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Insect growth regulators (IGRs)

Insect growth regulators are insecticides that mimic hormones in young insects. They rarely kill adults; instead they stop eggs from hatching and young insects from maturing, so a population dies out over time.[1]

The short answer

  • Expect to keep seeing adult insects for a while after an IGR treatment: adults usually survive and remain a nuisance until they die naturally.[1]
  • Using more product will not make an IGR work better; follow the label's mixing directions.[1]
  • Many IGR products are combined with an insecticide that kills adults. IGRs are generally low in toxicity to humans.[1]
  • IGRs can harm helpful insects such as bees, so treat only the problem areas.[1]
  • There are two broad kinds. Juvenile hormone mimics (methoprene, hydroprene, pyriproxyfen and others) keep young insects from maturing; chitin synthesis inhibitors (such as diflubenzuron, novaluron and the termite-bait ingredients hexaflumuron and noviflumuron) interfere with chitin, the material insects use to build their hard outer shell. Both usually act slowly.[6][7]

How IGRs work

IGRs act on insect hormones that people don't have. Treated eggs may never hatch, larvae may be unable to develop into adults, and some adults become sterile.[1]

Methoprene acts like an insect hormone and can prevent normal molting, egg-laying, egg-hatching and development from the immature to the adult stage. It was first registered in the United States in 1975.[5]

Pyriproxyfen, registered since 1995, mimics a natural insect hormone and affects mostly young insects and eggs, including fleas, cockroaches, ticks, ants, carpet beetles and mosquitoes.[2]

IRAC classifies methoprene as a Group 7A juvenile hormone mimic.[6]

Insect growth depends on the balance between two hormones, juvenile hormone and ecdysone, the molting hormone. IRAC says growth regulators either mimic one of these hormones or interfere with how the insect's cuticle is formed, and that they generally act slowly to moderately slowly.[6]

EPA puts it this way: some growth regulators alter the production of chitin, the material insects use to build their hard outer shell, and others alter development into adulthood. Some force an insect to develop too quickly, while others stop development.[7]

The main types and active ingredients

Product labels and pesticide charts often use IRAC's mode-of-action group numbers. Rotating between groups with different modes of action is one way to slow resistance, so the number on the label is worth noting.[6][7]

  • Group 7, juvenile hormone mimics: hydroprene, kinoprene and methoprene (7A), fenoxycarb (7B) and pyriproxyfen (7C). Applied to the stage before metamorphosis, they disrupt and prevent it.[6]
  • Group 15, chitin synthesis inhibitors (benzoylureas): includes diflubenzuron, hexaflumuron, lufenuron, novaluron and noviflumuron. They block the enzyme that builds chitin.[6][7]
  • Group 16, buprofezin: also blocks chitin formation, in ways not fully worked out, in a number of insects including whiteflies.[6]
  • Group 17, cyromazine: disrupts molting in flies; its exact mode of action isn't fully defined.[6]
  • Group 18, ecdysone agonists: methoxyfenozide, tebufenozide and related compounds mimic the molting hormone and trigger a molt too early.[6]

Which pests they're used on

NPIC names fleas, cockroaches and mosquitoes as pests IGRs can control. NPIC says pyriproxyfen also affects ticks, ants and carpet beetles, and that methoprene is used against fleas, flies, moths and beetles.[1][2][5]

  • Mosquitoes: IGR larvicides keep larvae from completing the immature stage, so they never become adults; CDC gives methoprene and pyriproxyfen as examples. UC IPM describes methoprene as a mosquito hormone mimic applied to standing water to stop adults emerging.[9][10]
  • Ants: fire ant baits with an IGR (methoprene, pyriproxyfen or fenoxycarb) are slower than fast-acting baits but last longer. Texas A&M says they work in 1 to 2 months when applied in spring and 6 months when applied in fall; UC IPM gives 4 to 6 weeks for maximum effect.[13][14]
  • Pharaoh ants: in a USDA-ARS study, a pyriproxyfen bait spread to all nest sites; brood fell 95% by week 3 and workers declined gradually by 73% after 8 weeks. Because the IGR didn't kill workers quickly, more of them survived to carry bait to every colony.[15]
  • Drain flies and other small flies: most insecticides aren't labeled for drains, but S-hydroprene can be used there as a spray or foam. It doesn't kill adult flies; it keeps larvae from completing development.[16]
  • Scale insects: pyriproxyfen and buprofezin keep immature nymphs from developing into functioning adults, and University of Minnesota calls them effective low-impact options. They're available only to licensed applicators.[17]
  • Grasshoppers and Mormon crickets on western rangeland: USDA APHIS uses diflubenzuron, a chitin inhibitor, for most of its treatments, aimed at young grasshoppers before they reach adulthood.[18]
  • Bed bugs: EPA lists insect growth regulators as one of the seven chemical classes registered for bed bug control.[7]
  • Stored food: methoprene is allowed on a wide variety of foods, including stored grains.[5]

Cockroaches

An IGR won't clear out the roaches you can see. Adults live on until they die naturally, so use one alongside bait rather than instead of it. In a Virginia Tech public-housing study, the IPM program combined vacuuming, baits and IGR devices.[1][12]

Purdue lab work on hydroprene found that exposed German cockroaches became sterile adults with twisted wings. Population declines began at about the time roughly 80% of adults had twisted wings, and the researchers proposed that level as a threshold for managing juvenoid treatments.[11]

Fleas

  • The most effective indoor flea sprays also contain the IGR methoprene or pyriproxyfen. Spray carpets, pet sleeping areas, carpet under furniture, baseboards and windowsills.[3]
  • Foggers don't give the coverage or long-term effect of direct sprays unless they contain methoprene or pyriproxyfen; sprays without an IGR often miss larvae at the base of carpet fibers.[3]
  • The spray doesn't kill pupae, so fleas keep emerging for about 2 weeks. Keep vacuuming and don't re-treat for at least several weeks.[3]
  • Outdoors, where a pet sleeps and flea numbers are high, those areas can be treated with a spray containing pyriproxyfen.[3]
  • Flea collars may contain methoprene or pyriproxyfen. The collar releases the IGR, which spreads through the pet's coat and affects eggs and female adult fleas; UC IPM notes very little has been published on how well collars work.[3]

Termite baits

The most effective subterranean termite baits use IGRs to suppress or destroy the whole colony. IGRs have very low toxicity to people and pets, but the most effective bait products are for professional use only.[4]

EPA lists diflubenzuron, hexaflumuron, lufenuron and noviflumuron as the most common active ingredients in termite baits. Hexaflumuron was the first active ingredient registered as a reduced-risk pesticide. All four are chitin synthesis inhibitors in IRAC's Group 15.[8][6]

How long they last outdoors, bees and water

Sunlight and microbes break methoprene down quickly. In soil about half is gone within 10 to 14 days, and in water half breaks down in 1 to 28 days depending on sunlight. Briquettes, pellets and granules release it slowly; full breakdown from a briquette has been reported to take up to 18 months.[5]

Pyriproxyfen also breaks down in sunlight and soil. NPIC gives a half-life of 6.8 to 16 days on sunlit soil and 3.7 to 21 days in sunlit water. It binds tightly to soil, so it isn't likely to reach groundwater, but spray drift and runoff can carry it into surface water.[2]

Bees: methoprene appears low in toxicity to adult bees, and pyriproxyfen is practically nontoxic to adult honey bees, but bee eggs and larvae are more sensitive to both. That's the reason to keep IGR sprays to the problem areas.[5][2][1]

Fish: pyriproxyfen is moderately to highly toxic to fish depending on the species, and methoprene is moderately toxic to some fish and can build up in fish tissue.[2][5]

Safety

  • Pyriproxyfen is considered low in toxicity for humans and other mammals; it can mildly irritate eyes.[2]
  • You can be exposed to pyriproxyfen by touching a treated pet; follow label instructions to limit exposure.[2]
  • Methoprene is very highly toxic to freshwater invertebrates and moderately toxic to some fish, so keep it out of water.[5]
  • Identify your insect first: some IGRs work better on certain insects than others.[1]
  • Methoprene can cause slight eye irritation and mild to moderate skin irritation. NPIC reports it is not expected to contribute to cancer, and EPA classifies pyriproxyfen as not likely to cause cancer in humans.[5][2]
  • Young children may be exposed more because they spend time near the floor and put their hands in their mouths after touching treated surfaces or pets. EPA found infants and children are not more sensitive to pyriproxyfen than adults.[2]
  • If someone is exposed, follow the first aid instructions on the label; for more treatment advice, call Poison Control at 800-222-1222. For questions about a pesticide, NPIC is at 800-858-7378.[2][5][1]

Common questions

Why am I still seeing fleas or roaches after an IGR treatment?
IGRs rarely kill adults, so the adults you see keep going until they die naturally. With fleas, pupae also survive the spray and new adults keep emerging for about 2 weeks.[1][3]
Does a stronger mix work faster?
No. Using more product won't make an IGR more effective; mix it the way the label says.[1]
How long does an IGR fire ant bait take?
Longer than fast-acting baits. UC IPM gives 4 to 6 weeks for maximum effect, and Texas A&M says 1 to 2 months after a spring application and 6 months after a fall one, with control that lasts longer.[14][13]
Are chitin inhibitors and hormone mimics the same thing?
No. Hormone mimics such as methoprene and pyriproxyfen copy juvenile hormone and stop insects maturing; chitin synthesis inhibitors such as diflubenzuron and novaluron block the enzyme that builds chitin, the material of the outer shell. Both are counted as growth regulators.[6][7]

Sources

  1. National Pesticide Information Center, “Insect Growth Regulators (IGRs).” npic.orst.edu/ingred/ptype/igr.html (accessed 2026-11-10)
  2. National Pesticide Information Center, “Pyriproxyfen General Fact Sheet.” npic.orst.edu/factsheets/pyriprogen.html (accessed 2026-11-10)
  3. University of California Statewide IPM Program, “Fleas (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/fleas/ (accessed 2026-11-10)
  4. University of California Statewide IPM Program, “Subterranean and Other Termites (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/subterranean-and-other-termites/ (accessed 2026-11-10)
  5. National Pesticide Information Center, “Methoprene General Fact Sheet.” npic.orst.edu/factsheets/methogen.html (accessed 2026-11-10)
  6. Insecticide Resistance Action Committee, “IRAC Mode of Action Classification Scheme, Version 11.5 (Feb. 2026).” irac-online.org/documents/moa-classification/ (accessed 2026-11-10)
  7. U.S. Environmental Protection Agency, “Pesticides to Control Bed Bugs.” www.epa.gov/bedbugs/pesticides-control-bed-bugs (accessed 2026-11-10)
  8. U.S. Environmental Protection Agency, “Termites: How to Identify and Control Them.” www.epa.gov/safepestcontrol/termites-how-identify-and-control-them (accessed 2026-11-10)
  9. Centers for Disease Control and Prevention, “Larvicides.” www.cdc.gov/mosquitoes/mosquito-control/larvicides.html (accessed 2026-11-10)
  10. University of California Statewide IPM Program, “Mosquitoes (Pest Notes, Home and Landscape).” ipm.ucanr.edu/home-and-landscape/mosquitoes/ (accessed 2026-11-10)
  11. Journal of Economic Entomology, abstract via PubMed, “Reid and Bennett 1994, Hydroprene effects on the dynamics of laboratory populations of the German cockroach.” pubmed.ncbi.nlm.nih.gov/7836613/ (accessed 2026-11-10)
  12. Journal of Economic Entomology, abstract via PubMed, “Miller and Meek 2004, Cost and efficacy comparison of integrated pest management strategies with monthly spray insecticide applications for German cockroach control in public housing.” pubmed.ncbi.nlm.nih.gov/15154482/ (accessed 2026-11-10)
  13. Texas A&M AgriLife Texas Imported Fire Ant Research and Management Project, “Control Methods.” fireant.tamu.edu/controlmethods/ (accessed 2026-11-10)
  14. University of California Statewide IPM Program, “Pest Notes: Red Imported Fire Ant, Publication 7487 (December 2013).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnredimportedfireant.pdf (accessed 2026-11-10)
  15. Journal of Economic Entomology, abstract via PubMed, “Oi DH, Vail KM, Williams DF. 2000. Bait distribution among multiple colonies of Pharaoh ants.” pubmed.ncbi.nlm.nih.gov/10985038/ (accessed 2026-11-10)
  16. Texas A&M AgriLife Extension Service, “Indoor Flies and Their Control.” agrilifeextension.tamu.edu/library/insects/indoor-flies-and-their-control/ (accessed 2026-11-10)
  17. University of Minnesota Extension, “Scale insects on Minnesota trees and shrubs.” extension.umn.edu/garden-and-home/yard-and-garden/yard-and-garden-insects/scale-insects (accessed 2026-11-10)
  18. USDA Animal and Plant Health Inspection Service, “FAQ: Grasshoppers and Mormon Crickets in Western States.” www.aphis.usda.gov/plant-pests-diseases/ghmc/grasshoppers-mormon-crickets-western-faqs (accessed 2026-11-10)

Updated 2026-11-10. Built from sourced records. Spot an error? Tell us.