insecticides

The Columbia Encyclopedia, 6th ed.

insecticides

insecticides, chemical, biological, or other agents used to destroy insect pests; the term commonly refers to chemical agents only.

Chemical Insecticides

The modern history of chemical insecticides in the United States dates from 1867, when Paris green proved effective against the Colorado potato beetle. Within a decade Paris green and kerosene oil emulsion were being employed against a variety of chewing and sucking insects. In the early part of the 20th cent. fluorine compounds and plant-derived insecticides were developed. Except for plant derivatives such as nicotine, pyrethrin, and rotenone, early insecticides were almost all inorganic chemicals. The discovery in Europe in 1939 of the insecticidal value of DDT, a synthetic organic compound, led to the synthesis of thousands of organic molecules in a search for potent chemicals. Today several hundred chemical insecticidal agents are registered by the U.S. Environmental Protection Agency and licensed in more than 10,000 formulations. Promptly effective, easy to use, and readily available, chemicals have become the modern weapons of choice against insects, contributing to stable food and fiber productivity, to human and animal health, and to the comfort and quality of human life.

As early as the 1920s, insecticide use in the United States prompted concerns over residues in foodstuffs and calls for regulation. In the 1960s, with increasing worldwide interest in environmental protection, chemical insecticides became objects of scientific and popular protest. Critics charged that chemical insecticides were dangerous and self-defeating, provoking the development of resistance by target pests, sabotaging ecological systems, and poisoning people and other organisms as well as the environment. In response, governments have restricted or proscribed many of the most dangerous insecticides, including many chlorinated hydrocarbon standbys: DDT, benzene hexachloride, lindane, aldrin, dieldrin, chlordane, heptachlor, endrin, and toxaphene—all powerful, broad-spectrum contact and stomach poisons.

Chemists, meanwhile, have invented alternative insecticides that attack selectively instead of indiscriminately, and that break down into nontoxic substances in the environment. Organophosphates attack insect nervous systems, much like the chlorinated hydrocarbons, but are much quicker to break down into nontoxic substances. A large and versatile group, the organophosphates include parathion, with one of the highest mammalian toxicities, and Malathion, with one of the lowest. Carbamate insecticides, esters of carbanilic acid that kill insect larvae, nymphs, and adults on contact, have gained favor because they break down even more quickly than organophosphates and are less hazardous to humans. Among the carbamates is Sevin, or carbaryl, an N-methyl aromatic carbamate ester.

Alternatives: Biological Insecticides

The liabilities of chemical insecticides have encouraged interest in biological controls, which turn natural processes and mechanisms against pest insects and have few if any harmful side effects. Biological controls include using predators, parasites, and pathogens to kill target insects without harming other organisms. In another strategy, huge numbers of sterilized male insects are released to compete with fertile males for mates, diminishing the population of the next generation. Interest is growing in the use of synthetic insect hormones to disrupt pests' vital processes, such as growth; and synthetic pheromones, powerful insect sex attractants, to monitor pest populations, sabotage pest reproduction, and lure pests into traps. In practice, however, some of the environmentally attractive features of biological insecticides—their inherently slow and selective activity, their strict management requirements—can make them economically unattractive to farmers. Increasingly, therefore, biological and chemical methods are coordinated in Integrated Pest Management programs.

Bibliography

See R. Carson, Silent Spring (1962); A. Mallis, Handbook of Pest Control (7th ed. 1990); G. J. Marco et al., ed., Regulation of Agrochemicals (1991); R. L. Metcalf, Destructive and Useful Insects: Their Habits and Control (5th ed. 1992).

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