Insecticide is a substance or mixture of substances used to kill insects. Insecticides are used in agriculture, forestry, industry, medicine, and households. The use of insecticides is regulated by law in many countries.
Insecticides are classified in two major groups: those that act on the nervous system and those that affect other body systems. Nervous system insecticides include organophosphates, carbamates, and pyrethroids. These insecticides work by interfering with the transmission of nerve impulses in insects. Insects that are killed by these insecticides usually die within minutes or hours after exposure. Other body system insecticides include botanicals (such as nicotine), chlorinated hydrocarbons (such as DDT), and growth regulators (such as methoprene). These insecticides work by disrupting one or more bodily processes in insects. For example, botanicals may interfere with an insect’s ability to digest food; chlorinated hydrocarbons may prevent an insect from being able to breathe; and growth regulators may disrupt an insect’s molting process (thus preventing it from reaching maturity). Insects that are killed by these types of pesticides typically take longer to die than those killed by nervous system pesticides – often days or weeks.
The first modern insecticide was arsenic acid, which was used in 1675 to control lice on humans. Arsenic-based compounds were also used to treat plant diseases such as downy mildew and black spot until the early 1900s when safer alternatives were developed. In the late 1800s, derris root powder and pyrethrum flower extracts were among the first natural products used as general purpose household and garden insecticides. Derris root contains rotenone, which is toxic to fish but has low toxicity for mammals; pyrethrum flowers contain several different chemicals – including pyrethrins – that have low toxicity for mammals but are effective against a wide range of flying and crawling insects. Pyrethrin-based products are still widely available today for use in homes, gardens, and petspaces