Methoprene is a juvenile hormone (JH) analog which can be used as an insecticide that acts as a growth regulator. Methoprene is essentially nontoxic to humans when ingested or inhaled. It is used in drinking water cisterns to control mosquitoes which spread malaria.
Methoprene does not kill adult insects. Instead, it acts as a growth regulator, mimicking natural juvenile hormone of insects. Juvenile hormone must be absent for a pupa to molt to an adult, so methoprene treated larvae will be unable to successfully change from a pupa to the adult insect. This breaks the biological life cycle of the insect preventing recurring infestation. "Methoprene is used in the production of a number of foods including meat, milk, mushrooms, peanuts, rice and cereals. It also has several uses on domestic animals (pets) for controlling fleas. Methoprene is considered a biochemical pesticide because rather than controlling target pests through direct toxicity, methoprene interferes with an insect’s life cycle and prevents it from reaching maturity or reproducing. Methoprene is used most widely as the mosquito larvicide Altosid, which is an important measure in prevention of West Nile virus.
Phenothrin (85.7%) in combination with methoprene was a popular topical flea/tick therapy, though primarily directed at felines. Phenothrin kills adult fleas and ticks. However, the US EPA has made at least one manufacturer of these products (Hartz Mountain Corp., Seacaucus, New Jersey, USA), withdraw some products and include strong cautionary statements on others, warning of adverse reactions. Phenothrin was believed to be the cause of the adverse reactions.