insecticides: Chemical Insecticides

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.

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