Mechanisms of resistance to pyrethroid insecticides

In the 10 years or so since the photostable pyrethroid insecticides such as permethrin and fenvolerate were introduced, this family of compounds has become widely used to control agricultural pests, and finds increasing usage to control arthropods of medical and veterinary importance. The synthetic pyrethroids offer many advantages for veterinary and public health use, particularly their selectivity, high toxicity to insects, and relative lack of chronic effects. They are also inherently stable, and so have become widely used as residual sprays on house walls to control insects in the domestic environment. But as with other classes of insecticides such as organochlorines, organophosphotes and carbamates, resistance to pyrethroids is now increasingly reported. In this article, Tom Miller explains the principle mechanisms of resistance to pyrethroids, using the North American horn fly (Haematobia irritans) as an example now showing many common resistance traits.