Download Population Dynamics of Exotic Insects

Population Dynamics of Exotic Insects
B'j1
Research Institute,
TURNBULL1
A. L.
Canada Department
of Agriculture,
One of the most conspicuous features of introductions
of exotic species for biological control is that a large
proportion of even the most carefully prepared introductions fail. Though the organisms are usually carefully
selected for compatibility with known features of the
physical environment of the colonial site and known
foods are abundant in the new environment, only about
1 of every 10 introduced species succeeds in producing
viable populations in new areas, and many of these gradually diminish and disappear. The causes are unknown;
speculative reasons are usually given. Climate is the usual
scapegoat, especially in regions such as Canada, wh~re
winters tend to be severe, or California, where excessIve
heat or dryness is not unusual. But most species pass
rigid tests of these factors before they ~re. introduced;
thus these "explanations" tend to lack convlctlon.
These organisms were deliberately introduced into ca~efully prepared environments, and few would long survive
if deprived of tender loving care. Thus they cannot be
considered to be truly established on this continent in any
real sense of the word.
In addition to these organisms an even larger assemblage of organisms was accidentally introduced. For .this
group no sites were deliberately prepared; they recel.ved
no loving care, and were entirely dependent for survival
on thcir own resources. Many species of this group are
now thoroughly established in North America, and many
now constitute major problems.
Largely to combat this latter group, a further assemblage of organisms has been and is being introduced. This
group comprises organisms that are generally known as
agents of biological control. This third group. may be
initially cultured to some degree, but eventually Its membcrs too are cast loose to fend for themselves.
Another favorite explanation is that the new environment lacks some unknown but essential requisite of the
colonist species. If the critical element cannot be discovered, this explanation is not very satisfactory.
Another conspicuous feature of biological control introductions is the occasional species that establishes an
extremely viable population with great alacrity. ~~om
quite small colonies, often introduced under condltlo.ns
far from optimal, some species have achie;ed substantial
populations within a very few generatIOns.
Clausen
(1951) examined several of these cases and concl.uded
that fully successful exotic parasites or predators achieved
full commercial control of their hosts within 3 years or
Once an exotic species is thoroughly established in a
new environmcnt there is no reason to suspect that its
population dynamics differ in kind from those of a native
spccies. After all, exotic and nativc are relative terms;
many of our so-called natives originally made their way
hcre from other continents, after which time further
spcciation mayor may not have occurred. Thus, when
we speak of the population dynamics, or of any other fea-
3 generations of colonization. This conclusion means that
ture of exotics, we are rcferring to the processes that take
place during the establishment period. However, the estabIishmcnt period is of indefinite duration, and it is difficult to identify criteria that indicate when it is complete.
However, of the species introduced for biological control, considerably more factual observations of the colonization and early establishment
process are available.
Therefore, in general I propose to discuss some of the
problems of introducing exotic organisms for biological
1 Present
address: Dept. of Biological Sciences, Simon Fraser
University, Burnaby 2, B. C.
Ontario
control, to see if these problems have any general applications.
Exotic organisms playa very large role in our everyday lives; probably about 900/0 of the common ~oods produced on this continent as well as a large portton of our
fiber crops, ornamental flowers, shr~bs, .a~d trees, are
derived from plants or animals of exottc ongms.
lfost species that were accidentally introduced into
North America remained undetected for some time after
their arrival, and it was not until establishment was well
along that their presence and foreign origins were detected. A consequence is that very little is known of the
population processes of such species in their period of
colonization. There are, of course, a few exotic species
that made themselves conspicuous by becoming pests very
early after their arrival, and much is known about these
species. But these are a small minority and constitute
special cases. A far greater proportion have not distinguished themselves in any way and have become quite
innocuous ancl interesting components of our fauna. Confirmation of this phenomenon may be found in Lindroth
(1957). Most of you never have heard of most of the
species in his lists of European invaders of North America.
Belleville,
these insects built up their numbers from a handful to the
limit of their food resources within 3 generations. Clausen's observations were challenged on theoretical grounds
(Thompson 1951), but most subsequent experience supports his conclusions.
Less conspicuous but commonly occurring in the practice of biological control are the exotic species that successfully establish permanent populations on a. colonial
site only after a prolonged struggle. These specIes rarely
achieve any prominence in the new community, and usually form small localized or wides~re.ad, d~ffuse. populations. Their impact on the pre-exlstlllg bIOta IS small,
and they rarely achieve commercial control of their prey
(or host) pests. In the orthodoxy of biological contr?1
they are said to achieve "partial". control, on the b~sls
that if they are present on the sIte, and are attacklllg
pests, they must be contributing in some degree to the
suppression of pest populations.
The reasons for these differences have always
biological control workers. Most species seem
capable of thriving in the new territory, but the
mains that most of them fail to do so, even though
ous efforts are made to give them every advantage.
It
cies
cies
fail
333
baffled
equally
fact restrenu-
is highly probable that accidentally introduced spefall into the same categories. Undoubtedly many speof the potential immigrants that arrive in our country
to establish permanent populations. A much smaller
number establish small, localized populations that become
innocuous and interesting elements of our fauna. A wry
few of the species that arrive succeed extravagantly.
These latter species are often very disruptive of our native
and cultured communities and constitute some of our
most serious and damaging pests.
There is at present no known a priori way of predicting
into which category a potential immigrant will fall, nor
can we even say after the event why it turned out as it
did. Until we are able to supply such explanations we
cannot be said to understand even the barest essentials of
the population dynamics of exotic species, or to approach
intelligently the problems of either excluding damaging
exotics or of introducing beneficial ones.
TIlE
COMPETITIVE DISPLACEMENT
PRINCIPLE
There is a substantial piece of research published over
the past 5 years or so, which, though it has not escaped
attention, has a bearing on this problem that may have
been overlooked. This is the work of DeBach and his
associates on the introduction of various species of exotic
parasites of the aphelinid genus Aph:ytis to control the
citrus red scale in California (DeBach and Sundby 1963;
DeBach 1966). The phenomenon that DeBach observed
he has designated the "Competitive displacement hypothesis." The concept involved has a long history under the
names of "Gauze's law," "Grinnell's axiom," the "competitive exclusion principle," and various others. DeBach
and Sundby (1963) have reviewed the history of the
concept.
De Bach briefly stated the hypothesis as follows: "different species having identical ecological niches (i.e. ecological homologues) cannot co-exist for long in the same
habitat."
The process involved in this concept has been repeatedly
observed. When two species of closely similar habits, behavior, life histories, and, particularly, food needs are
confined in a homogenous, closed environment, one of the
species inevitably displaces the other. Which of the two
species emerges the victor seems to depend on the particular structure of the environment and on external
physical factors such as temperature, etc. On the other
hand, if two species that significantly differ in these respects are confined in similar environments, both can
co-exist indefinitely.
It was debated for many years whether this concept
was applicable to natural, free-living environments, or
whether it was a product of closed, artificial, homogenous
environments created in laboratories or in food-storage
depots. While there was little unanimity about it, the
general consensus seems to have been that it had little
significance, or if it had, it would be virtually impossible
to detect in natural environments. The concept was therefore considered by many to be less than helpful to the
understanding of natural populations. For many years the
hypothesis hung more or less in limbo, neither proven nor
disproven. It held an ambiguous place in the conceptual
arsenal of theoretical ecologists; it was frequently evoked
in theoretical discussions, but its evocation lacked consistency and was always open to challenge.
Now, through a series of patient and careful observations rarely equaled in the history of biological control,
DeBach and his associates have convincingly demonstrated that the process does occur in nonconfined, freeliving organisms, at least under certain circumstances.
What
DeBach observed
was essentially
this:
Apfryfis
clzrysolllplwli
(.Mercet), a parasite of California red scale,
was accidentally introduced into California about 1900,
probably from the Mediterranean region. By 1920 it .w:~s
widely distributed in the citrus areas of southern California over the range of its host. In 1948 A. lingllancl1sis
Compere was introduced from south China. This species
is very similar in every respect to A. chrysomPhali.
Immediately after A. lillgllallcllsis
was introduced it was
apparent that it was displacing A. chr.1'somPlwli near th,'
areas of release. By 1959 A. chr)'solllphali
was reduced
to a minor species surviving in small pockets only in the
south coastal region.
In 1956-57 another ecologically and biologically similar
species, Aphytis lIIclillUS DeBach, was introduced from
India and West Pakistan. It was shortly evident that ,"melinlls
was emphatically successful in interior areas,
where it rapidly displaced A. lillgllallcsis.
But though A.
1IlclillllS was thoroughly
colonized in coastal areas it
completely failed to established populations there, though
it was known that the climate in that area was eminently
favorable. Thus A. lillgllallcsis
continued to dominate in
coastal areas.
These observations revealed three occasions in which
displacement (or exclusion if you prefer) occurred: 1. .1.
lillgllallcllsis
displaced A. chrJ'somphali over most of its
range; 2. A. 1IlelimlS displaced A. lin91lUlll!IIsis in interior
areas; 3. A. lillgllallcllsis
displaced, or excluded, A. melililtS in southern coastal areas.
It is important to note that parasites of the red scale
other than Aph},tis species occur in all areas. Comperiella bifasciata Howard and Prospaltcllll
flcmieillsi
Tow,'r
are prominent among them. But these two species di ffer
from each other, and from Aplzytis species, in various
respects. Both of these species persist in all areas, hut
one is the more abundant in some parts of the range and
the other in the remainder. Neither was seriously disturbed by the Aphytis species.
These observations were accompanied by a series of
well-designed laboratory and field experiments which confirmed the observations and to a large degree explained
them. It was shown that when any two "ecological homologues" were brought together in a common environment
(a) one species always displaced the other within 8 generations; (b) the winning species could be altered hy
making small changes in the environment;
(c) displacement occurred in the presence of a surplus of food, i.e.,
food shortage is not a requisite for displacement;
(d)
differences in the relative fecundity and survival of immature stages, as reflected by the F, progeny production,
appeared to determine which species was the winner.
On the other hand, when two species "with only slight
ecological differences" were brought together in a common environment the results were ambiguous. In some
instances one of the species was displaced. In the lastmentioned cases either of the species could be the one
displaced, depending Oll external circumstances.
INTERPRETATION
OF COl\IPETITII'E
DISl'LACE1fENT
We now know that the processes which gave rise to
the enunciation of the competitive displacement principle
do occur in nature, at least under the exceptional circumstances of the coming together of closely related and
very similar species, each of which is endemic to widely
separated, mutually inaccessible areas of the world. The
only point in question now seems to be how this process
is interpreted.
334
Virtually all authors who have discussed the competitive displacement principle have done so in terms of identity of ecological niche. Indeed the two concepts, displacement and the niche, have represented opposite sides
of the same coin. Both concepts are generally considered
to have originated with Grinnell in a series of papers between 1904 and 1928. From an initial tentative statement
Grinnell progressively developed the idea into essentially
the same form that it is understood today.
In 1904 Grinnell stated "Two species of approximately
the same food habits are not likely to remain long evenly
balanced in numhers in the same region. One will crowd
out the other." By 1917 this tentative, much hedged statement had become "It is of course axiomatic that no two
species regularly established in a single fauna have precisely the sanll: niche relationships."
This statement,
which is much more positive than the former one, represents a solidifying and a narrowing of the concept.
Finally, in 1924 Grinnell defined the niche: "In studying
these matters I ha\'e come to use the term 'ecologic niche.'
This expression is intended to stand for the concept of
the ultimate distributional unit, within which each species
is held by its structural and instinctive limitations."
So here we have both concepts, competitive displacement and the ecological niche, unequivocally stated. No
one has since added much to these concepts.
We can see the developing logic that led to these con('epts. Empirical ohservations led to an initial, tentative
statemcnt. Twenty years later this statement solidified
into a formalized axiom. The concept of the niche was a
necessary invention to support the axiom. If we accept as
axiomatic that two species making identical demands on
an environment cannot simultaneously exist in that environnll'nt, we ll\ust conclude that each kind of organism
present in an association of organisms must possess a
uniquc set of environmental requisites. This is the niche.
The niche, therefore, is a collective term for all the
kno\\'n and unknown requisites of the species in a given
community. Thus if we spcak of species having identical
niches (i.e. ecological homologues), we are proposing that
two different kinds of organisms need precisely the same
things from the environment, down to the most minute
detail. This proposition seems extremely unlikely. The
tt~rms of the axiom itself preclude the possibility of two
sympatric species evolving identical niches. And for
allopatric species to evolve identical niches would surely
1'l'(juire that their ancestral stock possess equivalent evolutionary potential, and be subjected to identical environmental pressures in geographically separate areas. This
hypothesis seems to be pressing credulity too far. Even
though we might admit its theoretical possibility, we
would have to concede its extreme improbability, and
thus its very rare occurrence.
Now we do not know how rare the phenomenon of
rompetitive displacement is. But from DeBach's work wc
do know that it occurs. We also know that in this one
hiological control project it occurred three distinct times.
I suspect that this project was the only occasion in which
the interactions of introduced species with the resident
hiota were observed carefully enough to detect the process
of displacement.
If the process occurrcd three times in the single adequately observed case, it is probable that it has also occurred frequently in many other, less adequately observed
caSt's.
Therefore, competitive displacement may be a fairly
common occurrence, particularly in cases where species
that evolved in other associations are introduced to new
areas. This, of course, includes the case of colonization
of exotics. 1£ it is a common occurrence it is improbable
that identity of ecological niches is involved. Nor does it
seem necessary to the concept that the niches be identical
in all respects. If they are alike in only one respect, that
fact would seem enough. If two species share a single
common environmental requisite and one species for any
reason exploits that requisite more efficiently than the
other, this species should gradually take over a larger
and larger proportion of that requisite and thus progressively deny it to the other. Displacement would follow.
Grinnell tacitly admits this possibility in his early work.
In 1904 he talked of "two species of approximately the
same foods ... ." Foods may be an element of the niche
but they are certainly not the whole thing; identical foods
do not imply identical niches. Moreover, he applied the
adjective "approximately," meaning that even foods need
not be identical.
De Bach conceded the point more directly. He said "If
only one essential component of the niches of two species,
such as food, is identical, then these species have identical
niches insofar as food is concerned" (DeBach 1966). In
this statement, after defining the niche so that it is virtually all inclusive, De Bach contracted his definition to a
single element, to keep his formally stated axiom within
the bounds of reality.
However, DeBach states his position clearly, and I do
not quarrel with him. But the thing that concerns me
is why these authors, and most others that discuss this
concept, persist in talking of "identical niches" when they
are clearly referring to a single environmental element.
To do so places quite unjustified emphasis on the need for
exact identity of the two species. "Identical" is a precise
term,-it
means "exactly thc same." Different species
that have cxactly the same environmental requisites arc
hard to imagine, and if two such should mcet in a common environment neither could displace the other except
by chance, for neither could possess a consistent advantage.
It is a primary requisite of competitive displacement that
the two species must not be identical, but in fact must be
different. It is only by being different that one can win
and maintain an advantage over the other and thus
displace it.
As a result of this concern over exact identity, the concept of competitive displacemcnt has come to be considered a unique phenomenon of rare occurrence. Two species with identical niches must be rather rare, even if they
are siblings. Similar niches-yes; identical-no. On the other
hand quite different organisms that possess one or more
common requisites must be plentiful, and must frequently
meet in common environments when they are arbitrarily
moved about from one zoogeographic region to another.
For competitive displacement to occur, two opposing
conditions are necessary. The organisms involved must
have some (at least one) elements in common, i.e., there
must be some degree of similarity. On the other hand
there must be some difference between them. Now how
similar or different do they have to be? This cannot be
answered, except to say that the more similar they are,
i.e., the more elements they have in common, the more
likely is displacement to occur, as long as one difference,
no matter how slight, is left. Thus DeBach's Aphytis spp.,
which were very similar, were very vulnerable to displacement.
335
On the other hand, the less similar they are, the less
they have in common, and the less likely is displacement
to occur. Thus, in DeBach's work, Prospaltella and
Comperiella, which are substantially different, could coexist with each other and with Aphytis in some situations,
but in other situations either one could be displaced. Moreover, in some climatic zones Prospaltella was materially
more abundant than COlllperiella, and in other zones their
position was reversed. This fact clearly indicates to me
that these two species were competing to some degree
and that the advantage changed from one to the other
under the influence of changing environmental clements.
Therefore, these species could maintain a state of dynamic
balance, but at all times either one or the other, or perhaps both, may be suppressed below their maximal potential by competition, and both are in some danger of
displacement.
Seen in this light we can recognize that competitive
displacement is not a separate or unique phenomenon. It
is merely an extreme case of the general concept of interspecific competition, and can quite well be circumscribed
by that concept. It probably occurs frequently when species that evolved in different faunas are indiscriminately
mixed, because such species have had no opportunity to
evolve life processes that permit them to avoid competition.
RESISTANCE
OF COM1I1UNITIES
TO INVASION
Does this interpretation of the "competitive displacement principle," or the interspecific competition principle,
throw any light on the varying success of exotic species
in colonizing new territories?
I believe it does: most
exotics that seem well adapted in all ways to colonial
sites fail to secure lasting colonies. Is it because they
possess too many requisites in common with endemic
species and are thus "competitively excluded?" Is it not
to be expected that most long-established communities
will have evolved animals adapted to exploit most of
the niches that the community has to offer? Is it not
likely that species that have evolved under the precise
conditions of a given community will be more efficient in
exploiting the available niches of that community than
some exotic interloper that evolved in some other, different community? The probabilities all favor the incumbent species. Thus it is unlikely that many interlopers
can succeed; most will be rejected no matter how tolerant
they may be to the physical conditions encountered.
But the aforementioned conclusions are based only on
probabilities. The improbable cannot be excluded; it is
bound to turn up eventually. In the long history of introduction of exotic species it has turned up repeatedly.
Some immigrant species do have certain advantages at
least at times, or in certain parts of the community, that
permit them to achieve limited victories over resident
species. In these cases the advantage is rarely all on
one side, and a prolonged struggle may result which no
doubt generates heavy selection pressures on both organisms. Eventually either of the species may be eliminated,
or a measure of adaptation may develop through which
the two species divide the niche and thus minimize direct
competition. In the latter situation the invading species
can secure a firm but limited foothold in the colonial
territory with little opportunity to expand further. Most
of our established exotics fall into this category.
Finally, there are a very few cases where some immigrant species either possesses a distinct advantage over
an endemic species or where they find unoccupied niches
that they are able to exploit virtually free of competition.
Such species have an enormous advantage over endemic
species. The endemic fauna will be ill adapted to cope
with them, and normal community processes of hOI11('ostasis will be absent. Until they reach the limit of fond
resources their rate of population expansion is limited
only by their inherent rate of increase. Therefore, such
species become either major pests or major agents of
biological control, depending on their mode of life.
THE RELE\'AXCE
OF COMPETITIVE DISPLACEMENT
TO
BIOLOGICAL CONTROL
The relevance of the competitive displacement (or exclusion) hypothesis to the practice of biological control
is self evident. The importation of exotic entomophages
is the chief method through which biological controls are
practised in North America. The philosophy behind this
practise is that community stability is a product of the
diversity of the environment. By introducing many species of entomophages we hope to add to the diversity, an(!
thus to the stability of the community (Huffaker am!
Messinger 1964, p. 50, Balch 1960).
But the work discussed here demonstrates that the men'
introduction of a species to an already well inhabited environment is unlikely to increase the number of species
the environment supports. The results of introductions in
order of decreasing probabilities arc: the introduced
species is excluded by the competition of an incumhent
species; the introduced species divides the site with an
incumbent species; the introduced species displaces an
incumbent species; or the introduced species finds a vacant
niche and becomes established without displacing any
incumbent. Only in this last, and least probable situation,
is the diversity of any part of the site increased.
The displacement of
part or all of a site will
acter of the ecosystem
that such a change will
tion is remote.
one species by another in eithl"almost certainly change the charto some extent. But the chance
stabilize or reduce a pest popula-
I can imagine only two mechanisms by which an incumbent species would be displaced by an immigrant: the
immigrant directly attacks and demolishes the incumhl'nt
species; or the immigrant species 1110nopolizes some environmental requisite, thus denying it to the encumbent
population.
In the practice of biological control the
former situation is usually anticipated and avoided' the
second situation is probably the usual cause of displace~lent.
DeBach found that competitive displacement frequently
occurred in the presence of a surplus of food (prey). In
such cases some other niche requisite must be involved,
and whether a displacement based on some other resource
would increase or decrease the utilization of prey can be
only a matter of chance.
Therefore, DeBaeh's work may explain why so many
biological control projects have failed. The chances of
establishing a foreign entomophage in a new environment
are always small, and even if this hurdle is overcome the
chances of the immigrant's producing any beneficial ~ffcct
on pest abundance is also small.
Nevertheless, introduced entomophages historically have
produced conspicuous benefits in pest control. Long-shots
do occasionally payoff.
Whether the few successes obtained are worth the many failures inherent in such longodds gambling is debatable. Some rather imaginative
balance sheets of benefits and costs have been drawn up
suggesting that they are (DeBach 1964, p. 13). But anything we can do to shorten the odds will surely increase
336
our chances of success. As is usual in gambling situations,
shortening the odds consists of obtaining inside information. In this case we need information permitting us to
recognize vacant niches and the kinds of organisms that
arc needed to fill them; to understand the mechanics of
competition so that we introduce only organisms that
have some chance of establishment in the face of incumbent species; to gain some assurance that the immigrant
species, once established, will produce a beneficial effect
on pest populations.
single species-our
crop; not with stabilizing pests, but
suppressing them. For these purposes we seek specific
agents to carry out specific tasks. The chances of finding
such agents without knowing what characteristics
they
should possess are not impossible, but they are certainly
remote. In fact, we have little reason to suspect that stich
organisms exist.
REFERENCES
Balch, R. E. 1960. The approach to biological control
in forest entomology. Can. Entom. 92: 297-310.
Clausen, C. P. 1951. The time factor in biological control. J. Econ. Entom. 44: 1-9.
DeBach, P. 1964. The scope of biological control. In:
Biological Control of Insect Pests and Weeds. DeBach, P., and E. 1. Schlinger, cds. Chapman and Hall
Ltd., London.
1966. The competitive displacement and coexistence
principles. Ann. Rev. Entom. 11: 183-212. Annual
Reviews, Inc., Palo Alto, Calif.
DeBach, P., and R. A. Sundby.
1963. Competitive displacement between ecological homologues. Hilgardia
34: 105-66.
Grinnell, J. 1904. The origin and distribution of the
chestnut-backed chickadee. Auk 21 : 364-82.
1917a. The niche-relationships of the California thrasher.
Auk 34: 427-33.
1917b. Field tests of theories concerning distributional
control. Amer. Naturalist 51: 115-28.
1924. Geography and evolution. Ecology 5: 225-9.
1928. The presence and absence of animals. Univ.
California
Chronicle 30: 429-50. Reprinted
in:
Joseph Grinnell's Philosophy of Nature.
Berkeley
1943: 187-208.
Huffaker, C. B., and P. S. Messinger.
1950. Population
ecology-historical
development. It,: Biological control of Insect Pests and Weeds. DeBach P., and E. L
Schlinger, eds. Chapman and Hall Ltd., London.
Lindroth, C. H. 1957. The faunal connections between
Europe and North America. John Wiley & Sons,
New York.
Richards, O. W. 1955. Review: Andrewartha,
H. G.,
and L. C. Birch. The Distribution and Abundance of
Animals. Chicago Univ. Press, Chicago, Ill. ]. Anim.
Ecol. 24: 465.
Thompson, W. R. 1951. The time factor in biological
control. Can. Entom. 83 : 230-40.
The axiom that population stability is a product of the
diversity of the environment is a virtually self-evident
truth that is beguiling in its simplicity. As Richards
0(55) has said "It seems, at least to me, intuitively obvious that the bigger the complex of species involved the
more likely to be damped are the amplitude of the (population) fluctuations." But he also warned "it is perhaps
uncertain how far it is legitimate to apply general theories
to small segments of the whole ....
tt
This warning is
particularly apropos in the context of biological control.
The numbers and kinds of plants and animals in an
ecosystem are not simply a matter of chance; it is a characteristic of the ecosystem. This is not to claim that
specific sites support only populations of specific structure,
l'ither as to kinds or numbers of organisms present; extrcmely large variations of kinds and numbers are possihiL' on most sites. But the possible variations are not
infinite; they arc limited by certain environmental elemcnts and community mechanisms, of which competitivc
l'xclusion or displacement is one. The kind of species
that can colonize a given site depends to large extent upon
what specics arc already there, and the more species that
arc present, the more difficult it becomes for an immigrant
species to invade.
:Most of the communities into which we introduce exotic
cntomophages already possess populations nearing maximal
lliYersity. This fact applies even to those agricultural
lands in which species diversity has been deliberately imJlovl'rished. There is a limit to the number of kinds of
primary producers permissible if such lands are to maintain their agricultural productivity.
This limitation severely restricts all other forms of diversity, including
particularly the diversity of secondary consumers, i.e.,
entomophages. Thus we are being hypocritical when we
speak of diversity and stability in such environments.
Our objective is neither. We are concerned not with
increasing population diversity, but with maximizing a
EN'fOMOLOGICAL
CITED
BRANCH
JOURNALS
PACIFIC INSECTS.
A quarterly journal devoted
primarily to systematics and zoogeography. Vol. 1 (1959)
505 pp.; Vol. 2 (1960) 461 pp.; and Vol. 3 (1961) 589
!lP.: $7.00 per vol. to institutions and dealers, $5.00 to
individuals. Vol. 4 (1962) 996 pp.; Vol. 5 (1963) 945
pp.; Vol. 6 (1964) 770 pp.; Vol. 7 (1965) 922 pp.; Vol.
8 (1966) : $10.00 per vol. to institutions and dealers, $7.00
to individuals.
JOURNAL
OF MEDICAL
ENTOMOLOGY.
Quarterly journal devoted to all phases of medical entomology
from the world standpoint, including systematics of artho]lods of potential medical or veterinary significance. Vol.
1 (1964) of 402 pages; Vol. 2 (1965) of 396 pages: Vol.
3 (1966).
Subscription of $10.00 to institutions and
dealers; $7.00 to individuals. Prices in Japan Y3500;
Y 2500.
Order either of the above from Entomology Dept.,
Bishop Museum, Honolulu, Hawaii 96819 U.S.A.
MEETINGS
The Pacific Branch met at the Hotel Utah in Salt Lake
City on June 20-22, 1967. Chairman HOWARDE. DORST
presided at this fifty-first meeting. J. E. SWIFT was installed as the new Chairman while R. E. RIEDER was
chosen as Chairman-elect.
Secretary-Treasurer
W. W.
ALLEN and Governing Board Representative G. E. CARMAN continued in these offices. The next meeting will be
held at the Sahara Hotel in Lake Tahoe, California,
June 25-27, 1968.
The Eastern Branch met at the Holiday Inn in downtown Baltimore, Maryland on October 30 and 31, 1967,
with Chairman C. K. DORSEYpresiding. R. W. SHERMAN
was installed as Chairman for 1968 and R. E. Heal was
selected as Chairman-elect. Secretary-Treasurer
J. PETER
JOHNSONcontinued in that office. The next meeting of the
Eastern Branch will be in the Benjamin Franklin Hotel in
Philadelphia, Pennsylvania October 31-November I, 1968.
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