Insecticide: A chemical used specifically to kill or control the growth of insects. Certain insecticides have been banned because of their adverse effects on animals or humans. Dursban (chlorpyrifos) is one that has been banned. Dursban causes weakness, vomiting, diarrhea and other ill effects in children. Dursban was in hundreds of products including some of Raid sprays, Hartz yard and kennel flea spray, and Black Flag liquid roach and ant killer.