Allethrin is a first generation synthetic pyrethroid, which is similar in chemical composition to one of the components found in natural pyrethrin, Cinerin I. This insecticide functions in much the same way as natural pyrethrins by affecting nerve function in insects and is not a cholinesterase inhibitor. Although more stable to heat and light, its persistence in the environment is also limited lasting for at best a few days. Napa County Mosquito Abatement District uses Allethrin on a very limited basis as part of its yellowjacket control program.