Insecticides are materials that kill, repel or regulate the growth of insects. They are wilfully used against those insects that are considered pest insects, although often they may kill beneficial non-target insects.
Often miticides (or acaricides) are included in the insecticid category. Insecticides may include substances developed to target life stages of insects or mites, thus may be referred to as adulticides, larvacides, or ovicides. Biological insecticides may be toxins produced by cultured organisms or they may be microscopic organisms themselves.
Some insects are regarded as pests because they compete with humans for food supplies, make foods unsightly and unappealing, vector diseases, damage wooden structures, or subject humans to irritating stings or bites. Insect larvae may damage crop plants or harvested food, and so are the bane of farmers and gardeners. Insecticides are often used in agricultural, to control pest insects. They are also used for public health; to control mosquitoes, fleas and other disease carrying insects.
Using insecticides may have unwanted secondary consequences. Insecticides may be toxic or detrimental to non-target organisms such as humans, fish and wildlife, and beneficial insects such as pollinators. Ground and surface waters may be polluted by insecticide runoff. Insecticides may kill or disrupt biologogical control agents, to the point of sometimes creating a backlash of explosive population growth of a pest insect.
Best practices in modern insecticide use is to attempt to reduce insecticide usage through better understanding of pest insect life cycles, natural control agents, and acceptance of a predetermined level of damage. This field is called "Integrated Pest Management" (IPM). A farmer who may have sprayed an orchard on a regular schedule 7 or 8 times during the growing season, may be able to reduce that schedule by half or more, according to the monitoring of actual pest levels by an IPM advisor.