Ecological Considerations in Chemical Contror
Implications to Vertebrate Wildlife
By]
L. GE03.GE
OHN
School of Forestry, Pennsylvania State University
I am very happy to have this chance to discuss the
ecological implications of the use of chemicals on wild
vertebrates.
Although many factors affect wild populations, the introduction of pesticidal chemicals into wildlife environments represents a major ecological change
which is widespread, and which can be intense in its
effects at least on local populations.
firmed by laboratory tests. The LD 50 was determined
to be :rom 225 to 2,600 milligrams per kilogram for the
ring-necked pheasant, depending on the conditions of the
e:'(periment, and from 880 to 3,200 for the bobwhite.
More limited studies on red-winged blackbirds give an
LD SO of from 700 to 1,700 mg/kg (D. S. Dept. Int.
1963) .
Although chemicals have been used by man for many
years in the control of pests and hundreds of plants have
developed toxins which kill insects, current interest is
centered on the modern synthetic organic chemicals
(George 1957). DDT released to civilians shortly after
World War II was the first to be studied and there is
a considerable body of knowledge which has been learned
concerning its effects. This information is not speculative. It is not a matter of opinion. It is fairly precise.
There have been no thoroughgoing studies of the LD
50's 0: wild mammals, amphibians, and reptiles. Preliminary figures for cottontail rabbits would place the
LD SO at about 2,500 mg/kg (D. S. Dept. Int. 1963).
DDT will kill wildlife at various levels of application. This fact was determined in 1945 by a small group
of wildlife biologists working in cooperation with the
Division of Forest Insect Investigations of the D. S.
Department of Agriculture studying experimental applications of DDT for gypsy moth and other insect control (Cottam and Higgins 1946). They found that the
acute intoxication level for many birds is somewhere
between 1 and 5 pounds of DDT in oil solution per acre
as applied in forest environments. Later studies (Leffler
1958; Nelson and Surber 1947) have confirmed the
levels of acute toxicity of DDT to birds in forests to be
between 2 and 3 pounds of DDT per acre.
1 Paper No.
Research Unit.
114
sensitivities
have
The early studies with DDT indicated that forest
applications at 1 pound of DDT in oil per acre, if the
material were kept out of streams, would cause little or
no acute mortality of vertebrates.
'Vildlife is less intensely affected in the forest because there is a thick
strata in forest communities, the toxicant is not concentrated in anyone stratum, and applications ordinarily
are not repetitive.
Later studies of residual compounds were to prove that
these hopes were not always to be realized in that there
were the potentialities of harm even when applications
were relatively light (Barker 1958; Mehner and Wallace
1959) .
In the more intensive agricultural pest control a considerable number of pesticides were developed. At the
present time about 500 parent compounds are being used
in more than 50,000 formulations (PSAC 1963). Many
of these have proved to be more toxic than DDT in
laboratory
tests. Aldrin, fenthion, endrin, and phosphamidon are from 100 to 1,100 times more toxic to bobwhite than DDT. Some compounds may be more toxic
to one species than to another. Tests indicate that there
is a cO:1siderable difference even in closely related species often by factors of 20 or more in birds and 500 to
1,000 fold in fish (U. S. Dept. Int. 1963; DeWitt, personal communication;
Tarzwell,
personal communication).
Other compounds were much less toxic than
DDT.
Field studies of the effects of DDT have continued
and it is evident that to cause serious acute mortality,
applications must be: 5 or more Ib/ A for most mammals; between 2 and 3 Ib/ A for birds; around 1 Ib/ A
for reptiles and amphibians; and between 0.1 and 0.2
Ib/ A in oil solution for fish (Cope 1948; DeWitt 1956,
1958; George 1958a, 1959, 196Oa, 1960b; George et aJ.
1947, 1957; Keenleyside
1959; Kerswill
1956, 1957;
Kerswill and Elson 1955; Leffler 1958).
relative
This very general summation of the facts is discussed
in considerable detail in Fish and Wildlife Circular 167:
Pesticide- Wildlife Studies-A
Review of Fish and Wildlife Service Investigations During 1961 and 1962. It is
available from the Fish and Wildlife Service Washington, D. C, on request.
'
Even in aquatic situations early field studies indicated
that DDT applications of 0.1 Ib/A or less could be
applied at weekly intervals for as much as 10 weeks without serious acute mortality on the higher vertebrates,
although a considerable impact on the invertebrates, particularly the arthropods, was noted (Cottam and Higgins
1946; George 1960a; Tarzwell 1963).
A year later we were able to show that the route of
intoxication in this type of death was probably oral, not
dermal, as insects killed by 1 pound DDT/acre
applications in the field were toxic when fed to nestling birds
whereas direct application of DDT to nests, eggs, and/or
young, even at rates of 5 Ib/ A, did not produce mortality (George and Mitchell 1947). There were no tests
of respiratory intoxication in these studies. Additional
studies of routes of intoxication to wildlife in the field
are needed. Respiratory and dermal intoxication probably
are far more important than the early tests would indicate for many insecticides, particularly the organophosphorus compounds, and for big programs which cover
large areas.
Some of these
Lethal concentration studies of toxicants to fish indicate that the LC 5{) for such fish as the blue gill is
O.oI8 parts per million (D. S. Dept. Int. 1963).
been con-
of the Pennsylvania Cooperative Wildlife
78
Many of these birds which contained heptachlor epoxide
were collected well to the north of any known use of
heptachlor. At the start of the project we were fortunate enough to find seven refrigerated birds which were
co1lected in 1957 in Minnesota. These birds did not contain any heptachlor epoxide.
Selective toxICItIes also hold for classes of vertebrates
and various chemicals. Delapon, 2,4-D, 2,4,5-T, methoxychlor, carbaryl, and TDE are less toxic than DDT to
fishes, birds and mammals; fenthion, chlordane, naled,
dimethoate,
trichlorofon,
Kepone@ (decachlorooctahydro-l ,3,4-metheno-2H -cyclobuta [cd] pentalen-2-one),
lindane, malathion, and mire..x are less toxic to mammals
and fish; even parathion, highly toxic to birds and mammals, is less toxic to fish than DDT (D. S. Dept. Int.
1963) .
These selective toxicities make generalizations difficult,
but mortalities in the field today might well be restricted
to a limited systematic group, hopefully that of the target pest.
These data indicate that environments and wild species in the United States are contaminated with chlorinated hydrocarbons,
the most residual of the modern
synthetic compounds; but the United States is a relatively heavily treated area. What of the rest of the
world?
The geographic extent of the contamination is surprising. Even in remote parts of the world, far from
any known pesticide application, animals have been found
to contain residues. \"Iaterfowl, their eggs, and young,
collected in the far north near the Arctic Circle, were
found to contain DDT. This fact can be explained by
speculating that residues were picked up in some other
area before the birds migrated to the area, and it is
known birds can excrete or pass on pesticides to their
young in the eggs. The surrounding vegetation, however, also contained DDT (U. S. Dept. Int. 1963).
The question that I am sure most entomologists ask
is how serious is the chemical contamination of wildlife
environments?
What is the total impact on wildlife
populations?
Some years ago we estimated that about 100,000,000
acres were treated one or more times in anyone
year
(U. S. Dept. Int. 1960). This represents abut 50/0 of
the land area of the United States. On this area applications would approximate
a billion pounds of toxic
chemical, as something in excess of 1.1 billion pounds of
synthetic and inorganic materials are produced each year
in the United States and except for substantial amounts
of ])DT which are exported, most of these chemicals are
used here in the United States (Shepard 1958; Shepard
et al. 1960, 1962).
These acreage figures agree with the information
gathered on insecticide use by the special committee for
the Entomological
Society last year. The President's
Science Advisory Committee estimates 1 acre in 12 is
treated (PSAC 1963). Your committee indicated that
75% of the land in the conterminous United States has
never received any treatment (Hall 1962). This fact
might lead some to think the problem is limited to a
relatively sma1l percent of our total area. However,
such is not the case.
Fish and Wildlife Service biologists collected fish in
four watersheds on Prince of "Vales Island off Alaska.
This island is separated by the sea from the mainland
and was without any known pesticide application in the
past. Yet resident species of fish in two of the four
watersheds contained DDT (Hannavan,
personal communication) .
:Marine fishes from different oceans of the world have
been found to contain DDT: off the Scandinavian Peninsula, North and South America, and Asia. Some of these
species included pelagic, deep water fishes that rarely
come close to shore. Concentrations have been as high
as 300 ppm in oil (PSAC 1963).
These data indicate almost universal contamination by
pesticides. How this contamination occurs has not been
thoroughly studied in the field, but known difficulties in
application and physical factors of the behavior of DDT
could account for wide atmospheric dispersal, and food
chains, to be discussed later, could account for ecological
concentration.
Modern technology permits large acreages of wildlife
environments to be treated in their entirety in a short
time, and this has a considerable ecological impact on
wild forms. \;\/ildlife, unlike domestic animals, cannot
easily be moved from a treated area for a desired period
of time. Therefore, the only hope for survivors on a
large tract, treated at lethal levels, is on small untreated
islands in the treated area.
Some recent findings on residues will be of interest in
this particular respect. Thirty-one of 32 specimens of
bald eagles analyzed by the Fish and Wildlife Service
contained DDT and 75% of 2,300 samples of birds and
mammals from 22 states and three provinces of Canada
contained residues when analyzed. These animals were
not collected at random in a careful design; but a special
study of the woodcock met this difficulty.
The special species study of the woodcock was organized in 1958 because it winters in the southern gulf
states, the area being treated for control of the imported
fire ant, and it breeds in the areas being treated for control of gypsy moth and spruce bud worm in eastern
United States and the bordering provinces of Canada
(George, unpublished).
Also it is a bird which feeds
largely on earthworms, an invertebrate which has been
known to store pesticides in amounts sufficient to kill
birds feeding upon them (Barker 1958).
Other differences between domestic and wild forms
which make wild ones more vulnerable are: size-many
wild animals are very smal1, less than 2Q grams; metabolism, many wild forms are very active-birds
may
have heart beats of l000/minute and temperatures of
111of; adaptability-wild
forms may be very specialized
for a particular way of life, perhaps only one food item.
Biologists in a1l of the northern states and provinces
were asked to co1lect birds in the spring and in the fall
for analysis. In this way several hundred woodcock have
been collected. During 1961 and 1962, 190 of 280 of
these woodcock contained heptachlor epoxide, averaging
1.6 ppm, and 129 of 220 contained DDT, averaging 1.7
ppm. Since 1958, 322 of 469 samples have contained
DDT and heptachlor epoxide. These are fairly meaningful samples taken from Minnesota to New Brunswick.
As a result of these factors and the toxicity of the
compounds, outright death of wildlife can be predicted
after many applications dutifully following the label.
Some examples will now be described.
Applications of 2 pounds or more of dieldrin, aldrin,
or heptachlor for Japanese beeetle, white-fringed beetle,
fire ants, or other insects will cause severe mortality
79
(Scott et a1. 1959; D. S. Dept. Int. 1960, 1962, 1963).
In every area which the D. S. Fish and Wildlife Service
studied in Georgia, Alabama, Louisiana, and Texas there
was virtual elimination of ground level insectivorous
birds after application of 2 or more pounds of heptachlor
or dieldrin granules (D. S. Dept. Int. 1960, 1962). Curiously, upper stratum birds were little affected by the
applications. This would suggest that the type of formulation can restrict the ecological effects to one portion
or stratum of a wildlife community. This can be used to
advantage in the field.
Dutch elm disease applications may yield deposits of
from 1 to 17 or more pounds of DDT per acre and in
areas where the higher dosages are used insectivorous
species may be greatly reduced or eliminated.
Some
studies indicate the reduction of robins is more than
90% (Hickey and Hunt 1960; Hunt 1960; Mehner and
Wallace 1959; D. S. Dept. Int. 1960, 1962, 1963).
Orchards, formerly the habitat with the highest bird
population densities, are heavily treated with a variety
of pesticides and are no longer considered productive
wildlife habitat by wildlife biologists (George 1958a,
1959, 1960b).
Grasshopper control programs using two ounces of
aldrin per acre have been known to kill water birds and
their young (Eng 1952; D. S. Dept. Int. 1960).
Forest insect control programs using 1 pound or less
of DDT per acre have not been known to greatly affect
adult birds or mammals on an acute intoxication level
(Cottam and Higgins 1946; George 1959; George et a1.
1947; Nelson and Surber 1947; D. S. Dept. Int. 1960).
Repeated applications of 2 Ihl A reduced populations after
five years. Recent unpublished studies indicate reproduction of songbirds may be affected at 1 Ib/A. Valuable
sport and commercial fisheries are destroyed if streams
are treated (Keenleyside
1959; Kerswil1 1956, 1957;
Kerswill and Elson 1955; D. S. Dept. Int. 1960, 1962,
1963).
ment (D. S. Dept. Int.
munication) .
1963; DeWitt,
personal
com-
This leads us to another ecological field question the
entomologist might ask: How long does the chemical
affect wildlife in the field?
In the answer to this the class of chemical is, of
course! very important. The organophosphorus compounds
usually are quite ephemeral, especially in water; although in one study, parathion persisted for more than
9 months in orchard soils and was toxic in more than
75 miles of stream (Nicholson 1962). The chlorinated
hydrocarbons may last for years. This fact is important
because sometimes very dilute levels, even of relatively
nontoxic compounds, can cause difficulty by ecological
magnification. Treatment of Clear Lake, California, with
TDE at 0.14 ppm in 1949, and 0.02 ppm in 1954 and
1957 resulted in high residue levels in upper levels of
the ecological food chain, losses in grebe populations, and
poor r~procluction of grebes.
In December 1957, after the third application, 75 dead
grebes were counted. In January 1958 two sick grebes
were collected and autopsied. No pathogens were present, bet pesticide analyses indicated 1,600 ppm TDE, a
magnif.cation of 80,000 times. In March 1958 fish were
collected; residues ranged from 40 ppm TDE in carp to
2,500, a magnification of 125,000 times, in brown bullheads. Both are bottom-detritus-opportunist-feeders.
The
bullhead is nocturnal and more carnivorous. Also it has a
softer mucoid skin. Part of this difference in level of
residues may be a matter of adsorption. In July 1958
largemouth blackbass which had hatched 7 to 9 months
after the last application contained 22-25 ppm TDE.
The breeding population of more than 1,000 pairs of
western grebes, which were observed prior to the first
treatment, all but disappeared.
In 1958, less than 25
pairs were on the lake and no young were reported. In
1959, there were more than 15 and less than 25 pairs;
no nests were found; no young were seen. In 1962,
more than 50 pairs were present and for the first time
since 1957 more than one young was known to have been
produced.
Seed dressings of rice with DDT have killed and
reduced reproductive success of California pheasants and
dressings with endrin have killed fulvous tree ducks in
Louisiana and Texas (Hunt and Keith 1962; U. S.
Dept. Tnt. 1963).
Grebes are primarily fish-eating birds and are almost
entirely carnivorous.
They represent the peak of the
ecological pyramid of numbers in the lake. Secondary
predators seemed to be less affected and herbivorous fish
were said to contain less TDE than carnivorous fish
(Hunt and Keith 1962). Residues in 1962, 5 years after
the last application, were as follows: 253 ppm in fat of
largemouth bass; 379 ppm in fat of white catfish; and
up to 656 ppm in fat of western grebes (Hunt and Keith
1962). Much the same type of long-lasting toxicity and
death of birds has been noted in Big Bear Lake, Clayton
Lake, and Tule Lake, California, the Rocky Mountain
Arsenal in Colorado, and other areas (Hunt and Keith
1962; D. S. Dept. Int. 1963).
There is little need to further document wildlife loss
or survival. Numerous studies have shown losses or
survival agree with the general toxicity data cited
earlier. Many agricultural programs in crop lands and
those using pesticide fertilizer drilled into the ground
have not been studied. Some have suggested the latter
applications are less toxic, but no data are available.
Entomologists should know that it is difficult to census
wild populations and judge wildlife effects of pesticides.
Techniques for measuring field populations require considerable skill and time. Casual observations may lead to
incorrect conclusions. For example, replacement populations under certain conditions move into a treated area
and replace the original population which was there.
This replacement may happen very swiftly. Observers,
unfamiliar with habits of wildlife, might assume the observed animals are the original population and that there
has been no effect. In 20' x 50' enclosure tests designed
to study this phenomena one or both mates of 20 of 22
pairs of bobwhite died on ground treated with heptachlor
at 2 Ib/A. Average survjval time was 6 days within 2
weeks of treatment; 15 days at 1 to 2 months after treat-
Other factors affecting the duration of the effect are
the nucleus for reproduction.
In remote isolated areas
a stream may be impoverished for years. Such is the
case with at least two streams in northern New Brunswick after application for spruce budworrn control (Kerswill, personal communication).
Of course, specialized
forms v'ltih limited geographical range could be e.."(terminated. Freshwater
fish were said to be eliminated
from Cyprus after treatment for mosquito control.
In terrestrial
80
areas wild turkeys
have been known to
take 5 years to recover after a single application of
2 Ibl A of heptachlor (Clawson 1958; Clawson and Baker
1959). Other populations, particularly
rapid breeding
species such as rodents, rabbits, or frogs, may recover
within a year on some areas and have been reported to
be very numerous on certain areas after treatment for
fire ant control (D. S. Dept. Int. 1960, 1962, 1963).
The osprey, a speces feeding more commonly on living
fish, also has been found to have difficulty in producing
young in areas affected by pesticides.
Resistant populations of vertebrates have been developed. This has been suggested for frogs and fishes (King
1962; Vinson et al. 1963; D. S. Dept. Int. 1963). Resistant populations may carry higher residue levels and
cause undesirable food chain effects.
The peregrine falcon population in this country and in
Great Britain has declined notably in numbers and in
Britain, at least, this has been associated with pesticide
contamination (Moore and Ratcliffe 1962).
In Israel, the elimination of rodents by thallium led to
the almost total loss of predatory hawks and owls feeding upon the dying poisoned animals (Mendelssohn, unpublished) .
On the other hand, a woodcook wing survey which I
initiated during 1959 was based on the ability to determine age and sex by a study of wings, and study of
30,000 wings of autumn and winter shot birds revealed
1.8 immatures per adult female in 1959-60 and 1960-61
and 1.9 in 1961-62. This should ensure a replacement
population. Sex ratios were uniform each year. There
was no marked decline in total numbers as judged by a
continental cooperative singing ground count of several
hundred stations in the various northern States.
The entomologist will also be interested in special
problems of the ecologist which have been noted. For
example:
'Why is there such a tremendous species variation?
Bobwhite and ringnecked pheasants may vary by 100fold to several pesticides (U. S. Dept. Int. 1963) and pintails and pheasants may vary by SO-fold in susceptibility
to dieldrin (Rudd and Genelly 1956). Related fish may
vary by SOOor 1,000 times (Tarzwell 1963). This information makes it evident that certain species, partiClIlarly those with specialized habits, may be very susceptible in the field.
Studies of effects of carbaryl and methoxychlor have
not indicated any measurable change in field populations
of birds. Mirex, reasonably toxic to birds in laboratory
tests, has caused no difficulty which can be measured in
the field when used in a soybean oil bait on corncob grits
and used for the control of fire ants. On occasion pest
control can benefit wildlife, for example, the screw-worm
program.
Also, herbicides have been used to create
wildlife habitat. Possibly wildlife parasites can be controlled by pesticides.
Potentiation is another possibility in the field. This
is the synergistic effect of two chemicals. This has been
noted with dieldrin and DDT in woodcocks and preliminary results indicate it is true of other compounds.
Migratory wildlife would seem to be particularly susceptible to this difficulty.
Variations of susceptibility in age and sex groups is
another problem.
Young birds are sometimes more
susceptible or in any event they arc much smal1er and
therefore need much lower absolute amounts to kill.
Vigor and the amount of fat on an animal makes a big
difference in effect from one place and time to another.
These studies would indicate compounds and methods
are available which can be used without
serious
immediate effect on wildlife.
vVildlife ecologists hope that this trend can continue
and that in control of pests there will be efforts to retrict side effects by use of such knowledge as: ways of
life of various species; food habits; cover requirements;
geographic range; relative susceptibilities to toxicants;
strata occupied; response to attractants and repellents;
effects of time of year and time of day when chemicals
are applied; migratory
habits; amounts of chemical,
effects of formulation, and relative toxicity-to
devise
new methods of using chemicals safely. Also, alternate
means of control should be a part of our thinking.
During the breeding season, male ring-necked pheasants are several times more susceptible to toxicants than
females; but the bobwhite males show no such difference
(DeWitt, personal communication).
Could this indicate
the polygamous males are more susceptible to pesticides
and in general more expendable
than monogamous
males? The reproductive effect is important as wildlife
species are relatively short lived and some are very
dependent on annual population increase to maintain
their numbers.
I think the record is clear. Serious problems have
been shown to exist and no careful survey of total impact of chemicals has been made. With research some
of the most difficult problems have been solved. I hope
that we can look forward to the day when ecological
effects on wildlife and the total envronment will be as
much a part of the thinking and planning in pest control
operations as the effect on the target pest. This will
require serious, thorough-going
cooperative,
interdisciplinary ecological research of the effects of the important chemicals and formulations and pest control in different environments in selected areas of the country.
Wildlife biologists are not against a managed world.
They merely oppose unenlightened management. I hope
on this premise we can all agree.
Animals at the end of the complex ecological food
chain seem particularly vulnerable.
Only 3,807 eagles
were found in the January 1962 survey, which included
al1 States other than Alaska. Immatures constituted 24')'0
of the population. The 1962 breeding survey provided
data on 515 nests, of which 257 were in Florida. Overall
nesting success was 44% and at least 228 young eagles
were added to the population. But no successful nests
were reported for New England south of Maine, and
nesting success was exceedingly poor in the Central
Atlantic States. In New Jersey, 1 of 6 nests produced
young. In Maryland, not one of the 15 nests under observation was successful. In Virginia, 2 of 18 nests succeeded. The marked lack of breeding success in coastal
areas that are treated frequently for mosquito control
has led some conservationists to suspect that since dead
and dying fish are a major item in the eagle's diet,
eagle reproduction has been inhibited by DDT residues
accumulated by feeding on contaminated fish.
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and birds.
Audubon
Ecological Considerations in Chemical Control
Implications
to Nontarget
By
RICHARD
L.
Invertebrates
DOUTT
Department of Entomology and Parasitology
Division of Biological Control, University of California, Berkeley
It is becoming increasingly clear to entomologists that
some of our current pest-control procedures and attitudes must be modified. This necessity is brought about
not as a result of criticism of chemical control activities
by highly articulate sources, but instead is being forced
upon us by practical necessity. The distressing problems
of resistance, of residues, of resurgences, of harmful
effects on animals other than pests have become painfully familiar to every agricultural
entomologist who
must develop effective control measures for pests. His
dilemma is that on the one hand he is faced with these
very formidable problems attending chemical control,
and yet on the other hand he must use insecticides to
insure the continued production of certain crops as a
commercial venture. Since World \Var II these troubles
have increased in frequency and intensity, and it is
therefore especia\1y ironical that these difficulties have
become most severe during the one period when entomologists were applying the most powerful array of pesticides that have ever been made available for use.
an ecosystem composed of some very complicated biotic
communities to which one cannot with absolute impunity
apply a toxic chemical. Our teacher is Nature herself,
and she has been offering these lessons on the disruption
of ecosystems on every farm, field, and forest in America. Her course of instruction is replete with convincing
demonstrations of the fundamental balance of nature and
the beautifully functioning interrelationships
that e..'Cist
between species. vVe would be dull pupils indeed if by
now we had failed to grasp the fact that our pest species exists not only in a physical environment, but in a
biotic one as well, and that the pest forms only one part
of a very complicated web of interacting forces. The
application of powerful pesticides has frequently demonstrated, sometimes in a most startling and astonishing
manner, the presence and the role of other invertebrate
components of this community; species of whose e..'Cistence we were scarcely aware and of whose importance
in the communal economy we were entirely ignorant.
A typical case is that of certain LeCallilll11 species on
English walnut in California.
Prior to the advent of
DDT these scales were seldom encountered and their
density was so restricted that there was little to indicate
that their natural enemies, particularly small hymenopterous parasites, were responsible for this condition. The
importance of these parasites as controlling agents of
the scales became apparent when DDT interfered with
their effective action. The Lecallilll1l species that previously presented no problem became major pests of walnuts and the fact that this potential existed probably
would have escaped detection if it had not been for the
interfering action of insecticides (I\Jichelbacher 1962).
This effect of an insecticide in preventing the attack of
a parasite upon its host has its advantages, however, for
it has led to the development of a field technique, the
insecticidal check method, to measure the effectiveness
of a parasitic species. The so-called insecticidal check
plot is an area where an insecticide has been applied
In spite of all this, if we could project ourselves 50
)'ears into the future and view this period with the easy
wisdom that comes from retrospect, we might conclude,
rather surprisingly, that this set of problems associated
with the use of modern pesticides was actually very
beneficial, and was, perhaps, one of the best things that
ever happened to the profession of applied entomology.
It is quite possible that armed with such hindsight 50
years hence we would consider this period as a transition
from the age of innocence in the use of pesticides to the
era of enlightenment in pest control.
Education through trial and error is a notoriously
slow and often painful process, but this is the curriculum
to which applied entomology has been exposed. Through
experiences in using powerful pesticides, entomologists
have repeatedly demonstrated that no matter whether it
be a potato patch or a national forest it is nevertheless
83