National Academies Press: OpenBook

Pest Control and Wildlife Relationships (1961)

Chapter: Wildlife - Pesticides Research Needs

« Previous: Pest Control in Public Health
Suggested Citation:"Wildlife - Pesticides Research Needs." National Research Council. 1961. Pest Control and Wildlife Relationships. Washington, DC: The National Academies Press. doi: 10.17226/18656.
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Suggested Citation:"Wildlife - Pesticides Research Needs." National Research Council. 1961. Pest Control and Wildlife Relationships. Washington, DC: The National Academies Press. doi: 10.17226/18656.
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Suggested Citation:"Wildlife - Pesticides Research Needs." National Research Council. 1961. Pest Control and Wildlife Relationships. Washington, DC: The National Academies Press. doi: 10.17226/18656.
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Page 21
Suggested Citation:"Wildlife - Pesticides Research Needs." National Research Council. 1961. Pest Control and Wildlife Relationships. Washington, DC: The National Academies Press. doi: 10.17226/18656.
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Page 22
Suggested Citation:"Wildlife - Pesticides Research Needs." National Research Council. 1961. Pest Control and Wildlife Relationships. Washington, DC: The National Academies Press. doi: 10.17226/18656.
×
Page 23
Suggested Citation:"Wildlife - Pesticides Research Needs." National Research Council. 1961. Pest Control and Wildlife Relationships. Washington, DC: The National Academies Press. doi: 10.17226/18656.
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Page 24
Suggested Citation:"Wildlife - Pesticides Research Needs." National Research Council. 1961. Pest Control and Wildlife Relationships. Washington, DC: The National Academies Press. doi: 10.17226/18656.
×
Page 25
Suggested Citation:"Wildlife - Pesticides Research Needs." National Research Council. 1961. Pest Control and Wildlife Relationships. Washington, DC: The National Academies Press. doi: 10.17226/18656.
×
Page 26
Suggested Citation:"Wildlife - Pesticides Research Needs." National Research Council. 1961. Pest Control and Wildlife Relationships. Washington, DC: The National Academies Press. doi: 10.17226/18656.
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Page 27

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WILDLIFE - PESTICIDES RESEARCH NEEDS Ira N. Gabrielson Wildlife Management Institute With the increase of industrialization and urbanization in re- centyears, wildlife managers have been faced with a familiar prob- lem stemming from an unfamiliar cause. The wildlife conserva- tion program has its beginnings in attempts to check the wholesale slaughter of beneficial birds and mammals by market hunters. The market gunner was outlawed and brought under control many years ago, but the wholesale destruction of wildlife by more modern agents still continues. The spectacular kills of birds and mammals, which are reported from time to time in the newspapers and more often in technical journals, are often accidental, but the end result to the animals involved is the same and such events occur frequently enough to cause serious concern among those who are interested in perpetuating the fauna of North America. Some of these wholesale kills involve the collision of migrat- ing birds with aircraft navigation beacons; others involve the entrap- ment of sea birds in oil discharge by ships at sea; and still others are the result of poisoning from ingesting chemical pollutants in watercourses. All of these are important, but one of the most serious problems, and one which is growing rapidly in importance, is the effect on birds, mammals and fish of widespread pesticide programs. The effects of chemical insecticides upon wildlife are very complicated. Frequently there is no immediate effect that can be noticed by observers. In the case of birds trapped in an oil slick, the cause and effect are both apparent. In the case of woodland area sprayed with a mist of heptachlor or DDT, birds may still be seen in the area and an extensive search may turn up few or no dead specimens. To all outward appearances, the area may be as at- tractive to wildlife as it was before the treatment and the lethal effects insignificant. 19

In analyzing the direct lethal effects of any product in the field, the observer is handicapped greatly by the normal behavior of a stricken animal. Many years ago one of my jobs was to con- duct and evaluate rodent and predator control programs. Even though we almost saturated some areas with toxicants in an effort to kill a rodent population, we rarely found many dead animals. As soon as the animals began to sicken from the effects of the poison, they crawled into holes or other hiding places, and only occasionally were numbers of dead animals found in the open. Eval- uating the direct lethal effect of a specific treatment, therefore, is very difficult, even when the object of the treatment is to kill the animals. When the object of the treatment is to control an unre- lated insect species, the problem of evaluation is even more acute. Significant though the direct kills of desirable wildlife may be, however, they are of far less concern to the biologists than the in- direct effects of the newer pesticides. In the first place, they are much more difficult to evaluate than the direct effects, and their importance may far transcend that of direct kills. Some of the newer chemicals remain toxic long after they are applied, and their lethal effect may be delayed for many months after the specimen is exposed. In certain areas where elms have been treated with DDT in efforts to eliminate Dutch elm disease, earthworms in the con- taminated soils have been found to have concentrated lethal doses of the chemical within their bodies. In some instances sufficient amounts of the chemical have been found stored in the bodies of earthworms to kill any bird that ate them, a full year after the spraying of the area. Another indirect effect that is just coming to focus involves the woodcock, an important migratory game bird that winters in the southern part of the United States, where they have been using hep- tachlor extensively in insect control. Heptachlor has been found in the tissues of woodcock killed in New Brunswick and Nova Scotia, the center of their breeding grounds, six months after they had left the South. Moreover, there is some evidence that young birds, which have never been known to be exposed to heptachlor, some- times have the substance in their tissues. Much of the research on this problem is being conducted and coordinated at the Patuxent Wildlife Research Center of the U. S. Fish and Wildlife Service in Laurel, Maryland, although the amount of money that has been available to date has been limited. There have been, however, some carefully controlled laboratory 20

experiments that indicate that many of the chlorinated hydro- carbons, in particular, decrease the reproductive capacity of birds and mammals. When very minute quantities of these chemicals are included in the diet of captive birds and mammals, their fertility is decreased. In the case of birds, the hatchability of eggs is sub- stantially decreased and the vitality of the chicks that are produced, and their ability to survive, also decrease. The parent birds, in spite of a steady diet which includes small quantities of chlorinated hydrocarbons, usually, show no ob- vious effects. They seem just as active as the control birds and sometimes lay normal sized clutches of eggs. It is often difficult to distinguish by the appearance of the birds the control pen from the pens in which the experimental birds were held. It was only in the reproductive capacity of the treated birds and the vitality of the second generation that the effects become apparent. A legitimate criticism of the use of many of the pesticidal chemicals is the fact that they are being applied without adequate knowledge of what they may do. Only one of the chlorinated hydro- carbons, for example, has ever been given a reasonably thorough testing before it was put into public use, and that was DDT. An entire series of tests were made of it by a cooperative team of wild- life specialists, entomologists, and chemists. Where recommenda- tions for the use of DDT are followed, there are no immediate ef- fects upon wildlife. Much of the present trouble with DDT and later members of the chlorinated hydrocarbon family of pesticides comes from their application by people who are incompetent to handle such lethal substances. Many feel that if the recommendations call for a pound of the substance to give effective insect control over an acre, five pounds should be five times as effective. I have personally seen and have had reported to me by competent biologists amazing ex- amples of carelessness and of complete violation of the instructions for the use of toxic pesticides. Most involved overapplication for the task at hand. There was relatively little conflict between agricultural pest control and wildlife conservation until the development of the chlori- nated hydrocarbons. The arsenical insecticides, which were the most prevalent type used before 1945, will kill birds and mammals if they ingest enoug'h of them, but most species have a relatively high resistance to arsenic and consume much less than is needed 21

to kill them when sprays are used in accordance with the recom- mendations of the entomologists. The organic phosphates are as deadly as the chlorinated hydrocarbons, but in most cases they lack their residual effects and stability after application. The pesticides of greatest concern to biologists are the newer chlorinated hydro- carbons, which are relatively stable and retain their toxicity much longer than any family of chemicals previously used for this purpose. The secondary effects of these are of greater concern to the biologist than the occasional spectacular kills of local wildlife populations that are reported in newspaper items. A serious handicap in studying the chlorinated hydrocarbons is the enormous variation in the toxicity of the materials to very similar species of wildlife. Only general statements can be made as to their effects. Fish and crustaceans are usually more susceptible than birds and mammals, and it takes much smaller concentrations to affect them adversely. But among the fishes, even those that are closely related, there is wide variation in the concentration of many chemicals that they can tolerate. No one knows why. All we know is that sue ha wide variation exists among the various species. The complications that this injects when safeguards are being evolved for the application of these substances are obvious. How do you recommend the spraying of a marsh area where there are four or five important species of fish, one of which may be 500 times as susceptible to the poison used as are the others? Studies are being conducted at the present time to find the answer, but they are in their early stages and they are not as many as are needed. At the outset it was felt that if we could get adequate toxicity tests started for the various species, we would have a beginning. Now it appears that we shall have to run toxicity threshold tests on all species before we can be certain, what is going to happen to a given area of marsh or stream when it is treated with a specific concentration of a given pesticide. On agricultural lands the problem is not as acute as it is on watered areas of forested lands. Most cultivated land is of neces- sity reduced to a simple ecological system, since one plant is favored over all others, a practice that incidentally favors pests but which produces generally unfavorable conditions for desirable wildlife. The same is true, although in a lesser degree, of open pastureland. 22

On all cultivated areas, therefore, the number of wildlife forms are much fewer than those which regularly use the "wild lands"—those which are neither intensively cultivated nor planted for pasture and hay. Such areas represent a complex ecological system and provide a habitat used by a wider variety of wildlife species. The most spectacular kills of wildlife through the appli- cation or misapplication of pesticides usually occur on such areas. In New Brunswick where a standard application of DDT was applied for spruce budworm control on the headwaters of the Miramichi River, a team of Canadian fishery biologists working in the area was able to observe and evaluate the effects upon the sal- mon. Since this team had been working there for several years, its members were entirely familiar with the existing and past age- classes of the fish population, and they were able to measure ac- curately the effects of the spraying operation. It killed from 80 to 90 per cent of all one- and two-year-old salmon in various sections of the stream. It also nearly obliterated the organisms on which the young salmon depended. It will be a year or possibly two before we have a complete evaluation of the over-all effect. This is only the most spectacular of many fish kills that have been traced to the application of pesticides. One of the approaches desired by all wildlife workers is a re- duction in the number of the broad-spectrum poisons that are being used and the development of specific poisons that will be toxic to in- dividual pests without endangering other species. One of the most interesting examples of what can be done is found in the develop- ment of a chemical that is being used to control the sea lamprey in the Great Lakes. The poison, which is being applied in the tribu- tary streams where the larvae lampreys live in the mud, kills only the lamprey without apparent adverse effect upon any other species. Yet it is being applied in an ecological environment where the use of non-selective poisons would be exceedingly dangerous to valuable fish resources and possibly to man. From the standpoint of the biologist, that type of control represents the ideal, and much more research should be geared to the development of pesticides that are specific in their effect on individual pest species. This is a tool that can be used with the precision of a rifle in eliminating a single pest from an ecological area. Under present shotgun techniques, beneficial forms of life are usually destroyed along with the prime target of the control program. 23

A second ideal method, in which spectacular success already has been achieved, is through the use of biological and cultural con- trols. The screw worm, a particularly unsavory parasite on cattle and deer in the Southeast, has been virtually eliminated through the saturation release of male screw flies sterilized by the use of radia- tion. Only a few weeks ago I inspected mosquito-control projects in Florida where successful control of salt-marsh mosquitoes has been effected through the use of water-level manipulation. Thous- ands of acres of impoundments have been constructed by authorities along the coast of Florida as the cheapest and most effective way of coping with the problem. Not only have the mosquitoes been con- trolled but the environment in many instances has been improved substantially for wildlife. The impoundments vary from 100 to several thousand acres, but each has one or more flood gates which permits control of the water level of the marsh. In each of these projects there has been close cooperation between the mosquito control authorities and the Florida Game and Fish Commission so that the opportunities to enhance wildlife habitat are recognized and followed up. The use of chemicals has been largely eliminated. The one drawback to this system has been that it has not proved entirely successful in controlling fresh-water mosquitoes which breed under different conditions than the salt-marsh species. It has proved successful against some varieties of the fresh-water species but not all of them. Additional research may find the ans- wer to this problem. The Florida salt-water marsh mosquito control program is highly significant to biologists since the estuarine waters affected are the breeding grounds of our most valuable food and game fishes. Either the adult fishes seek out bays, inlets and the mouths of streams to spawn, or the fringes of the marshes serve as vast nurseries for the larvae and fry of these fishes. In all of the im- poundments provision is made to pass fish over or through the dikes in order that their cycle of life may not be interrupted. These instances, however, are only the fringes of the potential that exists for improving present control programs. A vast amount of additional research is needed before the theoretical ideal of the biologist can be approached on a general scale; a tremendous im- provement in present techniques of distribution and application of pesticides is required before the biologist can rest easily. We need 24

desperately a wider public understanding of the secondary effects of chemical pesticides and the dangers that are inherent in the over- use and misuse of pesticides. No responsible wildlife biologist would advocate the abrupt prohibition of chemical pesticides, even if such a prohibition were within the realm of possibility. Properly used by responsible in- dividuals, they serve an important purpose. All that the biologists ask is that a greater degree of caution and responsibility be demon- strated all the way from the manufacturer down to the spray-tank operator and an awareness on the part of all concerned of the po- tential dangers of overapplication. We also ask that more attention be given by federal and state authorities concerned with pest con- trol in developing methods that will be less hazardous to beneficial forms of life. When the chemists produce a product that is specific for individual pest species, as they have already done with the sea lamprey, they will find the wildlife biologists leading the applause. 25

THE NATIONAL ACADEMY OF SCIENCES NATIONAL RESEARCH COUNCIL The National Academy of Sciences--National Research Coun- cil is a private non-profit organization of scientists, dedicated to the furtherance of science and to its use for the general welfare. The Academy itself was established in 1863 under a Con- gressional charter signed by President Lincoln. Empowered to provide for all activities appropriate to academies of science, it was also required by its charter to act as an adviser to the Federal Government in scientific matters. This provision accounts for the close ties that have always existed between the Academy and the Government, although the Academy is not a governmental agency. The National Research Council was established by the Academ in 1916, at the request of President Wilson, to enable scientists generally to associate their efforts with those of the limited member ship of the Academy in service to the nation, to society, and to science at home and abroad. Members of the National Research Council receive their appointments from the President of the Aca- demy. They include representatives nominated by the major scien- tific and technical societies, representatives of the Federal Govern- ment and a number of member s-at-large. More than 3000 of the foremost scientists of the country cooperate in the work of the Academy-Research Council through service on its many boards and committees in the various fields of the natural sciences, including physics, astronomy, mathematics, chemistry, geology, engineer- ing, biology, agriculture, the medical sciences, psychology, and anthropology. Receiving funds from both public and private sources by con- tribution, grant, or contract, the Academy and its Research Council thus work to stimulate research and its applications, to survey the broad possibilities of science, to promote effective utilization of the scientific and technical resources of the country, to serve the Government, and to further the general interests of science.

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