operates.
It is common in populations of Porthetria dispar in the W.C. Cook’s zone (a). This is an area
of distinctly continental climate, and the ecosystems are very disturbed by people, so that activity
of parasites is negligible, and possibility of the "horizontal" spread of infection is negligible too.
Therefore, infection spreads by the "vertical" (transovarial) way. It accumulates in the population
as the inapparent form, and it results in mortality in the embryo stage.
Such phenomena were recorded by P.M. Raspopov and P.M. Rafes (1978) in the
Chelyabinsk Region (Russia). In fall of 1967, mortality of the embryos was 57%, in fall of
1968 – 96%, and in spring of 1969 - 99.76%.
The operation of the effect 2.5.3.1.5. does not exclude the operation of the effect 2.5.3.1.4.
"Mass mortality due to affection by the acute form of infection and parasitization." In fact,
summer of 1969 occurred to be rather wet in the above-mentioned area. This weather induced
mortality of the rest of population due to acute form of infection and noticeable parasitization.
Although, density of the affected population was Low before the mortality, this affection should
be considered as an effect of CESPPs 2.5. "Effects of crowding", because the population was
overloaded by the inapparent form of infection due to High density in preceding years. Here, it
took place a cooperation CESPPs 2.5. with CESPPs 2.3.3. "Weather stresses close to common
(rains, droughts) in the period of development of post-embryo stages." Its effect is 2.3.3.1.
"Mortality under effect of the acute form of infection in the stages of larvae, pupae, and adult."
Yu. P. Kondakov (1963) also observed low percentage of larval hatching in old Porthetris
dispar infestation spots. Because healthy populations of this species possess by developed frosthardness (they are able to survive at winter temperatures 30°C below zero even if they hibernate
above a snow cover), this scholar supposed that the mortality was an effect of affection by the
polyhedrosis.
At last, mortality of Porthetria dispar embryos has been recorded by A.V. Ilyinykh (2002) in
an outbreak arising due to immigration. In the central part of the infestation area, 1-2 years after
appearing of the pest, hatching of the larvae in spring was lowered up to 22%. In a periphery of
the infestation area, high mortality of the embryos was observed on 3-4 years. This population
emigrated from old infestation spots. This fact allows supposing that the population was loaded
by infection of the slow form.
Both of the above cases concern Siberia, i.e. the areas of distinctly continental climate, where
activity of the parasite-pathogen complex was weak that impedes a burst of the acute form
infection.
In Porthetria monacha, dependence of mortality of embryos on population density was noted
by K. Escherich (1911). Further, A.I. Il’insky and I.V.Tropin (1965, p. 242) recorded mortality
of overwintering eggs of this species at severe frost. The outbreaks arise in forest articenoces
with low activity of parasites. Probably, this is a cause, which precludes affection of the
populations by the acute form of infection.
The same effect takes place in areas of mild climate, but in defoliators of the guilds, whose
traits promote accumulation of inapparent forms on infection in populations. Here are some
examples.
150
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
A.I. Vorontsov (1978, pp. 133-139) reported about a decline of lasting outbreaks of the earlyspring guild of oak defoliators – Tortrix viridana and its satellites under impact of severe frost,
which killed their embryos. Such mortality usually is referred to as "freezing out."
Although these studies were conducted in the area, where cool and prolonged rains are
common (the Moscow Region, Russia), defoliators of the guild are able to evade from their
effects due to very short duration of the larval stage. These ecosystems were disturbed heavily by
people, so that activity of parasites in them was low. Thus, these conditions were favorable for
accumulation of the inapparent infection in the populations.
Hardness of a herbivore population to severe frost can be very high if this population is
healthy. Such data are available for the apple ermine moth, Hyponomeuta malinellus Zell. In
winter 1963-1964 in the eastern part of Ukraine, air temperature dropped to 32ºC below zero.
Nevertheless, in spring of 1964, 95% of the embryos produced larvae (Degtyaryov, 1966a).
Perhaps, this population was free from the slow form of infection.
In all the above cases of high mortality, one may suppose an operation of the effect 2.5.3.1.5.
"Spontaneous or winter mortality of embryos." The effect is able to operate independently or in a
cooperation with CESPPs of the category 2.3.1. "Low ambient temperatures at hibernation even
if they are not extraordinary ones." Its effect is 2.3.1.1. "Unhatching after hibernation."
2.5.3. Increase of activity of pathogens and parasites in the specific conditions of high insect
host density
2.5.3.1. Ever-increasing accumulation of the inapparent form of infection resulting in
decrease of body weight
2.5.3.1.6. Mortality due to inadequate behavior
Such phenomena have been observed in the specific conditions – at rearing of insects, where
it is practiced a culling of individuals affected by the acute form of infection.
In fact, B. Klatt (1944) reared a line of Porthetria dispar in a laboratory over a number of
years. He found out that during several years after the beginning of this study, behavior of the
insects was quite normal. Thereupon, it appeared strange habits indicating a degradation of the
experimental population. It was observed refusal from food, cannibalism at abundant food
supply, and mortality due to unclear causes.
In the similar experiments conducted by L. Ren (1930) with the Colorado potato beetle,
Leptinotarsa decemlineata Say, the same habits were observed.
Both above cited scholars explained a degradation of the experimental insects by inbreeding.
The author proposes another explanation; this is a result of affection by the slow form of
infection in the conditions, where this form cannot to transform in the acute one.
In insect defoliators, if affection by the acute form of infection is delayed due to some
circumstances, one may suggest deviations from normal behavior. In this context, it should cite
W.G. Wellington (1960), who observed at High density of the western tent caterpillar,
Malacosoma pluviale Dyar. significant percentage of slowly moving caterpillars and weakly
flying moths.
The inadequate behavior of vertebrate herbivores at High density implies an operation of
such a response on their density in nature. In particular, at mass migrations, animals neglect a
danger that leads to heavy mortality of them.
The danger of accumulation of the slow form of infection in the conditions of weakened
natural selection might be supposed in the human society. The progress of civilization leads to
suppression of epidemics, i.e. the acute form of infection has underwent elimination. Advances
in social protection and medicine provide survivorship at contagious diseases for nearly all
peoples in developed countries, so that intensity of natural selection has become insignificant.
However, the slow and latent forms of infection occurred to be out of control, and would
accumulate in a human population as a hereditary load. This problem endangered advanced
civilizations long since. In nowadays, the trend of decrease natural selection in human society
has strengthened radically, whereas crowding is ever-increasing. Therefore, it should draw
151
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
attention to a special kind of pollution, namely: a pollution of the gene pool of a human
population, and to search for ways to clean the gene pool.
Indeed, up to 50 million of viral particles can be contained in single cell of a human body,
while the signs of any diseases are absent. However, such a load hardly to be negligible for
vitality of a host organism.
It seems this phenomenon is common for any animal and plant population, when the press of
natural selection on it becomes weakened. In fact, crop cultivars undergo eventually degradation
being affected with the virus or virus-like infections. In a result, their productivity decreases up
to twice while the signs of any disease often absent. In such cases, artificial selection is able to
restore the former advantages of a cultivar.
2.5.4. Fluctuations of herbivore host resistance to pathogens and parasites as well as
virulence of pathogens and aggressiveness of parasites
The next step in this discourse is to consider interrelations among above organisms in
dynamics taking into account as much as possible the operating factors. So, consider the scenario
with the following players: a population of defoliator Porthetria dispar, as an example, and other
species if this needs for understanding of the situation, pathogens, particularly the polyhedrosis,
parasites (their activity as factors of direct mortality and vectors of pathogens), and weather
situation. This scenario is suggested for the W.C. Cook’s zones (a) and (b) in the ecosystems of
the level ESPPs 3.3. "Late control", where activity of parasites and predators of defolators is
suppressed heavily usually by human activity.
An outbreak of Porthetria dispar in an ecosystem has recently declined. Only few insects of
this species have survived in such an ecosystem. The resident population of Porthetria dispar
underwent significant changes not only in its density, but also in resistance to the parasitepathogen complex. Its resistance has increased in a result of severe selection by this complex, but
infection retains in the population.
The presence of the polyhedrosis in the rest of population after the decline has shown for
Porthetria monacha (Bakhvalov et al., 1988). During several succeeding years this population
continues to clean from insects with any form of infection. The innocuous phase in Porthetria
dispar population dynamics continues up to five years. M.G. Khanislamov et al. (1958, p. 24)
reported that drought or severe winter in year of a decline of a Porthetria dispar outbreak as well
as in the following year did not induce a new outbreak. An onset of the appropriate weather
situation, i.e. drought and/or severe winter, served as a releaser of the next outbreak, on
condition that such a weather situation took place no less than two years after the decline.
The drought in May-June, especially two seasons in succession on the second year after the
decline and later, and the severe winter exert the following effects:
i) Suppression of parasites and other vectors of infection, so that a spread of infection within
a population is stopped.
ii) Direct mortality of insect hosts due to parasites and predators becomes insignificant.
iii) Insect hosts having the inapparent form of infection are eliminated by the weather
situation unfavorable to the insects.
A growth of the population begins shortly after the drought and/or severe winter, but at the
starting point, the density is so Low that first sings of defoliation appears on the third year after
onset of this situation (Khanislamov et al., 1958, p. 14). The fourth and fifth years are a
culmination of an outbreak or the eruptive phase, and the sixth is a decline of this outbreak, so
that an outbreak of Porthetria dispar continues six years (Ibid., 14).
These events take place if drought in May- June in the period of outbreak is absent. At onset
of drought in the outbreak phase, an outbreak continues 10 years (Ibid., pp. 22-23). This delay
might be explained by suppressive effect of the drought on vectors of infection and the rapid
desiccation of diseased larvae, which unable to serve as a source of infection.
152
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
The duration of the phases is true for the area wide-outbreaks as whole. As to a given
ecosystem, High density of Porthetria dispar in Bashkiria keeps usually one or two seasons.
After that the insects emigrate in other plots, where the density is less, if any.
With the increase of population density, it grows its affection by pathogens, firstly in the
slow form. The data by R.W. Campbell (1963a, 1978) give grounds for such a suggestion. In
fact, when defoliation reaches only 5%, weight of female pupae begins to decrease.
The higher density, the wider pathogens spread in a population, the greater percentage of the
insects is affected by the acute form of infection. The intensity of this process depends on not
only host density, but also on activity of pathogen’s vectors. In turn, their activity depends on
structure of ecosystems and weather situation.
In a pathogen population, it presents strains of diverse virulence. The ratio of them in diverse
circumstances is unequal. At growth of host density, the strains of more and more virulence have
advantage. Indeed, let a host insect was inoculated a mixture of strains with diverse virulence. It
would be affected by the strain of highest virulence, whereas the rest of strains will be eliminated
in a competition within its body. Such a diseased insect serves as a source of the most virulent
strain, which has the best chance to inoculate other insects. This is a similarity of “passage” of
pathogens in the laboratory conditions that leads to an increase of their virulence.
Simultaneously with increase of pathogen virulence, it grows activity of parasites, which
have abundant insect hosts and sufficient imaginal feeding if weather situation becomes milder.
Therefore, it grows the role of parasites as direct mortality factors and vectors of pathogens. At
the decline phase, activity of the both mortality factors reaches a maximum that results in a
decrease of host insect population to Insignificant density.
After that, it begins a reverse process – the cleaning of insect host population from infection
in the conditions of Insignificant density. As to the parasites, they probably nearly distinct in an
ecosystem after the decline of an outbreak, because the rest of host insect population acquires
resistance to them due to intensive selection pressure at the decline.
The insects affected by strains of high virulence die quicky. Therefore, in the conditions of
Insignificant density of insect hosts, where vectoring of infection is of low probability, the
strains of high virulence disappear, whereas the attenuated strains have better conditions for
survivorship and spread in a host population.
This change of virulence depending on host density was shown in the case of the
myxomatosis epizootics in rabbit populations in Australia and Britain, where the attenuated
strain of the virus was recorded in several years after sharp decrease of host density (Deacon,
1983, p. 28).
The above discourse shows that Insignificant density is a means of cleaning of a population
of insect defoliators from pathogens. In other words, Insignificant density is an obligatory
payment for High density. At such a density, a population of defoliators becomes clear from
pathogens, because spread of them is nearly impossible.
In this context, it should cite the review by S.S. Izhevsky and P.M. Belyaev (1984), where it
was considered the consequences of total treatments of ecosystems with insecticides. The
treatments decrease density of defoliators to Insignificant level. In a result, pathogens disappear,
and due to the sanitation of a herbivore population, a new increase of its density becomes to be
possible.
In the conditions of ESPPs 3.3. "Late control", population dynamics has a character of
oscillations or a distinct cyclic nature. The term "cycle" is used here in the sense proposed by
D.E. Davis (1957, p. 163), namely: "In ecological usage the term "cycle" refers to a phenomenon
that recurs at intervals. These intervals are variable in length, but it is implied that their
variability is less than one would expect by chance and that reasonably prediction can be made."
The studies by M.G. Khanislamov et al. (1958, pp. 24-25) demonstrate the cycles of
outbreaks of Porthetria dispar in Bashkiria for the period of nearly 100 years – from 1860-ies to
the middle of 1950-ies. The nine outbreaks took place over this period. The intervals between the
decline of an outbreak and the beginning of the outbreak (eruptive) phase of the next one
constitute the following row: 12, 14, 11, 10, 10, 10, 8, and 11 the number of years.
153
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
As one may see, the average value of this row is close to 11 years. The interval between the
outbreaks, which equals 11 years, is a period that necessary for completion of the
microevolutionary process of arising of the population, which is resistant to pathogens.
In other areas, variations as to the interval between outbreaks are wider, as follows: in Europe
- 5 - 13 years (Schedl, 1936, p. 50), 9 years in the Crimea Peninsula, Ukraine (Chugunin, 1949),
V.I. Benkevich (1962a, p. 22): “In East Siberia, periodicity of gypsy moth outbreaks is 20 to 25
years,” 5 - 6 years in the Low Dnieper area, Ukraine (Zelinskaya, 1988), 6 – 8 years in the
Russian Far East (Chelysheva and Chelyshev, 1988), or 3 – 6 years for the same area
(Chelysheva, 1988), 18 years in the Tula Region, Russia (A.I. Il’insky, pers. comm.). The latter
Region is situated on the north-west border of the W.C. Cook’s zone (b).
How does to explain the deviation of the interval comparing with the period close to
11 years? The shortage of this period to a few years might be due to returning of the infestation
spot in the same forest plot, rather than the arising of a new outbreak. In Asia, migrations at High
density are well expressed in Porthetria dispar. It should not confuse a true outbreak that spreads
on vast areas with migrations of small infestation spots that appear here and there. Such a
situation is common in durable area-wide outbreaks in the conditions of the distinctly continental
climate.
Further, the short intervals might be related with recurrence of High density in few years after
suppression of an infestation spot by insecticide treatment. If the treatment is conducted in early
of the outbreak (eruptive) phase, when a population is rather healthy, the density can restore on
the second or the third years after the treatment (P.M. Rafes, pers. comm.).
At last, in areas close to north border of the W.C. Cook’s zone (b), weather situation
favorable for arising of Porthetria dispar outbreaks occurs rarer than that in southern areas of the
zone. In the northern areas of the zone (b), the interval is longer. This is the case of the Tulle
Region (Russia), where it has been recorded the duration of the interval equals 18 years.
The periodicity of Porthetria dispar outbreaks in some areas is close to 11-years cycle that
gives the grounds for some scholars to suppose the impact of solar activity, which has the same
average periodicity. This question was considered thoroughly by M.G. Khanislamov et al. (1958,
pp. 24-25). They cited K. Schedl (1936), who studied the periodicity of Porthetria dispar
outbreaks in Europe and North America for 1720- 1935. According to this scholar, in some cases
10-11-years systematic periodicity can be noted if the selection of these reports was not
sufficiently scrupulous.
The idea that solar activity predetermines cyclic character of the population dynamics would
has good grounds if one would prove that a given phase of it coincides with a particular phase of
solar activity. However, M.G. Khanislamov et al. (1958, p. 24) showed an absence of such a
coincidence over nearly the 100-years period. The outbreaks of Porthetria dispar in Bashkiria
began at diverse phases of the solar activity. This is not surprising, because the beginning of an
outbreak is under strong impact of appropriate weather situation, whereas the latter does not
depend on the solar activity. Droughts in May-June and severe winters occur without any
regularity. Further, the periodicity of the solar activity is even less regular than that in population
dynamics of Porthetria dispar. The intervals between phases of maximum of the solar activity
vary in the range of 7 – 17 years, while the intervals between the outbreak phases vary in the
range of 8 – 14 years (in Bashkiria).
Nevertheless, the effect of the solar activity indeed takes place, but it determines a scale of
outbreaks, rather than frequency of their arising. In the period of maximum the solar activity,
excited areas of the solar surface irradiate ultra-violet rays approximately sixty times greater than
equal areas do at the common activity (Eigenson, 1963). High level of irradiation of the earth
surface at maximum of the activity induces hereditary variability in insects. Therefore, it appears
more populations, in particular Porthetria dispar, with high resistance to pathogens. This is so
because increased solar irradiation intensifies mutations within insect populations.
Such a supposition is based on the studies by V.I. Benkevich (1984, p. 21). He stated that for
arising of outbreaks of this species is sufficient a combination of drought in May-June, especially
two seasons in succession, and severe winter in the same year or one/two subsequent years. But
154
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
if such a weather situation is combined with a maximum of the solar activity (in close years), the
areas seized by a Porthetria dispar outbreak became much more than those in at the period of the
quiet Sun. At coincidence of appropriate weather situation with high solar activity, it is increased
the number of Regions in the European part of Russia, where the outbreaks are recorded.
The population dynamics of Porthetria dispar becomes more complicated due to migrations
of these insects on large distance that supplies ecosystems with populations having extremely
high resistance to pathogens. The source of such populations is situated in southeastern parts of
Europe (Bashkiria) and adjacent areas. Here, the environmental conditions constitute the
ecological optimum for Porthetria dispar. They include distinctly continental climate, disturbed
structure of ecosystems that radically decreases activity of entomophagous organisms, and the
very simplified system "an insect host – its enemies." Among the enemies, pathogens
particularly the polyhedrosis are most active. Therefore, microevolutionary process of mutual
selection in this system becomes maximally expressed that results, in one extreme, the highest
resistance of a Porthetria dispar population, and, in another extreme, the highest virulence of the
pathogen.
To define such a simple system might be used the term "sea-saw." This children’ play is a
mechanical model of the situation, where diversity of interacting species in an ecosystem is
simplified to minimum.
The events are developed in such a way. In the southeastern areas, it arises the appropriate
weather situation. Its effect might be intensified by increased solar activity. In a result, outbreaks
of Porthetria dispar burst. When density of the insects becomes High, they leave affected
ecosystem by migration in the stages of neonate larvae or butterflies. In these populations, both
males and females are able to fly on large distance. The migration is facilitated by mighty dry
and hot wind of northwest direction ("sukhovey" in Russian), which occur often in East Europe
in May.
A.I. Vorontsov (1978, p. 127) has supposed that area-wide outbreaks of diverse species of
oak defoliators have a migration character. As an example, he noted the grandiose outbreak of
Porthetria dispar in East Europe in 1950-ies. It started in 1951 in the extreme southeast, and up
to 1957-1958, it spread in northwest direction to the Moscow and Kalinin (now the Tver)
Regions.
The migrational character of the outbreak in these Regions is obvious. A.I. Il’insky (1959)
observed mass appearing of the butterflies after the mighty wind of northwest direction, whereas
G.N. Gornostaev (1962) recorded attraction of the females on a mercury lamp. A flight of the
female on long distance is characteristic for Asian and Bashkirian populations of the species. The
capacity of Porthetria dispar to disperse is characterized by the fact that in 1959 nine females of
this species were found out in Finland.
The areas in vicinity of the border between Europe and Asia serves as a hotbed of healthy
(aggressive) populations of Porthetria dispar and other species of defoliators, alike the south
China is a hotbed of high virulent strains of the influenza.
The next step is to consider possibility of operation of microevolutionary process in
maintenance of ESPPs to the nun moth, Porthetria monacha. This species is close relative of
Porthetria dispar, but pattern of population dynamics of them is quite different. The conditions,
which determine development of outbreaks of Porthetria monacha, have been considered
thoroughly by M.G. Khanislamov, N.K. Latyshev, and Z. Sh. Yafaeva (1962). Beside own data,
these scholars generalized the 102 scientific reports on this problem.
The attempts to find the dependence of the outbreaks on weather situation over all the species
range gave rather inconsistent results. The analysis of meteorological data in Bashkiria for 1936
– 1960, when two outbreaks of Porthetria monacha took place, showed that emergence of the
population from the innocuous phase occurred in the years with increased precipitation in the
first two months of a season and increased sum of negative temperatures in the beginning of
winter. The succeeding growth of the density was determined by warm and dry weather in May
over three years in succession. In this article, the scholars supposed that it is hardly to explain the
effect of weather situation.
155
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
But in further publications, they stressed the role of abundance of staminate "flowers" in
host-trees that was determined by appropriate weather (Khanislamov and Latyshev, 1962;
Latyshev, 1968). Porthetria monacha in Bashkiria tended to reach Higher density in wet habitats
– ravines, lowlands, and lower parts of slopes. These habitats were defined as the reservations,
where moth’s density was 20-30 times higher than that outside.
The role of Antibiosis of host-trees – Pinus silvestris is obvious. The survey showed that in
the reservations, the species was present on all the pine trees, but on suppressed ones, its density
was much greater. Outside of the reservations, it was found out only on suppressed trees.
The affection was recorded only in pine stands, although, according the data of a number of
scholars, at rearing, the larvae feed normally by all the common deciduous and coniferous tree
species.
As to natural enemies of Porthetria monacha, it is noteworthy insignificant parasitization of
it in Bashkiria, and heavy affection at a decline of an outbreak by the polyhedrosis. This fact as
well as the data of H. Gäbler (1952) on ever-increasing participation of darkly colored variations
in populations of this species over several decades imply the important role of fluctuation of
resistance to the polyhedrosis in the population dynamics.
It seems, the peculiarities of population dynamics of this species are determined by such a
trait – its optimum is in the conditions of the wet environment. In it, staminate "flowers" present
during longer time. But such conditions are favorable for affection by the polyhedrosis.
Therefore, arising of the outbreaks is possible on condition that a population of the species
acquires very high level of resistance to this pathogen. Again, it is possible in a result of
microevolutionary process, which, however, needs a longer term comparing with that in
Porthetria dispar. Therefore, frequency of outbreaks in these relative species is unequal. In fact,
in Russian Far East, according observations in 1960-1980-ies, outbreaks of Porthetria dispar
repeated with intervals six-seven years, whereas an outbreak of Porthetria monacha was only
one, and previous outbreak of this species was sixty years ago (Chelysheva and Turova, 1985).
In conclusion, it should cite the views of some scholars, which have given by
M.G. Khanislamov, N.K. Latyshev, and Z. Sh. Yafaeva (1962, p. 8). Thus, N. Stark (1931) has
supposed that Porthetria monacha is "a stumbling stone of forest entomology." Further,
according to V.I. Plotnikov (1951), "It is quite incomprehensible, why some mass pest insects,
for example the nun moth, …after long absence suddenly during two-three years exert
devastation, and after that disappear without leaving a trace."
As to Porthetria monacha, such judgement is valid even now. Nevertheless, the knowledge
of CESPPs 2.5.4. "Fluctuations of host resistance to pathogens and parasites as well as virulence
of pathogens and aggressiveness of parasites as well as virulence of pathogens and
aggressiveness of parasites" opens some prospects for understanding of this problem. It seems
the microevolutionary process in Porthetria monacha is complicated by the fact that its
population needs not only to acquire resistance against pathogens, but also to acquire some
resistance to protective products of coniferous host-trees – oleoresin. Even in weakened trees,
oleoresin exerts the protective effect. Natural selection under the effect of these factors results in
appearing of a resistant population over the prolonged period of several decades. In addition, it is
need an onset of weather situation, when CESPPs 2.1.2.1.1. "Superevasion from herbivores"
does not operate. It takes place at abundant appearing and longer presence of staminate
"flowers." That is why the innocuous phase in population dynamics of Porthetria monacha is
much more prolonged than that in defoliators of deciduous tree species.
In this context, it should mention the cases of affection by Porthetria dispar of coniferous
tree species. It occurs much rarely than the affection of deciduous tree species. It seems in the
both cases, the same microevolutionary process takes place.
The process encounters with another obstacle, namely: developed Antibiosis of coniferous
host-trees. Population of the both Porthetria species are able to reach High density on condition
that the most part of a stock of dominants has decreased Antibiosis – CESPPs 2.1.1.2.1.2.1.
"Antibiosis to herbivores, Physiological (biochemical), Permanent."
156
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
In rodent herbivores, in particular in the lemmings, a recurrence of outbreaks has surprising
regularity. This is so because CESPPs operating against these animals are extremely limited. In
the lemmings, neither resistance of host-plants, nor activity of predators can suppress them. Only
pathogens fulfill the suppression, rather that abundance of blood-sucking insects provides wide
possibilities for vectoring of infection. Affection of the populations by infection takes place
before the food resource gets exhausted. Therefore, the effect 2.5.1.3.2.2. "Decrease of body
weight and fecundity" is insufficient to significantly decrease density. The effects 2.5.3.1.4.
"Mass mortality due to affection by the acute form of infection", and 2.5.3.1.6. "Mortality due to
inadequate behavior" are the main.
The activity of these effects provides an operation of the "sea-saw mechanism" in its clearest
performance.
It is obvious that the present view holds by the course of the ideas of A.J. Lotka (1925, 1934),
Volterra (1927, 1927a, 1931, 1931a, 1933, 1937), V. Volterra and U. Dancona (1935) and
D. Pimental (1961, 1961a, 1963, 1963a, 1964, 1968). Nevertheless, it seems a novel feature has
been advancing now. The view stresses that violent fluctuations of herbivore density take place
on condition that ESPPs is disturbed mainly by human activity, or in the specific environment as
in the Tundra and Desert biomes. Contrary, at high level of ESPPs, mighty and numerous
CESPPs dump the fluctuations to minimum.
As to insect defoliators of deciduous tree species, which are protected by CESPPs 2.1.1.3.1.2.
"Tolerance to herbivores, Repair or compensation of losses of host-plant tissues", and well
developed prerequisites of CESPPs 2.2.1."Natural enemies of invertebrate herbivores" determine
not only high activity of natural enemies, but also rich fauna of defoliators. In such conditions,
fluctuations of pathogen virulence are minimal. With the exception of the early-spring guild of
defoliators, density of any species does not reach High level. Competition among species within
an ecological niche (within a guild of defoliators) is not expressed significantly. This promotes to
increase of species diversity within a niche. It might be this effect is a cause, why the "principle
of competitive exclusion" operates well in the laboratory conditions, but it is impotent in nature.
There exist two explanations of periodicity of defoliators’ outbreaks, particularly Porthetria
dispar, namely:
1. Fluctuations of pathogen’s virulence within a population of defoliators due to the genetic
feed-back mechanism in the ecosystems of the level ESPPs 3,3.”Late control”,
2. Fluctuations of affection of the pathogens due to difference in presence of the infection in
outer media as to a population of a defoliator.
The former may be seen above. The latter is shown in the following words: “The hostpathogen system is complicated by long stages during which the pathogen exists in the external
environment, protected from ultraviolet degradation by the soil of temperate forest” (Wallner,
1987, p. 329).
These words might be understood as follows: an outbreak of Porthetria dispar arises, when
ultraviolet rays kill infection in the soil. When the infection in the course of acumulation in the
external environment of an ecosystem reaches some value, the outbreak undergoes a decline.
Further effect of ultraviolet rays kills the infection in the soil that allows Porthetria dispar to
begin a new outbreak.
On the same page (W.E. Wallner, 1987, p. 329), it is cited the scholars, who shore this view:
R.M.Anderson and R.M. May (1980), who analyzed the data for twenty-eight species, R.M. May
(1983), and L.M. Zelinskaya (1980). It should add to this review the reports of Ya.V. Chugunin
(1949. 1958).
157
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.5.4.
Fluctuations of herbivore host resistance to pathogens and parasites as well as virulence of
pathogens and aggressiveness of parasites
2.5.4.1. Suppression of defoliators over the period, which provides a reprieve
for restoring of vitality of dominants
An operation of the "sea-saw mechanism" determines existence the period, when density of
defoliators (insects and vertebrates) keeps on Insignificant level. The duration of this period is
close to a decade in the case of Porthetria dispar or more, and to a few years in the case of the
lemmings. These terms are sufficient for dominants to restore their vitality if they have
developed Tolerance to herbivores.
Ph. M. Wargo (1981, pp. 242-243) reported for Porthetria dispar: the following: "Trees can
recover. …This process may take as many as 10 years. Campbell and Sloan (1977) observed that
after a single heavy defoliation, the number of good crown trees declined over a period of
5 years and it was another 5 years before the number of good crowned trees returned to their
conditions prior to the defoliation. Obviously, if defoliation is repeated, the amount of
deterioration will increase and hence the length of time to recover."
In the Russian literature, mortality due to heavy and repeated defoliation by Porthetria dispar
has been recorded only in suppressed trees within oak dominants. As to the main stock of
dominants, the defoliation resulted in a decrease of stem increment (no more than on 50%) over
several years beginning with the outbreak phase. After that, the increment increased, and the
losses were partially compensated.
In particular, this phenomenon was studied by A. Yu. Paramonov (1934) in the Crimea
Peninsula (Ukraine), for the period 1909-1932; M.S. Greze and V.L. Tsiopkalo (1936) in the
central part of Ukraine for the same period; and A.I. Il’insky and A.I. Kobozev (1939) in the
Voronezh Region (Russia) for 1920- 1936. The compensation is explained by enrichment of the
soil due to entering into it the easily mineralized products of the defoliation.
The decline of oak stands is often accompanied by Porthetria dispar defoliation, but the
latter is not considered by above-mentioned scholars as a primary cause of tree mortality. The
main cause of the decline is considered as general suppression of dominants due to impacts of
droughts and severe winters. Lately, the same conclusions were repeated by A.I. Il’insky (1959).
D.F. Rudnev et al. (1975) added to this view that forest decline observed in the context of
outbreaks of defoliators is determined mainly weakening of dominants due to improper
silvicultural practices.
Summing up, the role of the effect 2.5.4.1. "Suppression of defoliators over the period, which
provides a reprieve for restoring of vitality of dominants" is great in the environmental
conditions, where climate nearly annually is favorable for growth in defoliator’s density to the
High level, and host-plant resistance is unable to preclude growth of the density, i.e. here it
operates CESPPs 2.1.1.3.1.2 "Tolerance to herbivores, Repair or compensation of losses of hostplant tissues." Then, an operation of effect 2.5.4.1. allows these host-plant to restore their
vitality. If the effect 2.5.4.1. would not operate, they would die off. Because the host-trees are
dominants, such an ecosystem undergoes a decline.
In the Tundra biome, partial consumption of dominants by the lemmings is beneficial for
maintenance of general stability of this ecosystem, because the consumption intensifies recycling
of nutrients. This is important in the conditions of slow turnover of substances. In spite of
frequent outbreaks of the lemmings, vegetation in the tundra thrives until human intervention
with overgrazing by the reindeers disturbs the general stability of this ecosystem.
2.5.5. Disturbance in the media of inhabitation
High density of herbivores brings changes in their environment. In some cases, these changes
result in affection of a population by pathogens or lay obstacles for further development.
158
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.5.5.1. Affections by pathogens due to deterioration of sanitary state of the media
The mealybug, Pseudococcus njalensis exerts serious damage of host-trees, when the
symbiotic ants Crematogaster sp. cleaned its colonies from saccharine exudates of these sapsucking insects. If the ants were controlled, the exudates accumulated, and served as a media for
bacteria and mold fungi, that resulted in suppression of mealybug, and a decrease of damage on
cocoa trees; then, it disappeared the virus disease of the cocoa trees transmitted by the mealybug
(Hanna et al., 1956).
When density of the aphids reached High level in the conditions of insignificant activity the
symbiotic ants, aggregations of the aphids become covered by sticky saccharine exudates that
provokes affection of their by fungal pathogens. This effect was observed by Ya. V. Chugunin
(1959) in forests in the Crimea Peninsula (Ukraine) affected by the aphids Dysaphis mali Ferr.,
D. pyri B. d F. and others.
2.5.5. Disturbance in the media of inhabitation
2.5.5.2. Mortality due to appearing of obstructions for further development
When studying population dynamics of Hyponomeuta malinellus, A.S. Nekhay (1983, p. 29)
noted the cause of its mortality specific for High density. If the number of the pupae per web nest
reached several hundreds, the butterflies situated in a central part of a nest were unable to leave
the shelter and died.
2.5.6. Exhaust of adequate food
2.5.6.1. Mortality due to starvation or inadequate food in the same generation or in the next
one, decrease of fecundity
An operation of this CESPPs is probable in the case of outbreaks of exotic species, when
activity of resident natural enemies is very low. Mortality due to starvation in a current
generation, and low vitality of progeny of survived individuals serve as the main restriction of
population growth.
Operation of CESPPs 2.5. "Effects of crowding" in phytopathogens
J.E. Van der Plank (1975) has offered the data, which suggest an operation in phytopathogens
the phenomena analogous to CESPPs 2.5.1. "Deterioration and/or shortage of food" in
herbivores, as follows:
"The effect of antagonistic interactions between spores: as inoculum increases disease
increases to a maximum and then decreases. Fig. 1.3. is based on data Davidson and Vaughan
(1964, p. 3 and Fig. 1.4.). It shows the effect of antagonistic interaction between uredospores of
Uromyces phaseoli. Bean leaves were inoculated with suspensions of spores, and after
appropriate inoculation the number of lesions was counted. Figure 1.3 relates the number of
lesions to the number of spores per cm² of leaf surface. With increasing of inoculum, the number
of lesions increases to a maximum of about 27 lesions per cm². Thereafter, with still further
increases of inoculum, the trend is reversed and the number of lesions decreases, fewer lesions
being formed by 3400 than by 1100 spores/cm².
Self-inhibition of germination seems to be common in the uredospores of the rust fungi
(a number of authors). The same is true for Erysiphe graminis on barley."
Signs of the disease are directly proportional to inoculum, when the amount of inoculum is
small. (Ibid., p. 44.).
E.S. Tatarenko (1959, cited in S.A.J. Tarr, 1972, Ch. XXV) reported about parasitization of a
unit of a fungus (thallome) on another one of the same species. It is probable that parasitization
within agents of phytopathogens takes place at high concentration of inoculum.
159
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.6. HUMAN CONTROL MEASURES
This category of CESPPs embraces all the kinds of control measures used by people. They
are shown in the vast special literature. In particular, the brilliant review has been offered by
E.F. Knipling (1979). The control measures will be considered in the Sections 3(1), 6(1), and
8(1) in the context of patterns of their operation and relevance at maintenance of ESPPs.
160