Cyromazine, an insect growth regulator, affects larval and pupal cuticles in dipterans and some other insects. The mode of action of this aminotriazine is not known yet, though it has been shown not to inhibit the synthesis of chitin and cuticular proteins. Cyromazine may, however, act on some step(s) of sclerotization of the cuticle. Cyromazine is not a cholinesterase inhibitor. As an insect growth regulator, cyrozine exerts its toxic action by affecting the nervous system of the immature stages (larvae) of certain insects.