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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
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AXIOM 3(1) The LEVELS of ECOSYSTEM STABILITY to PLANT PESTS and
the CATEGORIES of BIOMASS of DOMINANTS
BIOCENOSES
The level ESPPs 3.1. Proper control
There exist ecosystems, in which outbreaks of PPs have never been recorded. As to insect
herbivores, it has been noted by Ch.S. Elton (1958, Ch. 8), and F. Schneider (1939, cited in
D. Pimental (1961a). These reports concern the tropical rain forests, i.e. for the conditions of hot
and wet climate, in particular with weakly expressed season’s differences. Such conditions are
favorable for realization of species potential of invertebrate herbivores having many generations
per year, and for aggressiveness of phytopathogens. Nevertheless, epiphytoties also have not
been recorded there.
In such ecosystems, the herbivores have been kept on the level below threshold of damage
over unlimited time that suggests high efficacy of CESPPs in such forests. Also, it should pay
attention on the mild effect of them – they do not allow an extinction of the herbivores in such
ecosystems. Contrary, tropic forest ecosystems are known by richness of their fauna of insect
species.
As to forest ecosystems of the temperate climate, the facts of their high level of ESPPs have
been presented in literature a little. Consider some examples of such situations.
Defoliators of evergreen coniferous tree species
In Ukraine, in vicinity of Kyiv, there exist ecosystems with the following characteristics: in
an upper story, the Scots pine, Pinus silvestris of 80-200 years old, in a lower story, the English
oak, Quercus robur of various age, a dense undergrowth (a shrub stratum) with the hazel, hawthorn, mountain ash and other shrubs and small trees. These forests grow in habitats optimal for
pine. They are mainly of natural origin, although some of them are planted. If destructive
impacts of human activity in them are minimal, physiological state of all the vegetation is high,
so that CESPPs of the categories 2.1.1.1."Nonpreference", 2.1.1.2. "Antibiosis ", and 2.1.1.3.
"Tolerance" are effective. Further, because prerequisites of CESPPs 2.2.1. "Natural enemies of
invertebrate herbivores" are well developed, activity of natural enemies of herbivores is the best.
In these ecosystems, in the dominants (the pine), neither outbreaks of herbivores, nor
epiphytoties of phytopathogens have been known.
Moreover, at mass immigration of insect herbivores, they stay free from even Low density of
these pests. In particular, the immigration took part at the end of 1970-ies and beginning of
1980-ies, when the vast areas in the western part of USSR were seized by a mass outbreak of the
nun moth, Porthetria monacha. In that period, in the above-mentioned stable forest ecosystems,
any signs of defoliation were not seen. Although sticky traps with the attractive pheromone of
Porthetria monacha – disparlure captured up to several dozens of the moth’s males per trap
(M.M. Zavada, pers. comm.). Hence, the moths immigrated in the stable stands in the noticeable
number, but they were unable to produce even Low density.
The capacity of active CESPPs to suppress insect defoliators at mass immigration of them
has been proved experimentally.
V.I. Grimal’s’ky (pers. comm.) failed to establish of an outbreak of Dendrolimus pini in
stands of Pinus silvestris by means releasing in them larvae of this pest. It took place both in the
stands, where oleoresin exudation from the needles was high, and in the stands with decreased
oleoresin exudation, but with high activity of natural enemies of defoliators.
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
This is the level of ESPPs 3.1. "Proper control" for needle-eating defoliators in ecosystems of
evergreen coniferous tree species belonging to biomass of the category D-I.
It is naturally to put the question: how do species of needle-eating defoliators survive if hosttree Antibiosis kill them in the ecosystems with healthy host-trees? It occurred to be, in
evergreen coniferous trees, a part of needles progressively losses the properties of D-I, and goes
over the category D-III. This is a lower part of a crown in stands with closed canopy. Due to
light deficiency, these needles produce less assimilative products than they use for their vital
activity. These needles are parasitic components of a tree. In so doing, their Antibiosis
progressively decreases up to zero in the course of dying off. The factual evidences of this
suggestion are the following.
P.J. Kramer and T.T. Kozlowsky (1960, Ch. 16) reported that in the pine, a pruning up to
70% of a crown in its lower part nearly did not decrease an increment of its stems.
V.I. Grimal’s’ky (pers. comm.) found out that in pine stands with closed canopy, needles in a
lower part of a crown had insignificant oleoresin exudation.
Although density of oleoresin ducts in the pine needles growing in the light was equal to that
in the trees growing in the shade, a diameter of the ducts in the shade was less (Masyuk, 1931).
Bearing in the mind of above data, it is easily to understand, why pine needles growing in the
conditions in intensive shadow as well as senescent needles are affected usually in matured
stands by the schutte fungus, Lophodermium spp. In nurseries, on pine seedlings, i.e. in the
conditions of well lighting, but presence of the factors, which weaken the seedlings, this fungus
affects sometimes entire needles. Thus, conditions of shadow or light are insignificant for
thriving of the fungus. It is important just a deterioration of physiological state of a host-plant.
A search for foodstuff with decreased Antibiosis forces insect defoliators to develop behavior
traits, which as a whole are not typical for these insects. In fact, it is known that insect defoliators
prefer to feed in an upper part of a tree crown. This is so because in this part, foliage is more
nutritive, and insolation on an open place protects from pathogens. Nevertheless, outbreaks of
Porthetria monacha arise in closed stands, and defoliation spread from a lower part of crowns to
an upper part of them (Shevyryov, 1894, pp. 9, 29). This fact might be explained by low
Antibiosis of needles in the shadow. The needles in shadow are acceptable for older larvae of the
moth, whereas they are inadequate for neonate ones. The neonate larvae need in foodstuff free of
Antibiosis. This is staminate "flowers" filled by unripe pollen. In them, oleoresin ducts are
absent, and any signs of Antibiosis are unknown, so that they belong to biomass of the category
D-II. In addition, they are rich of nutrients.
The role of such a foodstuff for the neonate larvae and physiological state of pine host-trees
for the older larvae was shown experimentally by N.K. Latyshev (1969). When the neonate
larvae were rearing on needles of growing pine trees, their mortality exceeded 80% in the first
instar. Their survivorship to adulthood depended on physiological state of these trees. On the
vigorous trees, the survivorship was close to 1%, on the trees of intermediate state – 2%, and on
the depressed trees – up to 5%.
Contrary, at feeding of the neonate larvae by staminate "flowers", their survivorship in the
first instar was close to 100%. After three-days feeding by the "flowers", the larvae were reared
on needles in pine crowns. Then, their survivorship to adulthood was 10% on the vigorous trees,
17% on the trees of the intermediate state, and 32% on the depressed trees.
The more the period of feeding of the young larvae by staminate "flowers", the greater their
survivorship to adulthood. If they spent on the "flowers" fifteen days and after that were set on
the needles, the survivorship depending on state of the trees was 76%, 78%, and 85%,
respectively.
These data and knowledge of a situation in pine stands allow understanding of causes of the
different levels of their ESPPs as to Porthetria monacha.
In Bashkiria, the Southern Urals Mountains, where N.K. Latyshev conducted his studies in
1956-1967, "reservations" of this species, where Porthetria monacha was noticeable nearly
every year, were located in overstocked pine monocultures. Here, "flowering" continued 10-12
days. Moreover, here there was the higher ratio of male "flowers" comparing with female ones.
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Antibiosis of trees in such stands was decreased. These ecosystems concerned the category
ESPPs 3.3. "Late control." Contrary, pine stands of natural origin, where trees were widely
spaced, "flowering" completed during 4-5 days. Here, ESPPs stayed on higher level.
There exist a trait, which allows a species of defoliators to evade from host-tree Antibiosis by
means of hatching of their larvae in the period of a season, when host-tree Antibiosis is
decreased. This is characteristic, in particular for Dendrolimus pini. Its neonate larvae appear in
the middle of summer, when oleoresin exudation in Pinus sylvestris is minimal due to deficiency
of water supply. V.I. Grimal’s’ky (pers. comm.) supposes that this trait gives a chance to some
larvae to survive even in healthy pine stands.
The same trait is characteristic for the pine looper, Bupalus piniarius. M. N. RimskyKorsakov at al. (1949, p. 234) have noted, that neonate larvae of this species feed by nibbling of
riffles along a pine needle close to its surface. Nevertheless, droplets of oleoresin often exude on
a needle’s surface, and the larvae tend to crawl away them.
It takes place, however, noticeable defoliation in ecosystems of evergreen coniferous trees on
the level ESPPs 3.1. This is possible on condition that a part of needles belong to the category
biomass D-II. Such properties have young needles of the Norway spruce, Picea excelsa (abies)
L., where protective means (oleoresin ducts) is not formed yet. This suggestion is based on the
report by M.V. Glazov (1984) on values of consumption of spruce needles by insect defoliators
(larvae of butterflies and sawflies of unnamed species) in forests of the boreal and sub-boreal
types in the East Europe. In these forests, it takes place annually consumption of a part of young
needles. Values of the losses are moistly very weak – 4-5% of the total needle production.
However, in years with abundant seed yield, when production of the needles drops on 40-60%,
the values of such losses increase in two-three times. Any negative effects of the defoliation on
host-tree vitality has not been observed over the period of the studies. Moreover, M.V. Glazov
supposed the beneficial effect of the defoliation in term of stimulation of growth of near by
sprouts, and promotion of better structure of tree crowns.
The loss of old spruce needles are insignificant year after year - on the level no more than
2%. This part of tree crown belongs probably to the category biomass D-III. Both on young and
senescent needles, values of defoliator’s density are of the category Insigninicant.
Defoliators of deciduous tree species and the larch
On the level ESPPs 3.1. “Proper control”, there exist a difference between ecosystems of
evergreen coniferous trees and ecosystems of deciduous trees and the larch, Larix spp. as to
density of defoliators. In the former ecosystems, the density stays on the Insignificant level year
after year. In the latter, the density of the spring-summer, summer-fall and fall-spring guilds
stays in some seasons on the Low level reaching 30% of area of a leaf surface.
The difference is determined by the diverse categories of biomass of assimilative tissues in
above types of ecosystems. In the former, this is D-I, whereas in the latter, this is D-II.
Antibiosis in D-I ensures complete protection against consumption of the healthy needles by
defoliators. Tolerance in D-II allows consumption of leaves annually, and the Low level of
defoliation is safe for vitality of dominants.
Consider the reports about ability of ESPPs to suppress defoliators of deciduous trees. The
numerous data are available for Porthetria dispar.
R.W. Campbell and R.J. Sloan (1978) introduced into a forest plot 250 egg-masses of
Porthetria dispar per acre. In fall of the same year, density of the egg-masses occurred to be the
same as in the control, i.e. insignificant one.
K. Furuta (1982) exposed several egg-masses of Porthetria dispar on every of 29 birch stems
in a mixed forest plot, where density of this species was very Low. In fall of the same year, any
of the egg-masses were not found.
G.I. Vasechko (1990) over a number of years studied ESPPs to Porthetria dispar by means
of introduced egg-masses of this species in oak forests in vicinity of Kyiv. These forests merit
detailed characteristic, because some of them are actually unique at least for East Europe.
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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 this area, it has been retained plots of oak forests established beginning with the middle of
XVII century. The age of Quercus robur is evaluated as reaching no less than 300 years. These
forest plots have a multistory structure and a wide diversity of plant species. Outbreaks of
Porthetria dispar and other species of spring-summer guild of oak defoliators have not been
recorded here. On the other hand, outbreaks of the early-spring guild of oak defoliators are
common here that, however, does not preclude prosperity of the forest plots.
Exposition in these stands of egg-masses of Porthetria dispar in the numbers sufficient for
complete defoliation many trees did not resulted in defoliation. Density of the species was not
increased comparing with control that was shown by exposition of sticky traps with attractive
pheromone – disparlure. Only a few males of the species were trapped in all the cases.
On the other hand, rearing of the species in sleeve cages in crowns of oak trees showed that
most of inserted insects survived to adulthood, on condition that the samples were took from a
population, which was not overloaded by the slow form of infection.
These studies were repeated over a number of seasons with the ever-increasing number of the
exposed eggs, but all the attempts to establish an outbreak of Porthetria dispar failed.
Because in this ecosystem outbreaks of Porthetria dispar and other defoliators with
exception of the early-spring guild are unknown, it is the ground to state that the ecosystem stays
on the level ESPPs 3.1. “Proper control” for all the defoliators with exception of the early-spring
guild, and this level is provided by a cooperation of CESPPs 2.2.1. “Natural enemies of
invertebrate herbivores” and 2.1.1.3.1.2. "Tolerance to herbivores, Repair or compensation of
losses of host-plant tissues." This composition of EE is pertinent to the W.C. Cook’s zone (b).
As to deciduous tree species and the larch, there are a great many reports about absence of
the negative effect of defoliation in limited values on vitality of host-plants having the trait of
2.1.1.3.1.2. "Tolerance to herbivores, Repair or compensation of losses of host-plant tissues" or
even beneficial effect of it.
The studies of effect of insect defoliators on the oak in the East Europe were conducted by
A.I. Vorontsov (1967, pp. 26, 34). A weak defoliation (up to 30% of foliage) exerts the definitely
positive effect on all the vital processes in stands undisterbed by human activity, namely:
intensification of mineralization of forest litter, increase of the turnover of nutrients in ecosystem
as a whole so that the stem increment increases, and an undergrowth grows better. As to the
intermediate level of defoliation (up to 50% of foliage), losses of the increment and the dieback
take place, but in insignificant rate. Even the one-fold nearly complete defoliation does not
decrease vitality of an oak stand.
On the other hand, the complete defoliation two seasons in succession leads to partial dieback
and appearing of sprouts on oak stems that is an evidence of weakening of the trees. From the
view of ESPPs, this situation takes place of the level ESPPs 3.3. "Late control" as to the above
species of defoliators.
In the further publication, (Vorontsov, 1978, pp. 57-78) has spread the above idea as to the
effects of defoliators of diverse tree species. He has concluded that low and even intermediate
level of defoliation of trees, whose foliage might be regarded as D-II (deciduous species and the
larch) is beneficial for an ecosystem. As to the negative effect, the higher level of physiological
state of trees, the less the effect.
On the base of review of literature, P.M. Rafes (1980, pp. 87-92) explained the beneficial
effect of moderate defoliation by intensification (hyperfuction) of photosynthesis in host-plants.
In the Siberian larch, Larix sibirica at intermediate level of defoliation (30-60%), it was
recorded an increase of stem increment even in the same season (Pleshanov, 1972). The negative
effect on the larch (the dieback and tree mortality) is possible on condition that four or five-fold
heavy defoliation in succession in previously weakened trees (Prozorov et al., 1963).
The further step in understanding the essence of beneficial effect of defoliation on water
regime of host-trees. This is possible in areas of arid climate or at heavy drought in other areas.
The first report as to this phenomenon was provided by D.V. Panfilov (1972), who noticed that
the number of dying trees in next year after defoliation was greater in an Quercus robur stand,
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
where the insects had not been suppressed with insecticide treatment, comparing with a stand
without the control measures.
As an explanation of this phenomenon, it was supposed that losses of foliage due to insect
activity decreased transpiration. The effect of such defoliation is similar to that at a leaf fall-off –
the trait peculiar for many tree and brush species in the dry season growing in areas or arid
climate. The English oak, Quercus robur evolved as a species in the conditions of rather wet
climate has no such trait. When it is grown in the conditions of arid climate, defoliation occurred
to be beneficial.
This effect was substantiated experimentally by G.V. Lindeman (1993, pp. 100-101). This
scholar measured moisture of tree tissues, and found out that "potential of moisture" at the end of
May was better in trees of Quercus robur defoliated heavily by Tortrix viridana than that in the
untouched trees. The studies were conducted in 34-years old stands grown in area of very dry
climate. This was planting in the Semi-Desert biome on the border of the Volgograd and Ural’sk
Regions (Russia).
Stem borers
Stem borers (beetles of the families Ipidae, Cerambycidae, Buprestidae, Curculionidae,
insects of some genera Hymenoptera and Lepidoptera) pretend to consume vitally important
parts of woody plants –tissues of conductive concern in stems, branches, twigs, and roots
situated close to the soil surface. This is their foodstuff. The capacity of host-trees tolerate
affection by them is very limited. Therefore, all the woody plants are protected against stem
borers by traits, which are embraced by CESPPs of the categories 2.1.1.1.1.3. "Nonpreference to
herbivores, Of unknown nature" and 2.1.1.2.1.2.1. "Antibiosis to herbivores, Physiologocal
(biochemical), Permanent." These traits ensure reliable protection of host-trees on condition that
their physiological state stays on the proper level, and abundance of stem borers is not too great.
In spite of well protection of trees against stem borers, they present in noticeable numbers in any
ecosystems, where dominants have grown sufficiently to acquire the life form of woody plants.
The contradiction between the demands of stem borers and protection of their host-trees is
settled by common presence in ecosystems the biomass of the category D-III, which is suitable
for colonization by these insects. Firstly, this is the annual stem fall – a little percentage of trees
within dominants and lower stories, which die due to competition or old age. D-III embraces also
trees killed by lightning strokes, areas around of wounds on butt parts of stems or large roots,
upper parts of tree crowns affected by the dieback, broken branches and twigs. Stem borers
survive in ecosystems colonizing this stuff, but their abundance never reaches the values, at
which successful colonization of healthy host-trees is possible.
Moreover, on the level ESPPs 3.1. "Proper control", stem borers play the useful role in
ecosystems maintaining optimal structure of them, serving as a means of turnover of substances
and even as a factors decreasing danger of forest fire.
Consider these questions on an example of bark beetles, first of all the southern pine beetle,
Dendroctonus frontalis. This species is remarkable, because it has probably most developed
species potential among herbivores. It produces up to seven generations per year, and in every
generation the parent beetles are able to reemerge two-three times laying in every case several
dozens of eggs (Orr and Rodriges Lara, 1967).
It has been known numerous cases, when Dendroctonus frontalis has succeeded in realization
of its species potential establishing infestation spots with thousands colonized trees during a
season. This species demonstrates the extreme expression of the contradiction between strategy
of a herbivore species to unrestricted multiplication (in the given case in the vitally important
tree part – phloem) and the strategy of a plant to protect itself against PPs.
However, T.D. Schowalter et al. (1984) have supposed that the heavy damage due to
Dendroctonus frontalis is a result of improper human activity – establishing of pine plantations
neglecting of host-tree resistance to stem borers. In them, most part of dominants is unable to
protect themselves against the pests.
5
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Contrary, in natural pine ecosystems on vast areas of the USA, this species serves as a factor
that forming an optimal forest structure. The beetles choose in a stock of host-trees only those
ones, which begin to weaken in a result of old age, competition or stroke by lightning.
Colonizing such trees, the beetles promote a growth of near by ones by means of relief of
competition and enhancing of return of nutrients at decomposition of colonized trees.
Importantly, mineralization of the stem fall lays hindrance to accumulation of inflammable
material, so that forest fires are limited by ground cover and even useful, because they enhance
recycling of nutrients.
The role of stem borers in natural ecosystems was expressed very exactly by F.P. Keen
(1936, cited in R.C. Hawley and P. W. Stickel, 1948, p. 231) on an example of interrelations of
the western pine beetle, Dendroctonus brevicomis, and the ponderosa pine, Pinus ponderosa
Laws., namely: "Nature’s silvicultural agents which relieve the pressure of severe tree
competition or of critical growth conditions and tend to preserve a natural balance between
growing stock and available supplies of food and soil moisture."
The pine shoot moths, Evetria (Rhyacionia, Petrova) spp. inhabit terminals of young pine
trees, particularly Pinus sylvestris. These tree parts are protected by oleoresin exudation, and
healthy trees are usually free from these pests. However, at drought, terminals of pine trees, even
healthy ones, suffer due to water deficiency that decreases the protective response. This allows to
the moths to colonize them and to survive. This affection does not lead to decrease of tree
vitality, but spoils a habit of affected trees. Because the repair of shoots is possible, they might
be concerned biomass of the category D-II.
As to stem affecting phytopathogens, they are pioneers in the succession of consumers in the
process of optimizing of a stem stock structure. They infest trees at less weakening comparing
with stem borers do, they exert further destructive effect, so that such trees become susceptible to
colonization by these insects. In fact, D. L. Kulhavy et al. (1984) found out that 97% of the pines
killed by stem borers had been affected by at least one phytopathogen of the group of root rots or
the white pine blister rust, Cronartium ribicolla J. C. Fisher.
The role of stem borers and stem affecting phytopathogens may be understood better if one
consider the case of an opposite character – the situation, when these organisms are absent in an
ecosystem. Such a case was observed by the author in south Ukraine in a plantation of the
Virginian cedar, Juniperus virginiana L. This stand in the age of approximately 45 years had a
very odd structure. The trees on the forest edge had normal stem diameter (nearly 45 cm on
breast height) and well-developed crowns. However, in the direction from the forest edge to the
depth of this stand, the stem diameters became quickly very thin, and the crowns were
insignificant. The great majority of trees in this stand had a character of a long whip at the
diameter on breast height approximately five centimeters with nearly complete absence of green
needles.
The stand was planted with the aim to obtain timber for producing of pencils. The Virginian
cedar is very fit for this aim. However, such an idea was abandoned, and the stand abandoned
too, so that it appeared a unique case of destiny of a forest stand in the conditions of exclusion
of PPs.
The causes of such a structure might be explained as follows. The stand was established at a
very high stocking density. The planting was conducted with the distance between rows of the
trees 1.5- 2.5 meters and with the distance in the rows 0.5 meters. Any signs of thinning in the
stand were not seen. The activity of stem borers and stem affecting phytopathogens was absent
also. It seemed that the number of survived trees was very close to the number of the planted
seedlings.
The cause of absence of PPs in the stand seems to be the following. Juniperus virginiana is
an exotic species of the American origin. Therefore, it has no consumers in the area of planting.
In addition, the stand was established in a treeless steppe. Coniferous tree trees were not seen in
vicinity of it, so that adaptation of resident PPs to consume this species occurred to be
impossible.
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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 abnormal character of the most part of the trees suggests that they would soon die, and
only trees close to the edge would survive. Paradoxically, just the absence of PPs lays obstacles
for existing of this ecosystem in spite of the environmental conditions are quite favorable for the
species of dominants.
Thus, ecological niche of stem borers is a totality of tree parts with decreased Antibiosis
appearing now here, now there in an ecosystem. In most cases, their brood needs to leave
foodstuff, where it has developed, in the same season or in the second one, and search for new
foodstuff. This fact is important as to reflection on possibility of the "random attack" – the
hypothesis, which allows possibility of certain species of bark beetles to attack their host trees by
chance, i.e. independently to their physiological state and overwhelm their Antibiosis by means
of aggregation in a response on pheromones. On the level ESPPs 3.1. "Proper control", any
species of stem borers cannot to feed by biomass of the category D-I. They are forced to select
weakened foodstuff perceiving stimuli of primary attraction producing by weakened parts of
host-trees.
Contrary, in the conditions of a bark beetle outbreak, i.e. when an ecosystem lowers on the
level ESPPs 3.3. "Late control," concentration of pheromones of aggregation in air becomes
high, and aggressive species of bark beetles probably perceive this stimulus as a possibility to
attack host-trees indiscriminately.
It should note that within stem borers, there exists the wide range as to necessity to take into
account physiological state of host-trees at attacks of them. The aggressive species on condition
that an amount of their population is large, are able to ignore the state of the trees. Other species
are forced to perceive stimuli of primary attraction very sensitively, because the only accessible
objects for colonization by them are small portions with deteriorated tissues within healthy trees.
Such species are common in arid areas and in the habitats with contrasting water supply (the
flood plains). In such conditions, temporary water deficiency is common and severe. Woody
vegetation responds on the deficiency by a drying up of some portions of twigs, branches or
exposed sites on a stem. After returns of favorable weather situation, their vitality might be
restored. But in the period of deficiency of watering, these parts can be attacked successfully by
stem borers. Their brood developed here to adulthood. The trees with such affected plots can live
a number of decades sometimes cicatrizing of borer’s wounds.
Many data about such species have been offered by G.V. Lindeman (1993). There are the
grounds to suggest a specific way in coevolution of interrelations between stem borers and their
host-trees. The life strategy of such stem borers consists in an infliction of minimal damage to
host-trees. They do not intend to girdle the stems and direct their galleries into a hardwood
portion of a stem, so that vitality of host-trees is not decreased. Prolonged continuing of vitality
of the trees with colonized parts is necessary for existence of the stem borers, because quick
dying of the trees would lead to mortality of the brood due to desiccation. Moreover, these
species of the borers are characteristic for areas with limited resource of host-trees. The mortality
of them at colonization as it takes place in the aggressive species of stem borers would result in
quick exhaust of the resource and in extinction of these species of stem borers.
Notably, the developing of the stem borers on small plots of stem is beneficial for such trees.
This is so because the colonies of stem borers are usually mortised by woodpeckers. The hollows
appeared in a result of woodpecker’s predation, are used for nesting by diverse species
insectivorous birds. In a result, a tree obtains a ptotection from defoliators and a source of
fertilization in term of excrements of these birds. Such interrelations might be defined as semisymbiotic. They are flourish on the level ESPPs of the level 3.1. "Proper control. "
This group of stem borers includes a number of the engraver bark beetles of the genus
Scolytus, in particular S. kirschi Scal., and S. zaitzevi But. on the species of the elm, Ulmus
spp. in arid areas, the longhorned beetles Cerambyx cerdo L. on the oak, C. dux Fald. on the fruit
trees, several species of the clear-winged moths of the families Aegeriidae – Aegeria (Sesia)
spp., and Paranthrene spp .on the poplar, the birch and fruit species, the leopard moth, Zeuzera
pyrina L. on the ash, the goat moths, Cossus cossus L. and C. terebra F. on various deciduous
7
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
species, the large poplar longhorned beetle, Saperda carcharius L., the small poplar longhorned
beetle, Saperda populnea L. on the poplars.
The same traits have the European spruce beetle, Dendroctonus micans, and the black
turpentine beetle, Dendroctonus terebrance. The primary ecological niche of D. micans is an
area around wounds in butts of spruce stems inflicted, in particular by the bear. Such an affection
is usually tolerable for vitality of the host-trees, so that the level ESPPs 3.1. "Proper control" is
not disturbed.
Thus, the level ESPPs 3.1. "Proper control" is a state of ecosystems, at which they are able to
keep continually all the PPs as the components useful for prosperity of all the community.
Sap-sucking arthropods
Unlikely to defoliators and stem borers, sap-sucking arthropods (aphids, coccids, and mites)
are common on diverse parts of trees independently on physiological state of host-trees. This is
so because these organisms are able to evade from antibiotic protective means of their hostplants at least at Low density. The Low density is kept by their natural enemies. This is tolerable
for host-trees, because a negative effect of the sap-sucking arthropods is much less than that of
defoliators. When the damage exceeds of the threshold, the secondary Antibiosis (CESPPs of the
category 2.5.1.) enters into operation.
The characteristic of aphid’s density as Low one is the following: this is a density, at which
the negative effect on host-plants does not observed. In doing, the number of aphids per not too
large tree can reach million insects (Owen, 1977).
Therefore, as to sap-sucking arthropods, all the plant parts serve as biomass of the category
D-II. When thier density is Insignificant or Low, this is the level ESPPs 3.1. "Proper control." In
the case, when the threshold is exceeded Low level, ecosystems enters to ESPPs 3.2. "Lag
control" or 3.3. "Late control."
Sap-sucking arthropods are numerous herbivores in the ecosystems especially with deciduous
tree species as dominants on the level ESPPs 3.1. "Proper control." Due to well-developed
tolerance of host-trees, these insects feed not only on foliage, but also on twigs and stems
without any negative effect of tree vitality. The effect of their feeding is useful. Thus, D. Owen
(1977) reported that a not too large tree of the lime, Tilia sp. 14 meters in height bore usually
nearly a million of aphids having no signs of depression. In the same time, these aphids feed up
their host-trees. This process is following: the honeydew that is produced by the aphids is
washed away by rains, and it gets into the soil. Here hydrocarbons containing in the honeydew
stimulate vital activity of microorganisms fixating air nitrogen.
D. Owen (Ibid.) reported that the stimulation due to entering glucose into the soil increases
abundance of the microorganisms of the genus Azotobacter in one thousand times.
Vertebrate herbivores
The studies in steppe reserves have shown that at the normal rate of precipitation, vertebrates
consume 10-20% of production of dominants, whereas at drought the consumption grows up to
38% (Abaturov and Kuznetsov, 1973). Further, B.D. Abaturov (1979) supposes that such a value
of the consumption is abnormally low, and it is caused by human effect (the disappearing of
hoofed animals), so that only rodents consume steppe vegetation. When human interference is
absent, that takes place in African savanna reserves, the normal rate of consumption of biomass
reaches 70% of the annual production. Because destructive effect of them is unnoticeable, this
situation should be considered as the level ESPPs 3.1. "Proper control." This is possible, because
dominants in these ecosystems are protected by CESPPs of the category 2.1.1.3.1. "Tolerance to
herbivores." It operates in a cooperation with CESPPs 2.2.2. "Natural enemies of vertebrate
herbivores" and CESPPs 2.4. "Periodic (bottle-neck) suppression."
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Such a rate of the consumption is considered by the above scholars and many others as
necessary one for maintenance of optimal species composition and structure of a stem stock in
grassy ecosystems.
The level ESPPs 3.2. Lag control
Ecosystems occur on the level ESPPs 3.2. "Lag control", when outbreaks of herbivores,
which have arisen in them, are declined, when density of herbivores has not reached High level.
The exeption concerned the early-spring guild of oak defoliators will be considered below. The
decrease of level ESPPs from 3.1. to 3.2. takes place under the stressors, which suppressed
activity of CESPPs of the Extrinsic class. The restoration of the level ESPPs 3.1. proceeds in a
result of cessation of impacts due to a stressor at resurgence of activity of CESPPs of the
Extrinsic class. Thus, on the level 3.2.”Lag control”, CESPPs of the category of the Intrinsic
class 2.5. “Effects of crowding” do not enter into operation.
Defoliators of evergreen coniferous tree species
Droughty weather is a common releaser of outbreaks of defoliators in stands of Pinus
silvestris. This fact is explained as a result of decrease of oleoresin exudation in pine needles, i.e.
of CESPPs 2.1.1.2.1.2.1. “Antibiosis to herbivores, Physiological (biochemical), Permanent”
does not operate. An onset of a wet weather situation induces a decline of such outbreaks.
Here is an example of such events for Dendrolimus pini. At onset of heavy rains in July or
August, young larvae of this species disappear. The cause of it consists in mortality of the larvae
due to increased oleoresin exudation in pine needles in the conditions of abundant watering (V.I.
Grimal’s’ky, pers. comm.). Drops of oleoresin kill the young larvae. Because ESPPs is restored
by a chance, this is a situation of the level 3.2. "Lag control" on the biomass of the category D-I
– needles of evergreen coniferous species.
Again, H. Klomp (1966, pp. 271, 286) reported that mortality of first instar larvae of the pine
looper, Bupalus piniarius "…appears thus to be a predominant component in the determination
of the pattern of density fluctuation…In general, we are inclined to attribute most of the
fluctuations to the effect of weather…" and "This mortality rate is computed as a difference
between July and August densities..."
This situation might be considered as a case of ESPPs 3.2."Lag control", when progressing
of an outbreak is interrupted by onset of the weather situation, at which protective response of
host-plants restores.
Defoliators of deciduous tree species
The level ESPPs 3.2. “Lag control” is characterized by increase of density of the defoliators
to the value Intermediate in the spring-summer, summer-fall, and fall-spring guilds. Contrary, in
the early-spring guild, the increase is common to the level High.
As to the early-spring guild, ecosystems occur on the level 3.2. “Lag control”, when it
decreased an operation of CESPPs 2.1.2.1.1. “Superevasion from hervivores” cooperating
closely with 2.3.14.2. “Mortality due to enhancing of host-plant evasion as to the early-spring
guild.” As to the rest of the guilds, this level ESPPs takes place at decrease of an operation of
CESPPs 2.2.1. “Natural enemies of invertebrate herbivores.”
The exertion of negative effect to host-trees at consumption of foliage of deciduous trees is
uneven within diversity of guilds of defoliators. The early-spring guild is a category of
defoliators, whose negative effect on dominants is much less comparing with that in other guilds
of defoliators. Even High density of them, if it stays no more than one season, is negligible for
vitality of dominants. They are able to tolerate it. High density of the early-spring guild is
common in the ecosystems, where density of the spring-summer guild stays continually on the
level Insignificant, i.e. this is ESPPs 3.1. "Proper control" as to the summer-spring guild.
9
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 difference between the early-spring and spring-summer guilds of oak defoliators as to
exert damage to host-trees at the same value of defoliation was shown by A.I. Vorontsov et al.
(1991). In the former, one-fold 90% defoliation did not cause mortality of affected trees (Ibid., p.
211), whereas in the latter, such a defoliation resulted in 3% mortality of the trees (Ibid., p. 212).
Because in the above case 90% defoliation by the early-spring guild did not cause a
noticeable negative effect on its host-trees, this situation should be considered just as the level
ESPPs 3.2. “Lag control” despite of density of defoliators reached the value “High.”
There are the data, which demonstrate CESPPs, which enter into operation of the level ESPPs
3.2. "Lag control" on biomass of the category D-II, so that the level ESPPs 3.1. “Proper control”
restores.
Not too large infestation spots of defoliators are destroyed sometimes by wandering flocks of
the birds. A.G. Kotenko (1977) observed that infestation spots of Porthetria dispar of a limited
area in south of Ukraine are suppressed by flocks of the cuckoo, Cuculus canorus L.
This predation is a response on increased density of a prey, although delayed comparing with
the level ESPPs 3.1. "Proper control", when the birds do not allow an increase the density to such
values. There are no evidences of operation of CESPPs of the category 2.5. "Effects of
crowding." This suppression takes place by a chance, so that they might be concerned as the
cases of the level ESPPs 3.2. "Lag control."
Further, in the same area, A.G. Kotenko (pers. comm.) observed suppression of little
infestation spots of the same species by parasites. In the context of the present discourse, it is
important that it takes place at the Intermediate level of density of the insect host, and these
parasites penetrate from outside, i.e. by a chance.
The events in the given case are the following. These infestation spots arise in oak groves
having areas up to several hectares. Treeless areas in hundreds of meters separate the groves. A
frequency of arising of the infestation spots is high – every several years, but they are shorttimed, and the defoliation does not exceed 70%. An arising of the infestation spots is caused by
extinction of hymenopterous parasites, because in the small groves with low species diversity
they do not have a possibility to find alternative hosts. In addition, the treeless distance among
the forest plots lays obstacle to find favorable conditions in a near by forest. This is so because
these tiny insects are very sensitive to high air temperatures and low humidity. When the
parasites extinct in a given grow, it takes place increase of Porthetria dispar density, rather that
this species spreads on large distance easily. As soon as the parasites have had success to
overcome the distance among the groves, they quickly reproduce and suppress of a population
their insect host, because the parasites have higher reproductive potential – a number generations
per season and polyembria.
Thus, the suppression of Porthetria dispar proceeds by a chance. It depends on weather
situation, including air temperature and moisture, direction of the wind, the distance among the
groves, their species composition and structure.
The common cause of suppression of a Porthetria dispar population is an onset of weather
situation, which provides an 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."
In this context, it should cite R.W. Campbell (1973) "…heavy precipitation in June…, if
sufficiently spread, may indicate the abrupt collapse of the outbreaks phase.. " If it takes place on
the outbreak phase, this is the level ESPPs 3.3. "Late control." The same CESPPs is able to
operate on the level 3.2. "Lag control." This gets clear if to recall the situation in the W.C.
Cook’s zone (с). Such a weather situation occurs in this zone nearly every year. It suppresses the
resident population of Porthetria dispar in the beginning of a growth of its density.
In the Moscow Region (Russia), which is situated in this zone in beginning of 1950-ies and
in 1980-ies, it was recorded increases of density of the resident population of this species, which,
however, were not developed in true outbreaks. Probably, those were the cases of restoring of
ESPPs 3.1. “Proper control” under effect of CESPPs 2.3.3. "Cool and prolonged rains in the
10
G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
larval stage of defoliators" with the effect 2.3.3.1. "Mortality of larvae at inducing of the acute
form of infection" entering into operation on the level ESPPs 3.2."Lag control."
Fluctuations of density of the early-spring guild of oak defoliators are determined by weather
situation, which effect on coincidence of larval hatching and bud-bursting in host-trees. It is
easily to determine the level ESPPs 3.3. “Late control”, where High density stays several years
in succession. But it is difficult to discriminate the levels 3.1. “Proper control” and 3.2. “Lag
control”, because the fluctuations of the density has unpredictable character from Low to High.
In addition, the density nearly always does not decrease lower than “Low” over all the range of
the oak. Therefore, there are the grounds to suppose that the level ESPPs 3.1. “Proper control” as
to this guild is not known validly, the consideration is limited by the levels ESPPs 3.2. "Lag
control" and 3.3. "Late control."
The level ESPPs 3.2. as to Zeiraphera diniana. on the larch, Larix spp. is known badly.
Stem borers
The case described by A.A. Berryman and M. Ashraf (1970) might be considered as the level
ESPPs 3.2. "Lag control" concerning stem borers. In so doing, the engraver bark beetle, Scolytus
ventralis Lec. attacked standing trees of the grand fir, Abies grandis Dahg. weakened by drought.
Until the drought continued, development of beetle’s brood on these trees proceeded without
hindrance. After finishing of the drought, physiological state of the attacked trees became better,
and they exerted a protective response. A destiny of the brood occurred to be dependent on
density of the attacks. On the trees, where attack density was more than 0.3 pieces per square
decimeter of the stem surface, the brood survived to adulthood, and the trees died. At such attack
density, the trees were weakened by the beetles too much so that their vitality could not be
restored. At attack density below of the above-mentioned threshold, the brood died, whereas the
trees survived. The overall number of the died trees equaled 5% of those being under the
observation.
The level ESPPs 3.3. Late control
The level ESPPs 3.3. "Late control" is a state of ecosystems, where decrease of ESPPs has
advanced so far that resurgence of activity of CESPPs of the Extrinsic class gets impossible. The
restoration of the level of ESPPs 3.1. “Proper control” takes place due to operation of CESPPs of
Extrinsic class 2.5. “Effects of crowding.” Consider proceeding of this process in diverse groups
of herbivores.
The defoliators of evergreen coniferous tree species
The peculiarities of the level ESPPs 3.3. "Late control" in this group of defoliators get clear if
to consider the situation in ecosystems of Pinus silvestris in East Europe. This level of ESPPs is
unknown in primary pine forests – the last rest of biocenoses with this species as a dominant.
Contrary, the level ESPPs 3.3. "Late control" is common in pine articenoses, which were
established on vast areas over XX century. They are overstocked even-aged monocultures,
unthinned, because these measures are unthrifty in young forest stands. Often, they grow in the
conditions of the shallow effective depth of the soil, in particular on old field areas. Beginning
with the stage of thicket (approximately 15 - 40 years), when competition among the trees is
particularly intensive, in them, it is common infestation spots of pest insects and epiphytoties of
phytopathogens. Nearly every year, rate of oleoresin exudation in their needles is low that allows
to defoliators to thrive. Therefore, density of them is determined by intrapopulation regularities
of the defoliators, and frequency of outbreaks of such species as the pine sawflies is close to ten
years. The resurgence of ESPPs to the level 3.1. is provided by CESPPs 2.5. "Effects of
crowding" entering into operation, when the density becomes High, i.e. the defoliation is nearly
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
complete. When insecticide treatments in such affected stands are not applied, it is common
partial mortality of the main stock of dominants at outbreaks of the pine sawflies, or overall
mortality at outbreaks of Dendrolimus pini.
Pine ecosystems on the level ESPPs 3.1. "Proper control" can be lowered on the level ESPPs
3.3."Late control" at mass immigrations of late-instar larvae, which leave stands with overall
defoliation in search for food. Such events are known in Dendrolimus pini, D. sibiricus, and
Porthetria dispar. The latter species produces primary outbreaks in ecosystems of deciduous tree
species, but starving late-instar larvae are able to crawl outside and to feed successfully without
distinction by evergreen coniferous species.
The defoliators of deciduous tree species.
Consider the peculiarities of the spring-summer guild of the defoliators of deciduous tree
species. As a model species, it serves Porthetria dispar. As to it, the ecosystems of the level
ESPPs 3.3. "Late control" are common in the Forest-Steppe biome in East Europe, especially in
its southeastern part, and in near by areas of West Siberia. The oak, the birch, the aspen and the
lime are dominants in them. These ecosystems are characterized by disturbing structure of the
stand and poor species composition comparing with those in ecosystems of the level ESPPs
3.1."Proper control." Most of these ecosystems are of natural origin in the past, but they are very
changed in further human management. Firstly, they have a low stocking density. This is a result
of the coppice origin of present stock in the oak ecosystems as dominants. They have been
undergone of numerous cutting, so that in the trees of present stands, the oak dominants are
deprived of the main (pivot) root, which dies off at cutting of a tree. This loss results in poor
providing of the affected trees with moisture from the soil. Therefore, many trees die, and
stocking density becomes low, and the tree crowns become rarified. Further, an undergrowth is
nearly absent, and grass cover is suppressed by livestock. These changes open onset on
temperature extremes into the ecosystems that produce hostile environment to tiny species of
defoliators’ parasites – drought in spring and summer, and severe frost in winter.
In the conditions of arid climate, as that in West Siberia, even dominants of natural origin
(the birch and the aspen) are grown sparsely. In addition, these stands are used for grazing over
centuries. There, the suppression of grass cover and brush undergrowth is nearly complete, so
that, parasites of the defoliators do not have protection from hostile environment. Also, they do
not have flowering plants for imaginal feeding and points of mating. The insectivorous birds
suffer due to a lack of sites for nesting. These ecosystems are so changed comparing with
primary forest that they might be considered as articenoses.
In the conditions of arid climate, where CESPPs 2.3. "Routine weather suppression" is weak,
the above circumstances constitute optimum for the defoliators, which reach the outbreak phase
nearly every ten years. This is the W.C. Cook’s zone (a).
In the climate of more abundant precipitation – the W.C. Cook’s zone (b), the intervals
between the outbreaks in longer, especially on the northwest border on the zone (b), where they
reach 18 years.
The decline of these outbreaks takes place only in the conditions, when density of the
defoliators reaches the value High. Nevertheless, longevity of the period of High density depends
on climate of the area. It is more prolonged in the W.C. Cook’s zone (a) than that in the zone (b).
The difference is explained by the unequal possibilities of upraise of activity of natural enemies.
In the zone (b), an onset of the wet weather situation, which promotes activity of parasites, avian
predators and pathogens in the acute form of infection, is common, that induces the decline of
outbreaks under effect all the complex of natural enemies. This is an operation of CESPPs of the
diverse subcategories of 2.5. "Effects of crowding." The main are 2.5.2. "Attraction of predators
and parasites", 2.5.2.1. "Mortality under effect of predators and parasites", 2.5.3. "Increase
activity of pathogens and parasites in the specific conditions of high host density", 2.5.3.1.4.
"Mass mortality due to affection by acute form of infection and parasitization."
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
Contrary, in the zone (a), weather situation often continues to be hostile for resurgence of
activity of parasites, avian predators, and the acute form of infection in pathogens. In the zone
(a), it is important activity of the effect 2.5.3.1.5. "Spontaneous or winter mortality of embryos"
and 2.5.4. with the effect 2.5.4.1. "Suppression of defoliators over the period, which provides a
reprieve for restoring of vitality of dominants." The latter operate also in the zone (b), but its role
in this zone is less.
The same regularities are peculiar for the defoliators of deciduous tree species of the
summer-fall and fall-spring guilds.
The level ESPPs 3.3. "Late control" in the defoliators of the early-spring guilds also takes
place in ecosystems with suppressed activity of natural enemies. As a model of this guild, it
serves the oak green moth, Tortrix viridana. In addition, in these ecosystems, it takes place a
lack of operation of CESPPs of the category 2.1.2.1.1. "Superevasion from herbivores,"
2.1.2.1.1.2. "Exposition to 2.2.1." This is a result of presence in the ecosystems of phenological
forms of the oak with diverse terms of bud-bursting, so that the neonate larvae are able to find
their foodstuff every year. In such conditions, density of the guild stays on the High level during
the period more than a season. The decline comes abruptly at severe winter. In this case, it
operates CESPPs 2.5.3. with the effect 2.5.3.1.5. "Spontaneous or winter mortality of embryos."
The winter moth, Operophthera brumata reaches High density very often in the conditions of
flood plains, where flooding kill entomophagous organisms inhabiting forest litter. The oak
ecosystems on such conditions are on the level ESPPs 3.3. "Late control."
On the level ESPPs 3.3., damage on the part of oak defoliators is significant. In fact, A.I.
Vorontsov et al. (1991) reported that at complete defoliation by the spring-summer guild of
defoliators over three seasons in succession, mortality of affected trees equaled 50% (Ibid., p.
212). At the same defoliation by the early-spring guild, the mortality reached 15%, and at fourfold defoliation by this guild – 43% (Ibid., p. 211).
It should note that such heavy and continual defoliation is pertinent to oak ecosystems, which
are very disturbed by people, where physiological state of trees is improper. Therefore, the high
values of tree mortality are probably are due to preceding weakened state of trees in a
cooperation with negative effect of the defoliation.
As to the zones (с) and (d), the level ESPPs 3.3. "Late control" as to the spring-summer guild
is impossible there at once. This is so because climate of these areas lays obstacles for growth of
density of this guild the to theHigh level.
The stem borers
Because their ecological niche is conductive tissues of trees having no Antibiosis, the level
ESPPs 3.3. "Late control" for them takes place, when physiological state of numerous trees
within the main stock of dominants becomes weakened. In such trees, both Antibiosis (CESPPs
2.1.1.2.1.2.) and Nonpreference (CESPPs 2.1.1.1.1.3.) are decreased. The foodstuff resource of
stem borers, which before the effects of a stressor were forced to limit themselves by D-III,
occurs much greater. Therefore, the amount of resident populations of stem borers becomes
greater - sufficient to colonize a significant part of the main stock of dominants, even if they
weakened not too much.
The processes connected with the density have been studied well in the bark beetles. By
means of developed pheromonal communication, the bark beetles are able to regulate density of
their colonies depending on availability of the resource. The advantage of Low density of
colonies consists in providing of the brood by abundant food (phloem of host-trees), so that the
"production" – the ratio of adults in the brood to the parent beetles becomes maximal of the
possible. When developing in conditions of Low density, the every insect of the brood is
separated from others by undisturbed phloem. Therefore, the brood is inaccessible for predation
on the part of subcortial satellites of the bark beetles.
Further, the woodpeckers, which consume significant part of the brood in D-III on the level
ESPPs 3.1."Proper control", become less effective predators on the level 3.3. "Late control." This
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
is so because the birds need to exert much more efforts for hunting the sparse insects, which stay
often in hardly accessible sites, on windthrown trees for example. At last, the brood developed in
the conditions of well nourishment has good physiological state, and, therefore, is able to
withstand diverse abiotic stressors. Therefore, an amount of a resident population of stem borers
grows until weakened foodstuff will be exhausted.
The species of low aggressiveness are forced to thicken the number of attacks on the rest of
weakened trees, whereas the aggressive species are able attack healthy host-trees. Possessing by
pheromones of aggregation, they are able to perform mass attack and colonize even healthy
trees. However, their populations need to pay a heavy tribute for this success. This is so because
the mass attacks results in High density of the colonies, that in turn puts into operation diverse
CESPPs of the category 2.5. "Effects of crowding." The production decreases up to zero, and
brood becomes weakened. The populations undergo a decline. Such is a nature of ESPPs of the
level 3.3. "Late control" in the bark beetles. In aggressive species of them, such a restoration of
ESPPs of the level 3.1. “Proper control” is accompanied by significant mortality of the main
stock of dominants.
The capacity of the aggressive species of bark beetles to overcome self-protection of hosttrees results in a specific situation of the lowering of the level ESPPs 3.1."Proper control" to the
level 3.3. "Late control" by means of mass immigration of the beetle from heavy affected
ecosystems. In such a situation, it takes place the mass attack on main stock of dominants,
colonization of part of them and effects of CESPPs 2.5. "Effects of crowding" in the brood.
The same is true for aggressive species of stem borers of other families. Thus, at large
amount of populations, the long-horned beetle, Monochamus urussovi Fisch. is able to prepare
its healthy host-trees for development of the brood by means of weakening of the trees at
imaginal feeding on twigs outside of ecosystems with initial outbreaks (Isaev et al., 1983).
Nevertheless, this success needs to be paid by heavy mortality of the pest at the colonization, so
that its density decreases to Low value.
Sap-sucking arthropods
An example of the level ESPPs 3.3. "Late control" in the sap-sucking arthropods is presented
by the case of the invaded species Adelges (Dreyfusia) picea Ratz. affecting the fir Abies alba
Mill. in Europe (Franz, 1956; Karafiat, Franz, 1956; Kloft, 1957). Having no effective natural
enemies among resident species, this species reach High density that is not characteristic for
native species of this group. The affection provokes a protective response of host-trees. In so
doing, in phloem, where the aphids direct their stylets, it appears a layer of cells, which impede
feeding of the insects. They disappear from the trees. Further, the response is accompanied by
forming of a cambium layer, which allows continuing the normal growth of stem tissues, so that
the negative effect of the pest is neutralized. This response might be considered as entering into
operation CESPPs 2.5. "Effects of crowding", with the effects of 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 secondary protective barriers in
affected tissues" with the final effect 2.5.1.2.1.1. "Starvation."
ARTICENOSES
The progress of mankind is characterized by steadfast expansion of articenoses. All the fields
of agricultural crops, all the fruit orchards, most part of forest stands in Europe, many pastures
belong to ecosystems of this category. They need in protected against PPs by CESPPs of the
Antropic class of category 2.6. "Human control measures."
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.6.1.1. Growing of cultivars resistant to plant pests.
When establishing of articenoses with the plants as dominants having the traits of resistance
to PPs in their heredity and applying cultural practices, which provide these plants with vital
resources – nutrients and moisture, the level ESPPs A.3.1. "Proper control" is achieved nearly
exclusively by CESPPs 2.6.1. "Promotion to ecosystem stability by means of exploiting of the
CESPPs of categories 2.1., 2.2., 2.3., 2.4. per se or with modifications." In so doing, a need in
application of CESPPs 2.6.3. "Temporary suppressive measures" is usually absent.
2.6.1.1.1. Growing of taxa with natural trait of CESPPs 2.1.
The practice of forestry is rich by examples of usage of this category. Consider the case of
successful application of this method. In south of Ukraine, in the Lower-Dnieper area, there
exists the terrain of the sandy soils expand on thousands of hectares. The soils arose several
centuries ago in a result of degradation of dry steppe ecosystems due to overgrazing. These bare
sands are unfit for agriculture, and bear danger for surrounding areas due to further expansion of
the sands at moved them by the wind.
For melioration of this area, it is used afforestation, and as dominants in the establishing
stands, a number species of the pines have been tested as tree species most suitable for growing
in conditions of arid climate on the sandy soils. Two pine species - Pinus sylvestris L. and
P. pallasiana Pall. occurred to be perspective for the afforestation.
The species composition of the plantations of these pine species is diverse. They are pure or
mixed of both species. By studies by D.F. Rudnev and N.E. Kononova (1964), D.F. Rudnev and
V.P. Smelyanets (1968), M.M. Padiy (1969), it was shown that in any stands, trees of P.
sylvestris are affected heavily by the pine shoot moths, Evetria (Rhyacionia, Petrova) spp.
Contrary, trees of P. pallasiana in any cases are nearly free from these insects. Although the
moths lay their eggs on buds of this species, but neonate larvae are unable to penetrate into thick
cover of its buds or die under effect of abundant oleoresin flow (Padiy, 1969). Therefore, in this
case, it is exploiting the CESPPs 2.1.1.2.1.2.1. "Antibiosis to herbivores, Physiological
(biochemical), Permanent." Notably, that the lack CESPPs 2.1.1.1.1. "Nonpreference to
herbivores" on P. pallasiana serves for trapping of the pests, protecting in some degree the
susceptible species – P. sylvestris.
Being widely spaced at planting, P. pallasiana trees are able to regenerate in such conditions,
and the young trees are free of affection by the PPs, so that these articenoses demonstate traits of
biocenoses.
2.6.1.1.2. Growing of cultivars with bred trait of CESPPs A.2.1.
In agriculture, "Growing of resistant varieties is regarded by many to be the ideal way to
control many crop pests" (Knipling, 1979, p. 555). The resistance might be achieved by a
number of ways with usage of diverse categories of CESPPs A.2.1."Plant resistance to PPs."
The good example is the case of Mayetiola destructor in Kanzas. R.W. Painter (1958, p. 277)
reported that over a number of years "under combination of unfavourable weather and resistant
varieties…" this species "…has decreased to the point where it has been almost impossible to
find any evidence of the insect…" This case demonstrates the usage of CESPPs A.2.1.1.2.1.
"Antibiosis to herbivores" and 2.3. "Routine weather suppression."
Another way of maintenance of ESPPs on the level A. 3.1. "Proper control" to this species,
and other species of cereal flies has been used by breeders in Ukraine (Vasechko, 2001). There,
as the protective traits, it operates high capacity to general tillering, to compensate losses of
tillers, to develop in the period of fall, when activity of the cereal flies is low and to do the same
in spring, when density the flies is decreased after overwintering. The latter trait allows to the
plants to finish their vulnerable stages before an increase of flies’ activity. These traits occurred
to be a reliable measure of protection of the winter wheat against the flies in the conditions of the
Forest-Steppe biome, where activity of the flies is not too high.
In the above example, it is used CESPPs A.2.1.1.3.1.2 "Tolerance to herbivores, Repair of
compensation of losses of host-plant tissues" and CESPPs A.2.1.2.1.1. "Superevasion from
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
herbivores" in cooperation with CESPPs 2.4. "Periodic (bottle-neck) suppression." These
CESPPs occurred to be effective for protection of the winter wheat against a number of groups
of other arthropod pests – sap-sucking ones and defoliators.
Importantly, in this area, an amount of pests’ populations is not too much that might be
explained by the effect of climatic conditions, i.e. CESPPs 2.3. "Routine weather suppression"
and CESPPs 2.2.1. "Natural enemies of invertebrate herbivores", so that these CESPPs serve as
cooperators of CESPPs A. 2.1. "Plant resistance to PPs."
As to the stem sawfly, Cephus pygmaeus, thickness of stem tissues serves as a means of selfprotection in the winter wheat. (Shapiro et al., 1990). This is an operation of CESPPs
A.2.1.1.2.1.1.1. "Antibiosis to herbivores, Structural, Permanent."
The diverse ways of maintenance of ESPPs to Leptinotarsa decemlineata is used by breeders
of the potato. In USSR, it was bred varieties of the potato with high content in foliage
glicoalcaloids, which provided the varieties with Antibiosis to the insect. One of the varieties
(Zarevo) was recommended for agriculture. This is a case of usage of CESPPs A.2.1.1.2.1.2.1.
"Antibiosis to herbivores, Physiological (biochemical), Permanent." To the point, this variety has
not obtained popularity, because the content of protective substance in it is dangerous for feeding
by people.
Also, it is grown early ripening varieties of the potato, which have time to produce the yield
before the emergence of second generation of the beetle, when its population is very numerous.
Such varieties need in a single treatment with insecticides in early spring, when the beetles
establish the first generation. This is the case of exploiting of CESPPs A.2.1.2.1.1.
"Superevasion from herbivores" and CESPPs A.2.1.1.3.1. "Tolerance to herbivores" in a
cooperation with 2.6.3.3. “Temporary suppressive measures sensu stricta.”
Antibiosis (A.2.1.1.2.2.) and Tolerance (A.2.1.1.3.2.) were used at breeding of potato
varieties resistant to the phytophthorosis, Phytophthora infestance (Mont.) De Bary. The latter
trait occurred to be even more prospective than the former. In fact, two varieties with Tolerance
(Lugovsky and Volovetsky) produced the yield of tubers 10 metric tons per hectare, whereas five
varieties with Antibiosis – 7 metric tons.
The above potato varieties were bred in the Ukrainian Potato Institute, Kyiv (Nemeshayevo).
2.6.1.2. The usage of cultural practices, which maintain the resistance by keeping healthy
state of plants
The usage of resistant to PPs cultivars, both wild species and varieties, needs in a providing
of them with the conditions of growth, which necessary for keeping of proper physiological state
of plants. Turning to the above case of successful growth of Pinus pallasiana in the LowerDnieper area, it should note that it grows well on condition that proper silvicultural practices are
applyed. They include wide spacing of seedling at planting, and usage as an admixture of
nitrogen-fixing species, particularly the black locust, Robinia pseudoacacia. Contrary, at
establishing of the plantations with dense spacing (10,000 pine seedling or even more per ha)
and pure species composition, as it has been adopted in last decades, the resistance to PPs is not
maintained.
It is known that pine monocultures on old-field lands are suffered due to outbreaks of pest
insects and epiphytoties of phytopathogens, especially beginning with the stage age of thicket
(approximately after 15 years), when the trees begin to compete intensively for soil resources.
Nevertheless, it is possible to grow stable monocultures of Pinus sylvestris on old-field areas if
to practice proper soil treatment, healthy seedlings, and wide spacing of the trees. Such
plantations were free of serious damage by PPs at least over several decades, when observations
were conducted (V.I. Grimal’s’ky, pers. comm.). In so doing, a need in CESPPs 2.6.3.3.
"Temporary suppressive measures sensu stricta" is minimal. The only measure of this kind is
applying of insecticides for protection of the seedling at planting against grubs of the cockchafer,
Melolontha spp. in the periods of High density of these insects. At such practices, people use
CESPPs 2.1.1.2.1. "Antibiosis to herbivores" and 2.1.1.3.2. "Antibiosis to phytopathogens."
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
All the complex cultural practices in agriculture aimed on obtaining high yield and the best
quality of production should be considered as effect of CESPPs 2.6.1.2. Indeed, these aims
cannot be achieved if crops do not have proper physiological state. This is a prerequisite for
operation of all the CESPPs 2.1. "Plant resistance to PPs."
2.6.1.3. Introducing of natural enemies of herbivores
This is an establishing of the complex of natural enemies in the environment, where a
herbivore species is free from them. This province of measures concerns importation of natural
enemies with the aim to suppress an invaded (exotic) species, which occurred to be a pest. In
such practice, it is used CESPPs A.2.2.1. "Natural enemies of invertebrate herbivores." This
human activity is well represented in literature.
From the numerous cases of successful importation of the natural enemies, it will be chosen
for further consideration in the Section 6(1) the lady beetle, Rodolia cardinali Mulsant in
California. This predator is notable by its uncommon effectiveness that result in some orchards
to disappearing of its prey – the coccid, Iceria purchasi Maskel. Therefore, it is interesting to
discuss the issue, why the predator does not exhaust its food resource and survives.
2.6.1.4. Promotion to native natural enemies of herbivores
This is the usage of cultural practices, which allow resident natural enemies to suppress pest
species of herbivores.
Forestry provides good examples of efficacy of cultural practices in protection articenoses
against pest insects. The successful case of protection of an articenosis against Porthetria dispar
established in severe environmental conditions was observed by the author in southern steppe in
Ukraine, the Donetsk Region. This was the stand with Quercus robur as dominants in the age
approximately 100 years. The stocking density of this stand was low that it was necessary for
providing of the trees by moisture in arid climate. The undergrowth consisted of diverse species
of brushes, and was very thick that obviously allowed natural enemies of defoliators to thrive.
According to a report of local silviculturists, in this stand, density of Porthetria dispar
sometimes increased. However, a growth of the density was interrupted before it reached
significant defoliation, so that treatment by insecticides was not needed. Also, there were no
problems with other species of defoliators.
In agriculture, even small reserves of wild vegetation exert surprisingly beneficial effect on
activity of natural enemies of pest insects. Above it was quoted report of R.L. Doutt and
R.S. Smith (1969) about suppression of the grape leafhopper, Erythroneura elegantura Osborn
by its parasite Anagrus epos Girault., when within two miles around a vine-yard, plots of the
blackberry were grown. In them, the parasite survived.
Ch. S. Elton (1958. Ch. IX) convincingly agitated for maintenance of plant hedges and
shelterbelts, which served as reservations of diverse species of animals including natural enemies
of agricultural pests.
G.A. Viktorov (1967, p. 247) considering causes of chronic damage in cereal crops by the
sunn bug, Eurygaster integriceps Put. concluded that the damage is a result of suppression of its
natural enemies in the conditions of intensive agriculture. Here, biocenoses were changed by
articenoses, where the natural enemies cannot find additional insect hosts and sites for
hibernation. To promote the natural enemies, it was recommended to maintain shelterbelts and
grow perennial grasses.
The role of reservations for parasites might be seen from the data on affection of eggs of the
sunn bug in a cereal field depending on the distance to a forest edge (Shapiro, 1959). The
percentage of the parasitization was as follows: beside the edge - 65.1%, on the distance 100
meters - 61.3%, 200 meters - 52.2%, 500 meters - 32.0%.
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
2.6.1.5. Cultivation of plants in climatic conditions that suppress plant pests
These practices are known concerning growing of the potato in areas with climatic
conditions, which suppress aphids – vectors of virus diseases of this crop. This is the need for
obtaining the tubers free from virus infection, when usage them as a seed stuff. The vectors are
the aphids. In areas with cool and wet climate, these insects are affected heavily by fungal
pathogens, and therefore stay on Insignificant or Zero densities. Here are several examples of
such practices.
J.H. Fidler (1949) has reported that in Britain, "… production of high-grade seed potatoes at
north-east Yorkshire in land over 400 ft above sea-level" is conducted due to "nearly the
complete lack of the aphids until the end of July."
In Ukraine, T.T. Khandyborenko (1981) recommended to grow seed stuff of the potato in the
Carpathians Mountains on the altitude over 800 meters above sea-level. On such heights,
environmental conditions for growing of the potato are quite favorable, whereas vectors of
phytopathogens nearly completely absent.
The same reasons are reported to be the ground to grow potato as a seed material in
northeastern Provinces of France (V.P. Vasil’yev, pers. comm.).
It occurred to be the above practice to keep the potato free from viruses has been known to
people from ancient time. In fact, P.M. Zhukovsky (1964, pp. 272-273) reported that in South
America (in Bolivia, Peru), the potato for sowing was cultivated over centuries in areas situated
on 4000 meters above sea-level. In these areas, the potato sometimes suffers due to late (spring)
frost, i.e. this area is outside of the climatic optimum for the potato. However, the areas are
unfavorable for vectors of phytopathogens. Therefore, the tubers grow healthy. For the food
purposes, the potato has been cultivated in more favorable for this crop climate – in the range
1800-2500 meters above sea level (Ibid.).
Further, P.M. Zhukovsky reported that in Chili, until the middle of XX century, a producing
of the potato for sowing was limited by the Chiloe Island (42º of the southern latitude) with fresh
and wet climate, unfavorable for the vectors.
The above case stories are examples of usage CESPPs 2.3. "Routine weather suppression."
2.6.1.6. Simulation of the conditions analogous an operation
of 2.4. Periodic (bottle-neck) suppression
In the glasshouse culture, it is used a routine practice, which might be considered as a full
analogy of CESPPs 2.4. "Periodic (bottle-neck) suppression" operating in Nature. The practice
consists in a stopping of crop growing in summer, when it is not need in keeping of the
glasshouse culture. In so doing, the room is cleared out from growing plants, while its inner
surface and the soil are treated with pesticides. This practice decreases significantly a damage by
PPs.
2.6.2. Artificial measures of long-lasting character
CESPPs 2.6.2. embraces the following subcategories:
2.6.2.1. Eradication of plant pests by mechanical means.
2.6.2.2. Eradication of plant pests by release of sterilized individuals or breakage of
pheromonal communication.
2.6.2.3. Change of cultivated crops.
These measures are considered the remarkable reviews, in particular R.L. Rabb and
F.E. Gutrie (1970), H.C. Coppel and J.W. Mertins (1977), and E.F. Knipling (1979). In them, it
was described in detail case stories, analyzed their advantages and disadvantages.
There are a number of examples of successful usage of CESPPs 2.6.2. "Artificial measures
of long-lasting character" for saving from burdensome PPs. The measures concerning
phytopathogens were shown above.
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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 to insect herbivores, a good example is offered the case of the cotton boll weevil,
Anthonomus grandis Boh. This pest invaded from tropical America was very destructive at the
end of XIX and at the beginning of XX centuries in the South of USA, where the monoculture of
the cotton was practiced. "Diversification of crops has come into practice, however, where the
cotton crop has suffered, so that in a number of the affected States the total value of the crops
after the appearing of the weevil, has been greater than before" (Fernald, 1926, p. 141).
Especially successful the method occurred to be in the State Alabama, where the damage due to
the weevil provoked to grow a number of profitable crops – the pea-nut, the corn, the potato, the
sugar cane, and others. Grateful people even erected a monument to the weevil.
The usage of CESPPs 2.6.1. "Promotion to ecosystem stability by means of exploiting of the
ecosystem stability components of the categories 2.1., 2.2., 2.3., 2.4. per se or with
modifications", and CESPPs 2.6.2. "Artificial measures of long-lasting character" allows to
maintain ESPPs of articenoses on the level A.3.1. "Proper control."
2.6.3. Temporary suppressive measures
If CESPPs 2.6.3. "Temporary suppressive measures" is used as a routine means in the
conditions of high probability of the increase to keep density of herbivores and affection by
phytopathogens on Zero or Insignificant levels, this is a situation analogous to the level ESPPs
3.1. "Proper control."
2.6.3.1. Cultural practices with the aim to control plant pests
In agriculture, "Cultural practices include destruction of host crops after harvest…land tillage
to destroy soil inhabiting species, crop rotation, and planting time to escape peak emergence
patterns of insects" (Knipling, 1979, p. 565). This quotation demonstrates usage of the category
of CESPPs – A.2.1.2.1.1. "Superevasion from herbivores." Indeed, crop rotation and planting
time to escape peak emergence patterns of insects provide an operation of CESPPs A.2.1.2.1.1.
The other practices are of artificial character, having no analogy in nature.
2.6.3.2. Sanitary measures
"Sanitation is needed in pest control practices" (Knipling, 1979, p. 401). This is true for all
the kinds of pest organisms – PPs, household, industrial, human and cattle pests. Sanitation
limits their food resources, breeding stuff, sites of spending of inactive period in the life cycle,
shelters etc. The practices in this field are very diverse, and they have been well described in
literature, especially in old text-books, for example in the book by H. Martin (1928, Ch. XV).
2.6.3.3. Temporary suppressive measures sensu stricta
This is the usage of pesticides with the aim to control PPs. In spite of numberless critique of
the method, there are the situations, when it is irreplaceable. As an example of such a situation, it
might serve the problem is the damage of fruits by the codling moth, Carpocapsa pomonella L.,
which is able to destroy most part of the yield. Nearly all the apple cultivars do not have
Antibiosis against this pest. Natural enemies do not possible to suppress it neither in orchard, nor
in forest ecosystems (biocenoses). In the latter, fruits of the wild apple-tree, Malus silvestris
Mill. are damaged in the same rate as cultivars in orchards.
It is necessary a complete protection of all the yield of apples from the codling moth.
Therefore, application of insecticides to control this moth is practiced to keep density of the
moth on the yield on the Zero level. The control is not a response on increased density of the
pest. The control is conducted in advance of damage.
A protection against the fruit pathogen – the scab, Fisicladium dendriticus, which
depreciates the yield, needs treatments with fungicides. At last, the foliage should be protected
against the mildew, Podosphaeara leucotricha Salm
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
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Thus, CESPPs 2.6.2.3. "Temporary suppressive measures sensu stricta" are necessary to keep
the orchard on the level ESPPs A.3.1. "Proper control." Also, CESPPs 2.6.2.2. "Sanitary
measures" should be practiced for this aim. In orchards with other crops, the situation is similar.
The level ESPPs A.3.2. Lag control
2.6.3. Temporary suppressive measures
If CESPPs 2.6.3. "Temporary suppressive measures" is used as a response on increased
density of PPs, this is a situation analogous to the level ESPPs 3.2. "Lag control."
2.6.3.3. Temporary suppressive measures sensu stricta
The insect defoliators in forests (both biocenoses and articenoses), field crops and orchards
are able to reach often High density. Control of them needs in the time, when their density does
not reach this value. This is keeping of an ecosystem on the level ESPPs A.3.2. "Lag control."
The level ESPPs A.3.3. Late control
In articenoses, it is admissible the levels ESPPs A.3.1. “Proper control” or A.3.2. “Lag
control.” They are the cases, when 2.6.3. “Temporary suppressive measures” are practiced. The
level ESPPs A.3.3. “Late control” is out of human aims. Therefore, it needs not to consider such
situations.
Concluding remarks
The situations, which take place on the levels ESPPs 3.2. "Lag control" and 3.3. "Late
control", recall to mind something well known from the literature, namely: the level ESPPs 3.2.
"Lag control" – this is the H.G. Andrewartha and L.C. Birch’s (1954), and W.R. Thompson’s
"chance control" (Thompson, 1956 and a number of the earlier publications), whereas the level
ESPPs 3.3. "Late control" is the A.J. Nicholson’s "self-regulation in a population" (Nicholson,
1954). The Axiom 3 shows that these concepts are compatible. They both are true, but for
different circumstances.
The chance control operates in the situations, at which the level ESPPs 3.1. "Proper control"
is restored by activation of CESPPs of the Extrinsic class for a taxon of PPs. Often, this occurs at
onset of a definite weather. The farther a given area from W.C. Cook’s zone (a) for a taxon of
PPs, the greater a probability of such cases.
Also, the chance control can be exerted by sudden penetration into an ecosystem natural
enemies of PPs also by a chance.
When natural enemies of PPs are impotent due to absence of prerequisites of their activity,
and resistance of dominants also is unable to be restored, it enters in an operation the last
position of ESPPs – CESPPs 2.5. "Effects of crowding." This is the level ESPPs 3.3. "Late
control" or in other words – the "self-regulation in a population."
Moreover, the Axiom 3 demonstrates the existence of a situation, which occurred to be
unnoticed neither by A.J. Nicholson, nor by W.R. Thompson, H.G. Andrewartha and L.C. Birch,
namely: the upper level of ESPPs – 3.1. "Proper control", when no problems with PPs take place
as a whole. To explain, why PPs stay on the level below threshold of damage of their host-plants
is the main problem of population ecology.
When proper silvicultural practices at establishing of forest articenoses and at farther growth
of them are applyed, ESPPs of them is close to that in biocenoses, i.e. the former are able to
thrive up to the age of maturity and produce their regeneration without human assistence.
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G.I. Vasechko STABILITY OF TERRESTRIAL ECOSYSTEMS TO PLANT PESTS: AN AXIOMATIC APPROACH.
PART II. SUBSTANTIATION OF THE AXIOMS PROPOSED IN THE PART I
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