Chapter 10: Natural Selection in the Field: Insecticide Resistance, Economic Entomology, and the Evolutionary Synthesis, 1914-1951

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In his 1937 book, Genetics and the Origin of Species, Theodosius Dobzhansky cited the emergence of insect populations that were resistant to chemical insecticides as "probably the best proof of the effectiveness of natural selection yet obtained" (Dobzhansky, 1937, p. 161). Dobzhansky learned of insect resistance first-hand from Henry J. Quayle, an economic entomologist and director of the Citrus Experiment Station in Riverside, California (Perkins, 1982, p. 65). Although by the mid-1930s, there were more than two dozen scientific articles published on insecticide resistance, Dobzhansky simply noted that Quayle "permits me to quote the following data from his manuscript" describing several species of insect pests, known collectively as scales, found in the citrus groves of southern California that no longer could be controlled by the standard chemical treatment of hydrocyanic gas fumigation. Dobzhansky further noted that "careful laboratory experiments have established beyond a reasonable doubt that the difference between the cyanide-resistant and the non-resistant strains is a real one," by which he meant that the cause was due to genetic variation in the insect populations (Dobzhansky, 1937, p. 161).

The examples of insect resistance found in natural populations of citrus scale in southern California provided a key piece of evidence in the formulation of Dobzhansky's "synthetic" theory of evolution. In the subsequent editions of Genetics and the Origin of Species published in 1941 and 1951, he gready expanded the section on historical changes of natural populations in which he discussed insect resistance, eliminating some of the outdated references to industrial melanism and crab body size that formed the bulk of his evidence for selection in the 1937 edition. He also included newer field and laboratory stuthes on resistance to insecticides, as well as the related phenomena of phage-resistance in bacteria.

Quayle and his group at the Citrus Experiment Station were not the first to study insect resistance to insecticides. In 1897, an entomologist from the New Jersey Agricultural Experiment Station noted the appearance of insect strains in Colorado and the eastern United States that no longer responded to standard treatment by kerosene spraying (Smith, 1897). In 1914, Axel L. Melander, an economic entomologist from Washington state described difficulties controlling the San Jose scale, a common apple orchard pest, dating back to 1908 (Melander, 1914). By the early 1940s, field researchers had identified about ten agricultural pests and laboratory strains that were capable of withstanding exposures to insecticides diat had previously been highly effective in killing these same species (Quayle, 1943). All of these cases involved resistance to inorganic insecticides such as those based on lead, arsenic, cyanide, and other toxic compounds diat had been in use since the nineteendi century. In addition, each of these early cases of insect resistance was a relatively local occurrence.

The phenomenon of insect resistance to insecticides achieved international scope in the mid- 1940s following the introduction and widespread use of DDT and other organic insecticides diat transformed insect resistance to a global agricultural and public healdi dilemma (Ceccatti, 2004a; Simon, 1999). By the early 1950s, there were more than two dozen resistant insect species - from houseflies and mosquitoes to granary weevils and bedbugs (Babers & Pratt, 1951). With the widespread application of DDT and other synthetic organic insecticides following the Second World War, insecticide resistance became not only a concern for agriculture but also a worry for global public health and even the military. At a 1951 conference convened by the U.S. Army Medical Research and Development Board, A. D. Ness, the Assistant Chief of the U.S. Public Healdi Service, noted diat "insecticide resistance is not a new problem to the agricultural entomologist, but to the medical entomologist it is a relatively new problem. …


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