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held in the absence of air in quartz cells. Although no p , p ' dichlorobenzophenone JTas. isolated from the reaction products, hydrochloric acid developed in each solution tried, and in some cases crystalline proddcts of higher melting point than D D T were isolated. Benzene was found to be the most active solvent under these conditions also. The results of this work indicated that ultraviolet light will either catalyze the condensation of D D T molecules or cause it to react with the solvent. D D T presented a problem in residual action that was similar to the residue problems of the inorganic insecticides in that the residue carries through to the final consumption of agricultural products. The oil-soluble nature of this insecticide presents difficulties in residue removal that are not encountered with inorganic materials. D D T is hard to remove from apples and orange peels because it tends to remain, dissolved in the wax or oil of the fruit. The usual methods of washing to remove the residue are not so effective as Kith inorganic materials. Apparently D D T is an organic insecticide with too much residual action for some agricultural uses. It is expected that through studies of the chemistry of D D T there will be developed farm practices which make use of the known weak points of D D T , as well as others yet to be discovered, t o control the length of residual action of this organic insecticide. LITER 4TUQE CITED
(1) Bousquet, E. W.,U. S. Patent 2,123,929 (July 10, 1938). (2) Bushland, R. C., Schechter, M. S., Jones, H. A., and Kntphng, E. F., Soap S a n k Chemicals, 21, 119 (1945).
Vol. 40, No. 4
Chandler, A. C., Calif. Mosquito Control Assoc., Papers of 13th Ann. Conf., pp. 86-90 (1944). DeEds, F., and Eddy, C. W., J . Am. Chem. Soe., 60, 1446 (1938). Fleck, E. E., J . Econ. Entomol., 37, 853 (1944). Fleck, E. E., and Haller, H. L., IXD. EXQ.CHEM.,37,403 (1945). Fleming, W. E., and Chisholm, R. D., J . Eeon. Entomol., 37, 1.55 (1944).
Gunther, F. A , , Lindgren, D. L., Elliot, M.I., and LaDue, J. P., I b i d . , 39,624 (1946).
Guy, H. G., Del. Agr. Expt. Sta., Bull. 206 (1937). Haller, H.L., and Schaffer, P. S., U. S. Patent 1,945,312 (January 30, 1934). Jones, H. A., Gersdorff, W. A., Gooden, E. L., Campbell, F. L., and Sullivan, W.N., J . Econ. Entomol.. 26. 451 (1933). LaForge, F. B., Haller, H. L., and Smith, L. E., Cheh. Revs., 12, 181 (1933).
LaForge, F. B., and Soloway, S.B., J . Am. Chem. Soc., 69,2932 (1947).
Lindquist,, A. W., Jones, H. A., and Madden, A. H., J . Econ. Entomol., 39,55 (1946).
Lindquist, A. W.,Madden, A. H., Wilson, H. G., and Jones, H.A., Ibid., 37,132 (1944). Metcalf, R. L., and Wilson, C. E., I b i d . , 38, 499 (1945). Roark, R. C., I b i d . , 23,460 (1930). Roark, R. C . , U. S. Bur. Entomol. Plant Quarantine E-706, pp. 11-16 (1946).
Salzberg, P. L., U. S.Patent 2,112,381 (March 29, 1938). Tattersfield, F., J. A g r . Sei., 23, 396 (1932). Wain, 11. L., and Martin, A . E., A n a l y s t , 72, 1 (1947). West, T . F., .Vatwe; 152, 660 (1943). Wichmann. H. J., Patterson, 1%'.I., Clifford, P. -4., Klein, A. K., and Claborn, H. V., J . Assoc. O f i c . A g r . Chem., 29, 218 (1946). Zeidler, O., Be?., 7, 1181 (1874). RECEIVED Kovember 2 2 , 1947.
Insecticides for Pr
rowing Crops
Bailey B. Pepper ,Yew J e r s e y A g r i c u l t u r a l E x p e r i m e n t S t a t i o n , 'Vew B r u n s w i c k , il'.
Intensive research is required to evaluate the factors which are limiting the use of the new synthetic organic insecticides. The economic value of insecticides is discussed; new types of insecticides and their increased use have given the entomologist broader knowledge of the actual damage to growing crops by insects.
, P
RIOR to World War I1 the list of st'andard agricultural insecticides was relatively small. This list included: inorganic
chemicals-the arsenical and fluorine compounds; natural organic compounds-rotenone, nicotine, and pyrethrum; and a few synthetic organics-phenothiazine, xanthone, etc. Most of the synthetic insecticides made prior to the war had such minor advantages over t,he inorganics and plant derivatives that it a a s hardly worth n-hile to market. them. The int,roduction of D D T was the spark that started economic entomology on the march toward more efficient insect control. Had thjs wonder chemical never come into commercial use it would still be t.he greatest discovery in t.he history of entomology because it is responsible for the interest in research in agricultural chemicals. Practically every jnsecticide manufact,urer has launched a research program which is aimed a t an insecticide superior to DDT. Results have already been obtained in the discovery of chlordan, dichlorodiphengldichloroethane (DDD or TDE), chlorinated camphene, benzene hexachloride, and several phosphate compounds. Many promising insecticidal materials are still known only by laboratory code numbers. LIMITATIONS OF SYNTHETIC INSECTICIDES
iilthough progress has been made during the last few years in the development of synthetic organic, insect,icides, the inorganics
J.
and plant derivatives-arsenicals, rotenone, pyrethrum, and nicot,ine-cannot yet be replaced in their use against certain pests and where experience in their application has proved their value. The synthetic insecticides often give outstanding performance in insect toxicit,y: on the other hand, the following objections and/or limit,at,ionsare unknown factors connected with their use: specific t,oxicity (limited to certain species of insects) ; toxicit,y t,o man and animals; toxicity to plants; toxicity to beneficial insects and animals; and possible residual effect in the soil. SPECIFICITY.The farmer would like a single insecticide to control all species of insects at,tacking his crops whereas current trends indicate the development of an insecticide to control each insect or group of insects. D D T gives excellent control of cabbage caterpillars, leafhoppers, flea beetles, codling Moth, and Oriental fruit, moth, but the Mexican bean beetle, grasshoppers, plum curculio, and others are lit,tle affected by it. Chlordan, dichlorodiphenyldichloroethane, benzene hexachloride, methoxy analog of DDT, and hexaet,hyl tetraphosphate also she\\- high toxicity t o some species of insect's but are ineffective against others. However, each o f these chemicals is t,oxic to certain species against which the other materials are ineffective. TOXICITY TO klzx AND ANIMALS. All the new synthet'ic insecticides are considered t o represent a hazard to man and animals: t o the user during application, and t80tjhe consumer as a residue on food plants. As knowledge of minimum concenlrations, met,hods of formulation, and methods and schedules of application is gained, these risks can be great,ly reduced or eliminated. TOXICITY TO PLANTS. Each of the synthetic iusccticides, if used in sufficient concentration t o control a given pest, will injure some species of plant#. Such factors as soil, climatic conditions, and formulation of the insecticide influence phytotoxicity. It is the contention of the author that, entomologists
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INDUSTRIAL AND ENGINEERING CHEMISTRY
have been too concerned with killing insects to appreciate fully the phytotoxic effects of the synthetic organic chemicals. The fact t h a t the European red mite and the woolly apple aphid tend t o build u p in large numbers following the use of D D T suggests t h a t the chemical may alter the physiological activities of the plant attacked. Crop yield i’s the final criterion of the usefulness of a n insecticide, and there is ample evidence t o show t h a t yields of some crops are reduced when organic chemicals are used for pest control. I n New Jersey yields were reduced with the use of synthetic organic insecticides without the chemicals producing tangible signs of plant injury. The yield of tomatoes, sweet corn, beans, and certain varieties of peas has been decreased by D D T as compared to other treatments. The methoxy analog of D D T is apparently safer on cucurbits than technical D D T , yet it appears to be more phytotoxic t o tomatoes and corn than is D D T . This past spring, a preliminary experiment showed, almost without exception, that the synthetic organic insecticides applied t o tomato seedling reduced the set of fruits whereas most of the inorganic insecticides had no effect on fruit set. There is much to be learned about the phytotoxic effects of the new insecticides. It, seems possible t h a t methods of formulation can be found t h a t will reduce or eliminate the plant injury factor. Thorough testing on all crops prior t o the marketing of the insecticide is essential. TOXICITY TO BENEFICIAL INSECTS ‘AND ANIMALS. There is considerable debate on the question of the effect of these new insecticides on beneficial forms of animal life-especially parasitic, predaceous, and pollinating insects. Indications t o date are t h a t DDT is no more detrimental to the honey bee than arsenical insecticides. The fate of parasitic and predaceous forms is not fully known. Some investigators believe t h a t the rapid build-up of some insects following the use of DDT is due t o the destruction of the natural enemies of the insect in question. DDT and other new insecticides have not been used extensively enough fully to determine the effects on beneficial forms. It is known from laboratory tests that parasites and predators are killed under controlled conditions. Observations under field conditions also indicate t h a t beneficial forms of insects $re killed. However, there is reason to believe that these chemicals are so efficient against the pest species t h a t it will not appear in outbreak proportions even though its natural enemies are destroyed. POSSIBLE RESIDUAL EFFECT IN THE SOIL. Although available data on the question are meager at the present time there is evidence that moderate quantities of DDT and benzene hexachloride in the soil affect the growth of some plants. Benzene hexachloride at relatively low dosages gives excellent control of wireworm,.white grubs, and garden centipede without plant injury but it is possible that odor or taste may be absorbed by the plant. It is important t h a t the extent of these undesirable reactions be established in the near future so that valuable farm land will not be thrown out of production from the misuse of insecticides. THE NEED FOR RESEARCH
As more powerful insecticides are developed, more thorough research must be performed on all factors involved in the use of the chemicals. The problem is becoming complicated and the entomologist must have assistance from the chemist, the toxicologist, the plant physiologist, and the insect physiologist. If chemi cals, such as the new organic insecticides, are used over long periods of time and will kill insects when applied in minute quantities, precise use must be made of them. Before a chemical is recommended for commercial use i t should be determined that i t not only control the insect, but, that i t will not injure the crop to which it is applied, that i t will not leave a poisonous residue either on the crop or in the soil, that i t will be safe in the hands of the operator, and that i t will not upset the natural balance between the pest under control and its natural enemies: T o accomplish this specialists need the support and cooperation of each other. ECONOMIC VALUE OF INSECTICIDES
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The current market for agricultural products adds importance to the factors of yield and quality of crops to the growers. One way to obtain greater crop yields and better quality is through more efficient pest control. Losses to growing crops caused by insects were estimated ( 1 )
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in 1939 to average approximately 10 to 15y0 of all crops. However, the advent of the new synthetic organic insecticides caused entomologists to question the estimate on insect destruction. Before DDT was used commercially on potatoes, entomologists and farmers were of the opinion that Bordeaux mixture and calcium arsenate combinations gave good protection. against the hordes of insects attacking that crop. But the use of DDT has given such remarkable yield increases that the damage estimates seem far from the facts. The author has observed similar results with sweet corn. Rotenone and fixed nicotine have been used successfully on a commercial basis against the European corn borer for several years. More recently corn yields from plots treated with Ryania speciosa and synthetic organic insecticides have been remarkable. The difference in yield and quality cannot be entirely accounted for by the increased efficiency of corn borer control. The most logical explanation is that the rotenone and nicotine insecticides are specific for the European corn borer whereas the newer materials control not only the European corn borer but several other species of insects which heretofore had been considered as minor pests. During the past few years a marked change has occurred in the types of insecticides used on deciduous fruits; at the same time there has been a definite change in the economic importance of the fruit pests. Before D D T was used i n New Jersey orchards, the codling moth was by far the most important apple pest; curculio, apple maggot, and European red mite were considered minor problems, and the red-banded leaf roller was hardly known as a n apple pest. DDT has been used against the codling moth very successfully for the past two years and the formerly minor pest problems have now become the major pest problems. The protection of seed crops from insect attack with the newer insecticides gives reason to believe t h a t i t may be profitable t o use insecticides on low income crops, such as hay and pasture. Preliminary studies indicate that alfalfa yields are increased 50% or more by one application of a n insecticide. Other examples can be cited, but the above will suffice to show t h a t early estimates of insect damage t o growing crops were extremely low. However, the damages vary with different crops. I n general, crops which require a long growing season are more severely damaged than short-season crops. While the demand continues on the American farmer for increased production for home consumption and for shipments t o hungry nations abroad he cannot afford t o take chances. This means increased consumption of insecticides and less reliance on cultural practices, natural factors, and biologjcal agents to obtain good yields. But insecticides will be used as a precautionary measure only as long as a profitable return on investment is obtained. The pessimistic outlook on the situation is t h a t there will soon be overproduction of agricultural products, and a resultant decline in the consumption of insecticides t o below the prewar level. The other viewpoint is, t h a t with expanded research in the chemical field, new uses for the known insecticides will be found and other insecticides will be discovered to control species of insects against which the present chemicals are ineffective. This over-all program will demand increased insecticide consumption although a reduction in the total acreage in agricultural crops may result. LITERATURE CITED (1)
Metclaf, C. L., and Flint, mi. P., “Destructive and Useful In. sects,” 2nd ed., New Yo;k, McGraw-Hill Book Co., 1939.
RECEIVEDNovember 22, 1947. Journal Series paper of the’New Jersey Agricultural Experiment Station, Dept. of Entomology, Rutgers University.
