Insect Growth Regulators (IGRs) are an underappreciated precision tool in the IPM toolbox — unlike traditional insecticides that directly poison pests, they precisely disrupt the unique developmental processes of insects.

IGRs are mainly divided into two major categories.

Juvenile hormone analogs (JHAs) mimic the action of the insect juvenile hormone — in normal development, a drop in juvenile hormone level is the critical signal for a larva to molt into the pupal or adult stage.

JHAs maintain a high level of juvenile hormone signal, preventing larvae from pupating or preventing pupae from emerging as adults, trapping the insect in the immature stage where it eventually dies; methoprene is a key example.

Chitin synthesis inhibitors (CSIs) inhibit the chitin synthase enzyme, preventing the insect from forming a new exoskeleton during molting — the nymph dies during the molt because it lacks a new chitin layer to support its body wall; hexaflumuron and chlorfluazuron are examples.

Advantages of IGRs: extremely low mammalian toxicity (mammals do not have chitin or juvenile hormone systems), and the rate at which pests develop resistance is generally slower.

Limitations: slow-acting — they do not kill existing adults; you must wait for the next generation to die during development, typically taking 2–6 weeks to see a population decline.

This is why IGRs and fast-acting adulticides are often used in combination — IGRs provide long-term population control, while adulticides provide immediate results.