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pesticide,biological, physical, or chemical agent used to kill plants or animals that are harmful to people; in practice, the term pesticide is often applied only to chemical agents. Various pesticides are known as insecticidesinsecticides,
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
..... Click the link for more information. , nematicides, fungicidesfungicide
, any substance used to destroy fungi. Some fungi are extremely damaging to crops (see diseases of plants), and others cause diseases in humans and other animals (see fungal infection).
..... Click the link for more information. , herbicidesherbicide
, chemical compound that kills plants or inhibits their normal growth. A herbicide in a particular formulation and application can be described as selective or nonselective.
..... Click the link for more information. , and rodenticides, i.e., agents primarily effective against insects, nematodes (or roundworms), fungi, weeds, and rodents, respectively.
Pesticides can be derived from plants (e.g., pyrethrin, neem) or minerals, or they can be chemically manufactured (e.g., DDT, 2,4-D). Natural predators and other biological methods are also used. Among the biological agents, parasites and predators feed on pests, pathogens sicken them, and pheromonespheromones,
any of a variety of substances, secreted by many animal species, that alter the behavior of individuals of the same species. Sex attractant pheromones, secreted by a male or female to attract the opposite sex, are widespread among insects.
..... Click the link for more information. interfere with insect mating. There are also genetically engineered pesticides, such as the toxin-producing Bacillus thuringiensis strain used against moth larvae.
Chemical pesticides are usually contact, stomach, or fumigant poisons. Contact poisons may have immediate or delayed effects after physical contact with a pest. Fumigants, which may initially have the form of a solid, liquid, or gas, kill pests while in a gaseous state.
Some insecticides and fungicides are systemic, i.e., they are translocated by a plant from the area of application to other plant parts, where they affect only pests that feed on the crop. Nonselective pesticides can affect both the targeted pest and other organisms; selective pesticides affect only the target pest. Persistent pesticides are those that remain in the environment for a long time.
Since the publication of Rachel CarsonCarson, Rachel Louise,
1907–64, American writer and marine biologist, b. Springdale, Pa., M.A. Johns Hopkins, 1932. Her well-known books on sea life—Under the Sea Wind (1941), The Sea around Us (1951), and The Edge of the Sea
..... Click the link for more information. 's Silent Spring in the 1960s, there has been concern regarding the effects of chemical pesticides on humans and on the environment. In the environment, the biological concentration of chemical pesticides (the amount retained in an organism through direct contact or consumption of affected plants or animals) tends to increase the higher the animal is in the food chain. DDTDDT
or 2,2-bis(p-chlorophenyl)-1,1,1,-trichloroethane, chlorinated hydrocarbon compound used as an insecticide. First introduced during the 1940s, it killed insects that spread disease and fed on crops, and Swiss scientist Paul Müller was awarded the 1948 Nobel Prize
..... Click the link for more information. , for example, severely reduced the rate of reproduction in many fish and birds.
Chemical pesticides now undergo exhaustive and expensive trials prior to government registration and release. The carcinogenicity of some pesticide components, however, is a vigorously debated topic. Government testing often uses massive amounts of such substances on laboratory animals, creating what some critics feel is an exaggerated assessment of their danger. Humans are heavily exposed to pesticides usually as a result of acute exposure, such as accidental inhalation, on the job.
Potential dangers from pesticide use must be weighed against improved crop quality and yield and greatly improved human health around the world, as well as the availability of disease-preventing fresh fruits and vegetables that the use of pesticides has made possible. Nevertheless, many consumers are concerned about the effects of pesticide residues in foods, especially for infants, whose systems may not be able to convert toxic chemicals into harmless substances as readily as adult systems can. In addition, concerns have been raised for farm workers in developing countries that lack the protective safeguards required in the United States; their health is threatened by the continued use of pesticides that are known health hazards. Efforts are being made to reduce chemical pesticide use in favor of Integrated Pest ManagementIntegrated Pest Management
(IPM), planned program that coordinates economically and environmentally acceptable methods of pest control with the judicious and minimal use of toxic pesticides.
..... Click the link for more information. (IPM), biological controls, and plant breeding for inherent pest resistance.
See R. Carson, Silent Spring (1962); P. Hurst et al., The Pesticides Handbook (1991); G. J. Marco et al., ed., Regulation of Agrochemicals (1991).