Entomologists’ development of a technique to poison the cotton boll weevil led to intensified and widespread use of insecticides and diminished support for cultural and biological controls of insect pests.
The use of chemical insecticides in the United States intensified during the 1920’s following the development of a technique to poison the cotton boll weevil, one of the nation’s worst agricultural pests. Insecticide use had become established in the nineteenth century, when exotic pest insects arrived on steamers with European immigrants and on cargo ships.
As early as 1868, an unknown farmer discovered that Paris green (a brightly colored dye often used to paint window shutters) could kill the Colorado potato beetle. The active toxic ingredient in Paris green was arsenic, a poison also employed in insecticides developed later, such as London purple and lead arsenate. In a letter to the editor of the Galena Gazette on May 28, 1869, a Wisconsin farmer informed Illinois potato growers that an early-morning dusting of Paris green mixed with flour would kill beetle larvae. This advice was repeated in the July issue of the American Entomologist, and the practice of using Paris green on the potato beetle rapidly gained acceptance. In the 1870’s, Paris green was found to be effective against other pests as well, and it soon became a standard insecticide for the American farmer.
The nation’s agricultural industry had a serious need for insect control. In 1870, for example, journalist Horace Greeley estimated that the average annual loss to farmers from insect damage exceeded $100 million. Assisted by the Division of Entomology in the U.S. Department of Agriculture (USDA), farmers found themselves with three basic strategies for fighting pest insects: insecticides, biological controls, and cultural controls. By the 1920’s, insecticides had emerged as the principal means of insect control, in large part because of the Division of Entomology’s experience with three pests: the cottony-cushion scale, the gypsy moth, and the cotton boll weevil.
The cottony-cushion scale had been accidentally imported from Australia or New Zealand in the 1870’s. Arsenicals had limited effect on the pest, so there was little to prevent its rapid spread through the orange and lemon groves of California in the 1880’s. Charles Valentine Riley, first chief of the USDA’s Division of Entomology, noted that the cottony-cushion scale posed a significant problem in New Zealand. He concluded that the species was native to Australia and had been kept in check there by natural enemies, so it was neither abundant nor injurious.
Riley sent his assistant, Albert Koebele, to Australia to search for the scale’s natural predators. Koebele returned in 1889 with a small beetle that preyed on the scale. Known as the Australian ladybird, or vedalia beetle, the new predator became so effective that the scale was brought under control in the first season after the beetle’s release. The results of this experiment aroused great enthusiasm among farmers and entomologists, many of whom saw biological control as the solution to the war on insects and boldly predicted that spraying insecticides would no longer be necessary. By 1920, however, this confidence in biological control had been replaced largely by a renewed faith in insecticides.
The gypsy moth
The caterpillars created a nightmare for Medford, defoliating trees, covering sidewalks and fences, and invading food and bedding inside houses. They were found to be resistant to Paris green and able to consume nearly ten times the amount of arsenic required to kill caterpillars of other species. Increasing the proportion of arsenic merely burned the foliage. Relief came in 1892 when the chemist F. C. Moulton found that lead arsenate could kill the caterpillar without as much injury to foliage as that produced by Paris green. Lead arsenate proved effective on the moth and on other insects; in the early 1900’s, it became the most popular insecticide until it was replaced by dichloro-diphenyl-trichloroethane (DDT) in the 1940’s.
After the California experience with the vedalia beetle, however, many believed that ultimate control of the gypsy moth would come when a suitable insect predator was found. Financed by state and federal funds, Howard traveled to Europe to search for natural enemies of the moth. Progress was slow. In Europe, the gypsy moth was kept in check by fifty parasites, and control in the United States might require importing all of them. Finally, in 1930, Howard concluded that biological control was far more complicated than entomologists had believed twenty years earlier and that the successful experience with the vedalia beetle had been an exceptional case. Although some control was eventually achieved through the introduction of natural enemies, the gypsy moth generally was kept in check through the use of lead arsenate.
The cotton boll weevil problem furnishes an example of why cultural insect controls largely failed in American agriculture. The USDA was alerted to the boll weevil problem in 1894, when it received word from Corpus Christi, Texas, that a peculiar weevil had destroyed much of the “top crop” of cotton (a late harvest possible whenever the first frost arrives late). Local farmers found that ordinary poisons had no effect on the pest. Howard immediately dispatched entomologist C. H. Tyler Townsend to investigate the infestation. Townsend found extensive crop damage and recommended cultural control measures, such as burning or flooding the stalks after the main harvest to eliminate the weevil’s food source prior to hibernation and the establishment of a fifty-mile-wide noncotton zone along the Texas international border to prevent further in-migration of the insect from Mexico.
By the end of the next year, the boll weevil had spread well into Texas. Strong opposition from constituent farmers forced state legislators to decide against a noncotton zone on the Mexican border. Farmers also rejected other cultural control measures recommended by the Division of Entomology for socioeconomic reasons. Destruction of the crop after the main harvest, for example, would deprive farmers of the chance for a top crop and thus posed an immediate economic cost with no guarantee of a more profitable harvest the next year. Furthermore, if neighboring farmers did not employ the same measures, the weevils would continue to thrive in nearby fields.
It was known that weevils fed from the cotton squares and bolls through deep punctures, thus avoiding poisons, which would remain on the surface tissue of the plant. Nevertheless, Texas farmers used an estimated twenty-five boxcarloads of Paris green during a three-month period in 1904 in futile attempts to destroy the boll weevil. A breakthrough finally occurred in 1914 when bureau entomologist Bert Raymond Coad saw the possibility of poisoning the insect by means of the dew on the leaves of cotton plants. Over the next three years, he experimented with this idea on cotton plantations in Louisiana, Arkansas, and Mississippi. The results of these tests were highly encouraging.
Numerous large-scale experiments were conducted in 1917 and 1918, and the success of these tests led to USDA guidelines on poisoning the boll weevil. Coad had found calcium arsenate to be more poisonous to the insect than other arsenicals. His experimental work also verified his theory that the weevil’s habit of drinking from water on the plant’s surface could be used to introduce the poison. He recommended that farmers dust their crops at night, when the plants were especially moist from the dew. The combination of the new insecticide and the approach of poisoning weevils through their drinking rather than their feeding habits proved effective in controlling cotton damage caused by the pest. An insecticide again had provided the most convenient form of insect pest control.
During the 1920’s, American farmers became increasingly reliant on the utility offered by insecticides. No other method, it seemed, would stop insects as effectively as chemicals. New techniques were developed to increase the ease and efficiency of insecticide application. In 1922, for example, Coad demonstrated the possibility of dusting cotton crops from the air; by 1927, one aerial crop-dusting company had contracts to treat one-half million acres of cotton.
The manufacture of insecticides developed into a large industry that provided further encouragement and support to farmers inclined to dust and spray. Prior to 1918, for example, only one manufacturer was making calcium arsenate, with a total annual production of about 50,000 pounds. Two years later, twenty-five manufacturers were making it, and their combined output was more than 10 million pounds per year. The sharp increase in production reflected the new demand for calcium arsenate as an insecticide for the boll weevil. From the time of Coad’s discovery in 1917, production continued to grow until calcium arsenate became the second most common arsenical insecticide in use, next to lead arsenate. The annual production of lead arsenate increased from 11.5 million pounds in 1919 to more than 37 million pounds in 1931. Annual production of calcium arsenate by 1931 had climbed to more than 26 million pounds.
In 1924, A. G. Ruggles, president of the American Association of Economic Entomologists, complained that young entomologists were not dedicating enough time to the study of insects; instead, they were experimenting with insecticides to control pests even before they had thorough understanding of the life cycles of those insects. Publicly funded economic entomologists were under pressure to make recommendations on control methods they knew would produce immediate results, and chemical insecticides had become the most efficient weapons in the war on insects.
Some commentators raised public health concerns about chemical residues on food shortly after Paris green first gained popularity as an insecticide, but the U.S. government did not set tolerance levels for arsenic and lead residues until the 1920’s and 1930’s. These levels, set by the USDA, were based more on what the department believed industry could achieve through washing than on information about safe amounts of exposure. With few exceptions, government officials were looking for evidence of acute poisoning rather than chronic health effects from long-term exposure to spray residues. The potential for cumulative impacts from lifetime ingestion of these chemicals did not become an important issue for public debate until after the publication of Rachel Carson’s Silent Spring in 1962.
The popularity of arsenical insecticides prepared the way for the rapid, almost indiscriminate, acceptance of DDT when it became available after World War II. By 1945, insecticides were already well established in the social and technological framework of American agriculture. It was not until the 1960’s, however, that the general public became aware of indirect health effects resulting from insecticides that washed off the land into streams and lakes, poisoning fish, wildlife, and humans.
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Berenbaum, May R. Bugs in the System: Insects and Their Impact on Human Affairs. Boston: Addison-Wesley, 1995. Survey of the life and evolution of insects around the world, with emphasis on how insects have affected and continue to affect human beings and their societies. Chapter 9 is devoted to humans’ development of ways to eradicate insects. Includes index. -
Dunlap, Thomas R. DDT: Scientists, Citizens, and Public Policy. Princeton, N.J.: Princeton University Press, 1981. Excellent, highly readable source for the DDT story in historical context. Focuses on the interaction of science and politics in the DDT controversy, but also provides background on insecticides, entomology, and public health prior to DDT. Includes bibliography and index. -
Howard, Leland Ossian. A History of Applied Entomology (Somewhat Anecdotal). Washington, D.C.: Smithsonian Institution, 1930. A valuable resource for students of the history of entomology. Highly personal account ranges from biographical sketches of important figures such as Riley to the use of beneficial predatory insects in thirty-two countries. A useful synthesis of the early development of economic entomology by a man with more than fifty years of government service. Includes illustrations and index. -
Perkins, John H. Insects, Experts, and the Insecticide Crisis: The Quest for New Pest Management Strategies. New York: Plenum, 1982. A useful source for students interested in the history of science and technology as it applies to entomology and insecticides. Traces the movement toward integrated pest management strategies and the role of the entomological expert in American agriculture. Includes figures and index. -
Rudd, Robert L. Pesticides and the Living Landscape. Madison: University of Wisconsin Press, 1964. Includes some historical background, but primarily addresses the environmental hazards of chemical pest control. Describes various kinds of pesticides and summarizes their regulation and economics. Argues for the diversification of pest control measures with limited use of chemicals. Includes tables, bibliography, and index. -
Steinberg, Ted. Down to Earth: Nature’s Role in American History. New York: Oxford University Press, 2002. An examination by an environmental historian of how geography, plants, animals, and natural resources have shaped the economic, political, and cultural institutions of the United States. Includes brief discussion of the impact of agricultural use of pesticides. -
Whorton, James. Before “Silent Spring”: Pesticides and Public Health in Pre-DDT America. Princeton, N.J.: Princeton University Press, 1974. A good source for the early history of insecticide use, recognition of public health problems from spray residues, and the federal regulation of insecticides as these health problems became increasingly apparent. Explains the background of the DDT controversy thoroughly and provides examples. Includes index.
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