Insecticides

Insecticides are an extremely diverse group of chemicals, plus additional formulations based on living microorganisms. The most important groups of insecticides are described below.

• Inorganic insecticides are compounds containing arsenic, copper, lead, or mercury. They are highly persistent in terrestrial environments, being slowly dispersed by leaching and erosion by wind and water. Inorganic insecticides are used much less than in the past, having been widely replaced by synthetic organics. Examples of insecticides include Paris green (a mixture of copper compounds), lead arsenate, and calcium arsenate.
• Natural organic insecticides are extracted from plants. They include nicotine extracted from tobacco (usually applied as nicotine sulphate), pyrethrum extracted from daisy-like plants, and rotenone from several tropical shrubs.
• Chlorinated hydrocarbons (or organochlorines) are synthetic insecticides, including DDT and its relatives DDD and methoxychlor, lindane, and cyclodienes such as chlordane, heptachlor, aldrin, and dieldrin. Residues of organochlorines are quite persistent in the environment, having a half-life of about 10 years in soil. They are virtually insoluble in water, but are highly soluble in fats and lipids. Their persistence and strongly lipophilic nature causes organochlorines to bio-concentrate and to further food-web magnify in high concentrations in species at the top of food webs.
• Organophosphate insecticides include fenitrothion, malathion, parathion, and phosphamidon. These are not very persistent in the environment, but most are extremely toxic to arthropods and also to non-target fish, birds, and mammals.
• Carbamate insecticides include aldicarb, aminocarb, carbaryl, and carbofuran. They have a moderate persistence in the environment, but are highly toxic to arthropods, and in some cases to vertebrates.
• Synthetic pyrethroids are analogues of natural pyrethrum, and include cypermethrin, deltamethrin, permethrin, synthetic pyrethrum and pyrethrins, and tetramethrin. They are highly toxic to invertebrates and fish, but are of variable toxicity to mammals and of low toxicity to birds.
• More minor groups of synthetic organic insecticides include the formamidines (e.g., amitraz, formetanate) and dinitrophenols (e.g., binapacryl, dinocap).
• Biological insecticides are formulations of microbes that are pathogenic to specific pests, and consequently have a relatively narrow spectrum of activity in ecosystems. An example is insecticides based on the bacterium Bacillus thuringiensis (or B.t.). There are also insecticides based on nuclear polyhedrosis virus (NPV) and insect hormones.