Download Ecological Considerations in Chemical Control: Insects in the

Ecological Considerations in Chemical Control1
Introduction
By
Department of Entomology
RAY
F.
SMITH
and Parasitology,
Ulliversit'jI of California, Berkeley
Traditional
approaches to insect-pest problems have
centered on the development of techniques which attempt
to destroy pests as they appear in threatening numbers
and hopefully to eliminate them. These techniques have,
for the most part, involved the use of chemicals applied
with little reference to the complexities of agricultural
ecosystems.
In general, these control measures have
been successful. However, we must put certain qualifications on the success of these traditional approaches.
Their inherent limitations become clearer each year.
fundamental knowledge than does indiscriminate treatment with pesticides on specific dates or when the pests
first appear. A sound background is needed on the following points:
In recent months, it has been said many many times
that we must turn to new methods-especially
biological
methods--()f pest control and a few say we must eliminate the use of pesticides. I disagree violently. \\Fe
shouldn't eliminate any method that will help us in our
struggle with the insects. The present need is new perspectives in pest control and these perspectives with their
consequent new techniques are being developed.
It is obvious that no one management technique, e.g.
use of chemicals or introduction of biological control,
will be capable of handling all pest problems. A multiple
approach is needed which pursues all possible new leads
and utilizes all techniques to their fullest in an integrated
approach; this approach is of course what we have come
to call integrated control.
1) Why does the insect achieve pest status
2) The complexities of the crop ecosystem
3) The effects of managment procedures on all pest
species as well as the beneficial forms
4) An evaluation of the pest damage in terms of the
economics of crop production
I must
integrated
will be so
incorporate
ing as we
These new approaches have as their objective the mallagement of the pest pop1dation in such a manner as to
avoid economic damage rather than their complete elimination from a field or area. Of necessity, such pest
population management requires a much broader base of
] A s~mposium presented
at the St. Louis Meeting
Entomological Society of America, December 3, 1963.
of
stress that chemical control is a mainstay of
control. \Ve are dependent on chemicals and
dependent indefinitely. \\That we must do is to
modern ecological concepts into our thinkconsider chemical control procedures.
It is my opinion that our ecological view of chemical
control should be as broad as possible and our symposium panel will attempt to bring that broad ecological
viewpoint to bear.
the
Ecological Considerations in Chemical Control
Insects
in the Human
By
Department
MARSTON
Ecosystem
BATES
of Zoology, University of Michigan, Ann Arbor
Ecologists customarily divide the terrestrial environments of the earth into a series of major biomes: tundra,
taiga, deciduous forest, grassland, desert, and the like.
It seems to me that to this list should be added the
"man-altered biome" or "man-altered landscape," for the
environments in which human activity is the major determinant of the survival of organisms. The man-altered
environments are, to be sure, extremely diverse, including such different things as cities, gardens, orchards,
fields, rice paddies, managed forests, and abandoned
clearings. But there is one important common factor to
all of these: for survival, an animal or plant must be
able to adapt to the consequences of the actions of man.
habitats as little disturbed by man as possible. The result is a large area of neglect, which must be studicd if
the system as a whole is to be understood.
"Human ecosystem" is, I think, a better label than
"man-altered
landscape."
The idea of ecosystcms involves awareness of the constant interaction, interrelation, between organisms and environments.
'"\Then we
use a term like "biome" or "biological community" we
tend to think of a group of organisms in some particular
enviromuental setting, while actually the organisms are
constantly modifying the environment and vice-versa. To
cite an obvious example: the character of a forest depends in part on the soil type in which it is growing;
but the soil type is also, in part, a consequence of the
kind of forest growth. This kind of transaction between
organisms and the physical environment is constantly
taking place. In the case of the biological environment,
the vcry idea is based on the transactions between one
This man-altered
landscape is rapidly coming to
dominate the land surface of the planet, yet it is far
from receiving its fair share of attention from biologists.
The agricultural scientists tend to concentrate their attention on cultivated areas, while ecologists like to find
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organism or one kind of organism
things present in the neighborhood.
and
other
living
forward in man's control of the ills that afflict him; but
it is also a shift in ideas, a change in the conceptual
environment.
In a lecture given at Berkeley (Bates 1962), I attempted
to analyze the human environment-the
setting in which
man's actions take place. A common approach is in
terms of climate, inorganic resources, other organisms,
and the like. Or we can use a quite different method of
analysis. There is the perceptual environment-the
elements in the world around us that are interpreted by our
sense organs; the operational environment-the
elements
that influence us in some way, whether perceived or not;
and the total environment-all
the forces of the external
world including those, like radio waves from distant
stars, that have no detectable influence on our behavior.
It is curious that insects are very generally regarded
as pes:s, vermin, "enemies," by the peoples of Western
civilization. Even the attempts of entomo!ogists to stress
the "usefulness" of many kinds of insects meet with
little success. Nowadays one can argue that insects
transmit diseases, or that they are a major hazard for
scientific agriculture. But I suspect the Western attitude
long a:1tedates these discoveries. It would be interesting
to try to trace the history of this dislike of insects,
though I do not know how one would go about it. I do
think our attitude is unusual, if not unique. For one
thing, as far as I know ours is the only major culture
with a. strong taboo against eating insects (if we except honey, as an insect product).
We not only do not
eat insects-we
view the idea of eating them with horror. Yet we eat oysters, shrimp, lobster, and many other
marine invertebrates.
Why the taboo on insects?
In any such analysis as this, we quickly come across
the problem of how to deal with man's ideas. I first
thought of this as an environmental problem in relation
to the supernatural world that forms an important part
of the setting of any primitive people. For such people,
spirits are everwhere, in the bushes, the water, the
clouds. They can cause great damage by bringing on
disease, unleashing hurricanes, ruining crops; or if properly propitiated, they can be of great help in all sorts of
human enterprises.
We can laugh; we know that the
spirits have no "real" existence, that they are products
of the human imagination. But they are real enough to
the people concerned-just
as real as the sharks in the
lagoon or the leopards in the forest. In terms of influence on human behavior, they are far more important
than the visible animals.
But let's get back to the human ecosystem.
Man
clearly is involved in a series of relationships with other
organisms quite different from those of any other animal.
He has become, in fact, a sort of geological force,
moulding the landscape and determining the destinies of
a host of other organisms. ("Man's Role in Changing the
Face of the Earth" is the subject of a large symposium
volume edited by Thomas (1956).) How did he get this
way? And how can we classify the kinds of relationships he has developed?
We can laugh; but we have our spirits, too, only we
are likely to call them ideas. And these ideas, even though
they are products of our minds, constantly influence our
behavior. As an example, I have sometimes thought that
any word ending in "-ism" in English tends to denote a
malevolent spirit: Nazism, communism, Malthusianism,
McCarthyism, scientistism, perhaps even humanism. With
us, it is difficult to label such spirits as part of the
supernatural
world; it is better, I think, to call this
world of ideas surrounding every man the "conceptual
environment." This environment is the same thing as the
"culture" of the anthropologists,
and perhaps as the
"superego" of the clinical psychologists. But we gain a
different, and I think more useful, insight if we look at
it as an aspect of the environment involved in thc total
complex of the human ecosystem.
I like to think of the protohominids, of the early primates in the human line, as social carnivores.
Their
ecologkal relationships would then be similar to those of
the social canines, such as wolves. (Bartholomew
and
Birdsell (1953) have discussed the possible ecology of
these protohominids.)
As carnivores, they would have
been predators on other animals including I am sure
many ~:inds of insects-though
insects were' probably not
an important dietary element, at least after tools and the
skills to get large game easily were acquired. Animals
in the human line have also probably always had omnivorous tendencies, "scrounging" on all the possible food
products that they could digest, such as berries, nuts,
and fruits. Honey would fall in this "scrounging" category, and we have direct evidence of honey collecting, at
least since the time of the Magdalenian cave paintings.
This conceptual environment governs all om attitudes
toward other aspects of the world around us, and very
largely determines our behavior. The houses we live in
are very real parts of our physical environment;
but
their structure is a consequence of our ideas. This fact
applies equally to our clothing, the layout of our towns
and cities, our methods of agriculture.
Thes~ protohominids would not only get food, they
would m turn serve as food for other animals in the
community. They would be prey for such things as the
big cats and crocodiles; and hosts for many kinds of
parasites, including such insects as mosquitoes, lice, and
fleas. Man learned early to cope quite successfully with
large animals that might prey on him, but it is only
re~entIy that he has managed. to avoid, in some degree,
bemg food for these smaller msects.
At first thought this concept seems remote from insects.
But when we pause to consider, we realize that we cannot look at insects, or any other aspect of nature, except through the haze of our conceptual environment.
Witchity-grubs
are quite different things to the Australian aborigines who use them as a totem, and to the
European farmers who regard them as a pest. Termites
have one aspect if we look at them as a food delicacy,
and another if we look at them as destroyers of wood
constructions. House flies gain a new meaning when we
see them as possible vectors of disease. This is quite
rightly regarded as an advance in knowledge, as a step
The aforementioned would about complete the list of
basic relationships with other organisms until the time
of the Neolithic revolution-until
the development of
agriculture and settled village life, when a whole new
series of relationships started.
Most obviously, we have the relations with cultivated
plants and domesticated animals, organisms that can be
grouped together as "cultigens." \;Yith these man took
on a new role, becoming an agent of ~vo]utionary
change. The cultigens often became so modified through
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artificial selection that we can no longer be sure of the
nature of their wild ancestors. Some soon became completely dependent on human care for survival. Maize is
a classic example-it
cannot reproduce without someone
to husk the ears and plant the seeds. At least one insect,
the silkworm, belongs in the category of "obligate cultigens."
When man started to build shelters for himself, he
also inadvertently
provided shelter for a considerable
number of other animals, including many insects. Cockroaches and silverfish moved in on him, along with various rats, mice, lizards, scorpions, spiders, and the like.
Such animals can well be cal1ed human inquilinesanalogous with the inquilines of the nests of social insects. Whether things like bed bugs should be called
inquilines or parasites is a nice problem of definition.
Because they are associated more with the shelter than
with an individual host, I think they are better considered to be inquilines.
With the clearing of land for villages and fields, man
created a kind of situation otherwise rare in nature, an
open habitat. It is always surprising to get into a part
of the world where agricultural man has had no impact.
The common plants and insects of roadsides disappear or
can be found only in such open-habitat situations as
river sandbars. The weed and insect pests that get along
so happily with man simply cannot maintain themselves
in a closed community like that of the rain forest. I like
to call such organisms "opportunists" because they have
taken advantage of the opportunity offered them by
human action. Their association with man is much
looser than that of the inquilines of his shelters; but
like the inquilines and unlike the cultigens, they are unwanted associates. A great many insects surely belong
in this category.
man's role in the extinction of insect species, since they
attract less attention. The clearest case known to me is
the disappearance of the butterfly Lycaella dispar from
England, which seems to have been caused by the greed
of collectors (Ford 1945). I would suspect, however,
that many insect species have become extinct on oceanic
islands like the Hawaiian archipelago since the advent
of civilized man, simply through destruction
of the
babitat.
In a few cases, man has successfully exterminated introduced insect species through planned action (Mediterranean fruit fly in Florida;
AlloPheles gambiae in
Brazil and Egypt). But I can think of no case in which
he has succeeded in deliberately eliminating a native
species. The most elaborate attempt has been with
Allopheles labrallchiae in Sardinia (Logan 1953), but
while tbe species was enormously reduced in numbers, a
few specimens were found each year.
Probably other kinds of relationships between men and
insects could be found. Trying to work out such classifications can become an interesting and instructive game.
But here, in closing, I would like to point out two quite
different aspects of the human ecosystem-man's
gradual
withdrawal, with the development of civilization, from
association with any particular biological community;
and man's tendency to simplify energy exchange within
the man-dominated system.
Biological communities are ordinarily recognized in
terms of food relations-who
eats whom. \Vith man's
development of trade, transport, and storage, however,
this relationship has lost all meaning. If food differs in
Saint Louis, New York, London, and Paris, it is for cultural, not biological reasons. Conversely, it is interesting
to look at any meal, and speculate about the different
parts of the world from which the materials have come.
This trend is relatively new, dating at most from the
urban revolution that started some 5,000 years ago. The
Neolithic village was still associated with a particular
biological community-grassland,
forest or sea coast.
The modern city has lost all such association; the human
ecosystem has become a global network.
In any general survey of the relations between man
and other organisms, we would have to consider pets.
These, by my definition, differ from cultigens in that
they have not been modified by many generations of
breeding under human supervision. This sort of definition has interesting consequences. Dogs and goldfish
would have to be classed as cultigens, whereas cacti
planted in rock gardens would be pets. Insects have had
a limited role as pets in this sense. One thinks of children with rhinoceros beetles or dragonflies tied to
strings, or of fireflies used for ornament or il1umination.
The Meliponiine bees kept by Indians in tropical America (Bennett 1964) would be pets rather than cultigens;
and one can argue about the extent to which the honey
bee has become a cultigen rather than a pet.
The simplification of energy exchange is more relevant
to our present topic. With the development of cooking
and especially with the invention of pottery containers
for boiling things, man could utilize a wider variety of
vegetable materials than before. His digestive system is
not adapted for the breakdown of the cellulose walls of
plant cel1s; but this breakdown can be effected by cooking, which thus becomes a sort of outside c.'Ctension of
the digestive process. Man could then move from the
relatively inefficient position of predator to that of firstorder consumer, living directly on plant products. With
agriculture, he replaced vegetation he could not use or
did not want with vegetation that he could use; he
started restructuring the system.
With the development of civilization, man has increasingly become an agent of dispersal for other organisms;
and an agent of extinction. Charles Elton (1958) has
written an excellent summary of man's actions as an
agent of dispersal: and here insects are prominent. As
every entomologist knows, a large proportion of the
important crop pests in different parts of the world have
come from somewhere else, inadvertently transported by
man. And nowadays purposeful introductions are frequent-attempts
to establish predators or parasites of the
introduced pests.
Where man has remained a predator, a carnivore, he
has become a second-order consumer. He raises maize
for hogs or grass for cows, and eats the hogs or cows.
Only with fish is he a higher-order consumer; and fishing, curiously, has not changed much since the Neolithic; it remains a gathering process.
As an agent of extinction, man's actions are easy
enough to document for birds and mammals. For each
of these he has been the direct or indirect cause of the
disappearance, on the average, of one species every year
during the present century. It is less easy to document
The ordinary biological community is a complex network of organisms using each other for food in all sorts
of ways. Any time an ecologist tries to diagram this
complex by drawing arrows from the eaters to the eaten,
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he ends with a blur of criss-crossed lines. The idea of
"food chains" in nature has long been abandoned-they
are "food webs." But man has reached the point where
he will not willingly share his food with anything else;
he will not tolerate "worms" in his apples or foxes in
his chicken runs. He has set out, in other words, to
eliminate competition, to establish short and simple food
chains ending with his consumption. He even tries to
defeat the decomposing system by burying his dead in
metal-lined caskets.
ethic. As for esthetics, variety is generally more pleasing than uniformity, and for our own pleasure and
edification, we need to preserve as much of the wildlife
of the planet as we can.
But this is no place to elaborate the arguments for
conservation. We cannot go back to the Neolithic, and
I doubt whether any of us would want to if we could.
Vie are stuck with a very large population and with the
need for efficient energy exchange to support this population. But in the long run it is likely that we would be
most efficient if we could work in accord with ecological
principles. As Francis Bacon remarked a long time ago,
"you cannot command nature except by obeying her."
We have become so dazzled by our accomplishments that
we tend to forget this truism.
But nature has been
arounc. for a long time, and it may even manage to survive man. It would be fine, though, if man could survive too.
This simplification of energy exchange is not only
efficient, from the human point of view, but it is necessary, to support the present enormous world population.
But it also has dangers. The complex system of the
natural community is a stable system, while the simplified human system is much more liable to catastrophe.
Insect activities illustrate this fact very well. A disastrous outbreak of a particular species is very rare in
a natural community. The whole system of checks and
balances operates to keep the population of anyone species well under control. But in the human ecosystem,
the large areas of single crops are often liable to destruction by some herbivorous insect multiplying in the
absence of the parasites and predators that would ordinarily keep its population in check. Hence the need to
be ever alert and to resort to chemical measures of control. The drawbacks and dangers are brought out in
other papers of this symposium.
REFERENCES
481·-98.
Bates, Marston.
1962. The human environment. The
HQrace M. Albright Conservation Lectureship, II.
Uuiv. California,
School of Forestry.
Berkeley.
22 pp.
Bennett, C. F., Jr. 1964. Stingless-bee
keeping in
western Mexico. Geographical Rev. 54: 85-92.
Elton, C. S. 1958. The Ecology of Invasions by Animals and Plants. John Wiley & Sons. New York.
18: pp., illus.
Ford, E. B. 1945.
Butterflies.
Collins. London. 368
pp. illus.
Logan. J. A. 1953. The Sardinian
Project.
Johns
Hopkins Press. Baltimore. 415 pp., illus.
Thomas, W. L., Jr. 1956. Man's Role in Changing
the Face of the Earth. Univ. Chicago Press. 1193
pp., illus.
Elton (1958) has reviewed the evidence that the
diversity of species in the natural community tends to
promote population equilibrium in each species. This is
the utilitarian argument for maintaining as much diversity
as possible in the human ecosystem. There are also, as
Elton points out, ethical and esthetic arguments. What
gives Homo sapie1ls, here for perhaps 50,000 years, and
a major force operating on nature for 5,000, the right
to destroy a system that has been building up over many
millions of years? It can be said that he has the right
beca1>lsehe has the power; but in other situations most
of us do not consider "might makes right" to be a valid
Ecological Considerations
Insect Population
By E.
Associate
Professor
CITED
Bartholomew, G. A., and J. B. Birdsell.
1953. Ecology and the protohominids. Am. Anthropologist 55:
in Chemical Control
Problems
J. LERoux
of Entomology, Depart'ment of Entomology and Plant Pathology
Macdonald College of JIIIcGill University, Quebec
first biologists, forgot they were dealing with a class of
animals subject to the general laws of variability and
complex interrelations, and forgot their scientific obligation to seek explanations in terms of general conceptsto ask ~ow and why, as well as what and where. The
most striking support for this contention lies in the
failure of entomologists generally to anticipate the development of resistance to insecticides as a consequence of
one of the basic tenets of biology-the
principle of
natural selection." After 20 years of exposure to the pitfalls attendant on the use of chemicals for pest control,
without prior knowledge of their effects on populations,
we must as biologists charged with the solution of such
problem, make a complete reappraisal of our objectives,
The need for a fundamental approach to the study of
chemical control of crop pests is more urgently upon us
now than at any time in the past. For there is now a
great awareness on the part of everyone that the large
gaps that exist in our knowledge of pest problems cannot be resolved solely on the basis of the methods of
experimentation
that have been employed to date. Entomologists, generally, recognize the need for basic investigations but for the most part still pay lip service to
this need. ''Vhy is this so? A recent examination of the
problem in Canada has revealed, in the words of the
reporting chairman (Smallman 1964), that "During the
period of preoccupation with the application of control
methods, applied entomologists forgot that they were
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