Methoprene is referred to as an insect growth regulator because it interferes with the maturation stages through which an insect goes: from egg, larvae, and pupa, to adult.
Methoprene is a chemical that interferes with the development of insects, and some related arthropods. There are a number of similar chemicals that act this way and they are all called insect growth regulators (IGRs) because they stop normal insect growth and development. So, for example, if a larval flea (right) is exposed to methoprene it will not complete development to an adult flea and will eventually die. Manufacturers often refer to this as "breaking the flea's life cycle".
Growth regulators make it impossible for insects to mature to the adult stage of development.
Methoprene is considered a biochemical pesticide because rather than controlling target pests through direct toxicity, it interferes with the insects' life cycle and prevents them from reaching maturity or reproducing