Definition
An Insect Growth Regulator, or IGR, is a pest control product that doesn't kill insects outright the way a traditional insecticide does. Instead, it disrupts their biological development — interfering with molting, maturing into an adult, or reproducing — so the insect either never reaches adulthood, can't reproduce successfully, or dies during a failed molt. Because IGRs target processes specific to insect development, they're generally considered very low-toxicity to people and pets.
IGRs are typically used alongside an adulticide (a product that kills adult insects directly) rather than by themselves, since an IGR alone won't quickly reduce a visible adult population — its strength is breaking the reproductive cycle so the population can't rebound. A pest control company treating a flea infestation, for example, might apply an adulticide to kill adult fleas immediately while also applying an IGR to prevent flea eggs and larvae in carpets and upholstery from ever developing into biting adults, which is critical since immature fleas can make up the majority of an infestation. The same combined approach is common in cockroach programs, where an IGR is used to suppress the population's ability to reproduce over the following weeks and months. Because of this delayed, cycle-breaking effect, IGRs are considered a long-term population control tool rather than a fast fix, and they're most effective as part of an ongoing treatment plan rather than a single visit.