Allethrin is a nonsystemic insecticide that is used almost exclusively in homes and gardens for control of flies and mosquitoes, and in combination with other pesticides to control flying or crawling insects. Another structural form, the d-trans- isomer of allethrin, is more toxic to insects and is used to control parasites living within animal systems. It is available as mosquito coils, mats, oil formulations, and as an aerosol spray. Allethrin is a pyrethroid, a synthetic compound that duplicates the activity of the pyrethrin plant. It has stomach and respiratory action and paralyzes insects before killing them. Unless stated otherwise, information in this profile refers to unpurified allethrin.