Insecticides in Agriculture S. A. ROHWER Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, Washington, D. C.
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There is general agreement that destructive insects cause tremendous losses; the figure currently used is $ 4 , 0 0 0 , 0 0 0 , 0 0 0 for an average year. Insect control presents many problems, the simplest of which is the correct concentration and rate of application. For development of insecticides cooperation of chemists, entomologists, and toxicologists is essential.
Estimates of losses caused by insects have been assembled by different workers at various times and i n various ways, but none have attempted to consider all the destructive species. N o t all insects are destructive; i n fact, many kinds are beneficial. N o summary has been made of the value of insects. A i l estimates of losses have dealt largely with the destructiveness of the better known important species that attack crops and products needed by man. The losses reported i n earlier estimates were restricted to comparatively few species. Large as these were, they were much less than the currently used figure of $4,000,000,000 for an average year. The wide difference between the estimated losses of today and those of some fifty years ago is due to many factors. Some introduced insects have become important destructive pests since the earlier estimates were made. Agricultural conditions have changed during this period and many native species are now causing heavy losses to crops which replaced their native hosts. I n storing and handling our agricultural products we have not taken steps to prevent losses. Some current practices make the products more susceptible to attack by insects and encourage multiplication of the pests. The public has become insect-conscious and rejects products which are infested. This increases loss and raises the standard for control. W o r m y apples, insect fragments i n cereals and canned products, are no longer acceptable. M a n y other changes i n our habits and methods of agriculture could be cited to explain the wide difference i n estimates that have been made of the losses that insects cause to agriculture. Irrespective of the method used i n preparing estimates of these losses, all investigators agree that the losses are tremendous. A few examples to illustrate this destructiveness have been taken from a report of hearings before a Congressional committee (1). Crop
Pest
Cotton
Boll weevil
Corn
Earworm Corn borer Weevils and moths Spruce budworm Black Hills beetle Codling moth California red scale Mexican bean beetle Onion thrips Hornworm Cattle grubs
Stored small grains Balsam, fir, and spruce Ponderosa pine Apples Citrus Beans Onions Tobacco Cattle
Period
Average Annual Loss Dollars
1909-29 1946 1945 1946 1947 1910-20 1947 1940-44 1943-44 1944 1944 1944 1940-44
256,015,000 319,349,000 140,000,000 37,000,000 600,000,000 4,500,000 15,000,000 50,000,000 10,000,000 5,502,000 14,500,000 84,073,000 160,000.000
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AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
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Benefits from Insect Control
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Important as estimates of losses may be, information on the prevention of losses is of greater interest and significance. Measures developed by entomologists for the control of many important pests involve the use of several different procedures: following certain farm practices, using cultural methods, distributing natural enemies, applying insecticides, and using mechanical devices. Information on how control may be attained has been disseminated by many means, and an effort has been made to encourage farmers and others to use them. The extent of use has varied greatly and i t is well recognized that full advantage is not taken of what is now known on how to prevent losses caused by insects. A few illustrations of controls requiring the use of insecticides will show the benefits that have been derived where control measures have been applied. I n 1947 growers i n Louisiana who applied measures to control wireworms increased the yield of cane b y 20 tons per acre and the acre yield i n sugar b y 3500 pounds. I n 1947 the yield of potatoes treated with D D T insecticides increased as much as 3 0 % above the yield i n untreated fields. In U t a h the production of alfalfa hay has been nearly doubled i n areas where insecticides were applied ; and i n areas where alfalfa seed was produced the yield has increased by 6 0 0 % b y the timely application of insecticides. I n the latter case i t meant the difference between a loss and handsome profit. In 1948 the use of D D T insecticides for the control of the hornfly so increased the production of milk and meat that the county agents i n several states estimated the benefits to be worth $54,000,000. The 1946 cooperative control program against grasshoppers saved crops on 5,666,000 acres at an estimated value of $41,000,000. F o r each dollar spent $52 worth of crops was saved. The aerial application of D D T insecticides to 413,000 acres protected^ 1,500,000,000 board feet of lumber at an estimated stumpage value of $4,600,000. The estimated cost of protecting apples from codling moth is $25,000,000—it permits marketing a crop with an average annual value (1931-35) of $110,000,000. Without control the crop would be largely unmarketable. I n the years 1947 and 1948 the growers of lima beans i n a single county i n California increased their returns b y $7,500,000 by controlling wireworms.
Cost of Insect Control Satisfactory figures on the annual expenditure by growers for insecticides are not available. This varies from season to season, depending on several factors i n addition to the intensity of insect infestations. I t has been estimated that for the calendar year 1934 farmers and others paid about $25,000,000 for the more commonly used insecticides; for the same materials the cost i n 1948 would have been approximately $28,000,000. During this 14-year interval the use of agricultural insecticides had more than doubled. The estimated expenditure for insecticides i n 1948 approximated $60,000,000. Interest i n and appreciation of the benefits of insect control are thus apparent. Expenditures for insecticides alone are not an accurate index of the cost of insect control. M a n y control practices do not involve the use of chemicals. Where chemicals are used considerable labor is required. T o this must be added operation, maintenance, and investment costs of equipment needed to apply them. When these are taken into account the cost of control increases several times. I n 1938 Hyslop (2) estimated that the cost of controlling the more important insect pests was $142,927,000.
Problems of Insect Control The control of insects is no easy or simple task. E v e n for those species that are well known and for which control measures are fairly standardized, many things have to be considered. I n cases where the suitable insecticide is known, there is need for accuracy i n using the correct concentration and rate of application. T h a t is usually the simplest part of the operation. T i m i n g the application may mean the difference between success and AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
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ROHWER—INSECTICIDES IN AGRICULTURE
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failure. Proper application is also essential. N o t infrequently the task of control is further complicated by the presence of several pests. This may require knowledge of the compatibility of several materials, some of which may be applied at the same time, others a few days later. W i t h these and other factors, and the variability that is associated with ail biological activity, there is need to keep i n mind the effect the materials may have on the plant or animal and the product which is being protected. Are the materials safe and usable for the purpose for which they were intended? is an ever-present question. Entomologists have had these and various other questions before them i n developing measures for control. They are fully aware that answers cannot be determined i n short order, and that the solution of a problem for one area does not mean that the answer is applicable to all parts of the country. Experimental work has to be done when the insects are present and during the limited active period of the stage of development when the treatment may be applied. This frequently means that experimental work can be done only during a few weeks within a year. Standard control practices developed within these limitations have taken all the v a r i ous factors into consideration. Entomologists recognize the inadequacy of many of the recommended control measures. They have initiated the effort to develop new and more effective insecticides and welcomed the interest and assistance of others. The recent accelerated development of new insecticides has opened new fields and done much to stimulate public interest i n insect control. M u c h more needs to be learned than to know that the new materials will k i l l insects, before their true worth can be determined. We must determine many things. Knowledge of the effect on beneficial insects, wild life, soil, and machines is important. Of greater importance is: Are they safe for the operator and for those who handle and use the product?
Cooperation in Development of Insecticides M a n y of the new insecticidal chemicals are complex organic materials with long and complicated names. There is need for simple common names. Without simplified terminology costly losses may result from relatively minor errors i n nomenclature. Coined names must be protected if they are to remain available for general use, and must be defined with sufficient accuracy to assure that a standard product will be marketed. Selection of such names requires cooperative consideration b y many agencies. Chemists can make important contributions to this undertaking. The complexity of the new insecticidal chemicals brings many other problems. S y n thetic organic chemicals are not effective against all pests. There is a marked selectiveness i n action even between closely related species of insects. Some insects have already developed resistance to some of the newer materials. The idea of insects developing resistance to certain chemicals is not new. The over-all principle is well established i n a few cases. The early development of flies resistant to D D T , a chemical which had been highly and universally effective for fly control, came as a surprise. Other cases of resistance to D D T are being indicated, and at least one kind of mite has developed resistance against another of the newer chemicals—parathion. W i t h chemicals that are as highly toxic to insects as some of the newer ones are, other problems arise i n the development of methods for their use. When only a small amount of a chemical is needed, ways must be devised to apply i t . The first of these is to determine how the chemical can be formulated into an insecticide. This is not a task for the chemist alone, because not a l l solvents, carriers, and diluents, even though suitable from the physical-chemical point of view, are equally effective entomologically. Here the chemist and entomologist must work together. The more closely and understandingly they cooperate the sooner the answer will be developed. When the new materials are developed, there is still the need to determine that they can be effectively and properly applied. This requires investigations i n the field of application equipment—sprayers, dusters, etc. The standard machines for handling large volumes of insecticides are not suitable where the dosage is reduced—as i t can be—to amounts as low as a gallon of finished insecticide per acre. AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
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The development of new insecticides means even more. It requires appraisal of the effect of the material on the operator i n all stages of use. It involves knowledge of the amount of residue that may remain on, or in, the part of the product that is used as food for man or beast and the effect of such residue on their health. Leadership i n such studies belongs to the toxicologist. The chemist, however, has a very important relation to these problems. He must supply the method for analysis and for removal of insecticidal residues. F o r some of the new insecticidal chemicals the entomologist has accurate information on their effect on insects. Suitable, satisfactory methods of analyses of the chemical and its residues await determination.
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Outlook for Insect Control The field of insect control is expanding; the need for it is better recognized and a p preciated. Agricultural development will i n future depend on pest control much more than i n the past, and it will be a salient part of the production and protection of agricultural commodities. Chemicals are essential for the control of many major pests. It is highly important that chemists whose part i n the cooperative effort is of increasing i m portance, increase their interest i n and understanding of the wide variety of problems. Entomologists welcome the opportunity to work closer with the chemists. The author, for one, is delighted with the expanding opportunities for developing the cooperative teams needed to find sound, safe, effective, economical answers to the numerous problems of insect control.
Seasonal Market for Insecticides I n general, the use of insecticides is seasonal, and the demand for them fluctuates greatly because the intensity of insect infestation differs widely i n various years. Peak seasons of infestations may be separated by years. The market for insecticides is, therefore, highly fluctuating; and success i n the business of producing and marketing insecticides depends i n no small measure on the ability to have the insecticide available at the time and the place needed. Production and marketing of insecticides offer a greater challenge to management and judgment than do many other fields i n the production of chemicals.
Literature Cited (1) Committee on Appropriations, House of Representatives, hearings before subcommittee on Department of Agriculture Bill for 1949. (2) Hyslop, "Losses Occasioned by Insects, Mites, and Ticks in the United States," Bur. Entomol. Plant Quarantine, Bull. E-444 (1938).
AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
