Insecticides are chemical substances used to destroy or control insect populations that could otherwise do billions of dollars in damage annually. Although the primary use of insecticides is in agriculture and animal husbandry, insecticides also help to control the spread of insect-borne diseases and to protect buildings, households, and products such as clothing and books. Historically, many kinds of insecticides have been developed, as no single poison is effective against all insect pests--indeed, most insecticides do not even remain effective against a single pest indefinitely. Insecticides can be broadly classified, based on their chemical structure, as inorganic or organic. The main ingredient of inorganic insecticides is of mineral origin, such as arsenic. Organic insecticides, whether derived from plants or made synthetically, consist of carbon in combination with one or more elements such as hydrogen, oxygen, sulfur, nitrogen, phosphorus, chlorine, or bromine. The toxicity of inorganic insecticides depends on...