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Insecticide, any substance toxic to insects and used to control them in situations where they cause economic damage or endanger the health of humans and their domestic animals. There are 3 main types: stomach insecticides, which are ingested by the insects with their food; contact insecticides, which penetrate the cuticle (exterior covering); and fumigant insecticides, which are inhaled. Stomach insecticides are often used to control chewing insects like caterpillars and sucking insects like aphids. They may be applied to a plant prior to attack and remain active in or on the plant for a considerable time. They must be used with considerable caution on food plants or animal forage. Examples include arsenic compounds, which remain on the leaf, and organic compounds, which are absorbed by the plant and transported to all its parts (systemic insecticides). Contact insecticides include the plant products nicotine, derris, and pyre-thrum, which are quickly broken down, and synthetic compounds such as DDT (and other chlorinated hydrocarbons), organophosphates (malathion, parathion), and carbamates. Polychlorinated biphenyls (PCBs) are added to some insecticides to increase their effectiveness and persistence. Highly persistent insecticides may be concentrated in food chains and exert harmful effects on other animals such as birds and fish.

See also: Insect.

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21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Inert gas to Jaruzelski, Wojciech