Awaiting expert review. This page covers safety or regulatory rules that change over time. It is kept out of search results until a qualified reviewer has checked it; the sources below are dated so you can verify each point.
Quick answer
An insect growth regulator (IGR) is an insecticide that disrupts how an insect develops, either by keeping young insects from maturing into breeding adults or by stopping them from building a new outer shell when they molt, rather than killing adults on contact.
Common examples are methoprene, pyriproxyfen and hydroprene for fleas, bed bugs and mosquitoes, and noviflumuron and hexaflumuron in termite baits.
Quick facts
The key facts about Insect Growth Regulator (IGR), with sources:
- Two main groups
- Juvenile hormone analogs and chitin synthesis inhibitors 1
- Hormone analog examples
- Methoprene, pyriproxyfen, hydroprene 1
- Chitin inhibitor examples
- Diflubenzuron, lufenuron; hexaflumuron and noviflumuron in termite baits 18
- Why low risk to mammals
- Mammals have no juvenile hormone system 1
- Methoprene, first registered
- 1975, later reclassified as a biochemical pesticide 5
- Kills adults?
- Hormone analogs do not kill insects directly 1
- Bed bug class
- IGRs are one of seven registered bed bug classes 7
Key takeaways
- An IGR attacks the next generation: young insects fail to grow up, or die when they try to shed their skin.
- Most IGRs do not kill the adults you can see, so they are usually paired with another product or method.
- They work best against pests that breed fast indoors, such as fleas, and in slow colony baits for termites.
- Mammals lack the hormone system IGRs target, which is why they are generally low in toxicity to people and pets.
- Low toxicity to people is not the same as harmless: methoprene is highly toxic to estuarine invertebrates, the EPA found.
What an IGR is
Most insecticides kill an insect fast by attacking its nerves, while an IGR interferes with growing up instead. A flea larva treated with an IGR never becomes a biting, egg-laying adult, and a termite fed an IGR bait dies the next time it tries to molt.
The Merck Veterinary Manual describes IGRs as products that target insect growth and development at an early stage, unlike most products that kill adults 1. It sorts them into two groups 1:
Juvenile hormone analogs copy a hormone that keeps insects young. Too much of it at the wrong time stops larvae from maturing into adults that can breed. Methoprene, pyriproxyfen and hydroprene are examples. They do not kill insects directly 1.
Chitin synthesis inhibitors block chitin, the material in an insect’s hard outer shell. Larvae molt without a proper shell and die. Diflubenzuron and lufenuron are examples 1. The termite bait ingredients hexaflumuron and noviflumuron also stop molting 89.
How IGRs work, step by step
The two groups act at different moments in an insect’s life.
- Exposure. A young insect eats, touches or absorbs the IGR, or an adult female carries it to her eggs. UC IPM notes that IGR flea collars spread through the pet’s coat and affect eggs and female adults 2.
- Hormone analogs: stuck young. The insect receives a “stay young” signal at the wrong time and cannot mature into a breeding adult 15.
- Chitin inhibitors: failed molt. The insect molts without a proper shell and dies 1.
- No new breeders. As young insects fail, the number of new adults drops over the following weeks.
- Adults age out. Existing adults are often untouched by hormone analogs 1, so another method usually removes them.
- EggSome IGRs reach eggs through treated females
- Larva or nymphHormone analogs keep it from maturing
- MoltChitin inhibitors cause a failed molt
- AdultUsually not killed by hormone analogs
- Next eggsFewer breeding adults means fewer eggs
- Back to step 1
IGRs act on the next generation. That is why they pair well with a method that removes adults. Source: [1] [2]
Types of IGRs and where they are used
| IGR | Group | Uses in the sources |
|---|---|---|
| Methoprene | Juvenile hormone analog 1 | Mosquitoes, flies, moths, beetles and fleas 5; flea products 2 |
| Pyriproxyfen | Juvenile hormone analog 1 | Flea control on pets 1; flea products 2 |
| Hydroprene | Juvenile hormone analog 1 | Bed bugs; may take many days to act 3 |
| Lufenuron | Chitin synthesis inhibitor 1 | Monthly pill or 6-month injection for pets; stops flea reproduction 2 |
| Diflubenzuron | Chitin synthesis inhibitor 1 | Termite bait ingredient 8 |
| Hexaflumuron, noviflumuron | Molt-blocking termite bait ingredients 9 | Termite bait stations 8 |
The EPA lists IGRs as one of the seven chemical classes registered for bed bugs 7. See how bait stations use them in termite baiting systems.
Example: how long an IGR termite bait took to eliminate colonies
A peer-reviewed field study baited 122 subterranean termite colonies with 0.5% noviflumuron, a molt-blocking IGR, and refilled the bait every three months 9. The authors compared their results with an earlier study that refilled monthly. The figures show how slowly, and how surely, an IGR bait works.
| Measure | Quarterly refills | Monthly refills (earlier study) |
|---|---|---|
| Mean days to colony elimination | 96 9 | 107 9 |
| Median days to colony elimination | 74 9 | 90 9 |
| Colonies eliminated in the first quarter | 63% 9 | Not reported in this source |
| Effect of the longer refill interval | Did not hurt colony elimination 9 | Baseline for comparison 9 |
IGR baits take months because termites must feed, share the bait and then try to molt. The slow pace is what lets the bait spread, since a fast poison would kill foragers before they fed the rest of the colony.
Where you will see IGRs
On flea products. UC IPM says the most effective flea products contain the IGR methoprene or pyriproxyfen 2. See our flea and tick treatment page.
In termite bait stations. The EPA names diflubenzuron, hexaflumuron, lufenuron and noviflumuron among the most common termite bait ingredients; the fifth it lists, hydramethylnon, is not an IGR 8.
In bed bug plans. UC IPM names hydroprene among newer bed bug products 3. Our bed bug treatment page covers full plans.
In mosquito larvicides. The EPA names methoprene as an IGR that prevents mosquito larvae from maturing into adults 6. See our mosquito control page.
On the label. The active ingredient line names the IGR, often next to an adult-killing ingredient.
Benefits and trade-offs
What IGRs do well
Limitations
You will still see pests for a while. UC IPM says an IGR flea spray kills larvae but not pupae, so fleas may keep emerging for up to two weeks. It advises keeping up vacuuming and not reapplying for at least several weeks 2.
IGRs rarely work alone. UC IPM says room foggers lack long-term flea control unless they contain an IGR 2, and flea collars may pair IGRs with an adult-killing ingredient 2. Bed bug plans add heat, monitoring and other classes 3.
They are not quick fixes for nuisance adults. If wasps, adult cockroaches or ants are the problem today, an IGR alone does not end it. See residual insecticides and pest baits for other tools.
What drives cost, and how long IGRs last
IGR treatments are not priced here; we would need many sourced, dated local quotes to print a fair number.
The cost drivers are the pest and the plan. Flea work adds the pet’s treatment and a follow-up. Termite baiting adds a yearly service contract, because stations must be checked and refilled. Bed bug plans add visits because IGRs act slowly.
How long an IGR keeps working depends on the product and setting.
UC IPM says environmental flea IGRs are designed for long-term control of eggs and immature fleas 2, and lufenuron for pets is given monthly or by injection every six months 2.
Our pest control cost guide and termite cost estimator show what moves a quote.
How an IGR treatment usually runs
Fleas are the most common home use, and UC IPM guidance gives a typical treatment flow.
- Treat the pet. Use a vet-recommended product on every pet. Lufenuron, for example, stops flea reproduction but does not kill adult fleas 2.
- Clean first. Vacuum floors and furniture and wash pet bedding before treatment.
- Treat the home with an IGR product. A licensed pro, or you following the label, applies a product that contains an IGR 2.
- Expect emergence. Fleas may keep emerging for up to two weeks; keep vacuuming 2.
- Wait before re-treating. UC IPM advises not reapplying for at least several weeks 2.
- Fix the outdoors. Immature fleas rarely survive in sunny areas, so opening up shady pet resting spots helps 2.
Pet products are species-specific
Use only products labeled for your pet’s species and size, and never put a dog product on a cat.
Some flea collars pair IGRs with adult-killing ingredients such as permethrin 2, which cats are sensitive to. For a pet reaction, call your vet.
If a person is exposed to a flea product, call Poison Help at 1-800-222-1222; call 911 in an emergency.
Keeping an IGR plan on track
IGRs reward patience and steady follow-through.
- Keep vacuuming during the emergence window after a flea treatment 2.
- Keep every pet on its flea product on schedule; one untreated pet restarts the cycle.
- For termite baits, keep the service contract active so stations get refilled 9.
- For bed bugs, keep checking interceptors weekly, because IGRs act slowly 3.
- Record each product and date so a technician can plan rotation.
Judge results in weeks
Seeing adults in the first two weeks after an IGR flea treatment is expected 2. Judge the plan by whether new adults stop appearing after that.
Health and environmental risks
People. The EPA’s 1991 methoprene review found very low oral and breathing toxicity, no eye or skin irritation and no developmental or reproductive effects. It noted increased liver weights in test animals at high doses in some studies 5.
Pets. Merck says lufenuron is considered safe for dogs and cats, and pyriproxyfen has low mammal toxicity, though very high doses may affect the liver 1.
Water life. The EPA found methoprene highly toxic to estuarine invertebrates and flagged the slow-release briquette form for further study 5.
Our pesticide safety guide covers safe storage, and pesticide poisoning lists warning signs.
Rules that apply to IGRs
Federal (EPA, FIFRA). IGRs are registered pesticides with labels like any other.
Methoprene was first registered as a conventional pesticide in 1975, had a Registration Standard in February 1982 and was later reclassified as a biochemical pesticide.
The EPA’s Reregistration Eligibility Decision fact sheet (738-F-91-104, March 1991) found all methoprene-only products eligible except the briquette or slow-release form, which needed more study 5.
Food tolerances. Legal residue limits for methoprene on raw farm commodities are set in 40 CFR 180.359 5.
Pet products. Pills and injections such as lufenuron are veterinary products, given through a vet 2.
State. States register products and license applicators; see pest control licensing.
IGRs vs nerve-acting insecticides
| Feature | Insect growth regulator | Pyrethroids and neonicotinoids |
|---|---|---|
| Target | Development and molting 1 | Nerves |
| Kills adults | Hormone analogs do not 1 | Yes, on contact or feeding |
| Speed | Slow: days to months 39 | Fast knockdown |
| Mammal toxicity | Low; mammals lack the JH system 1 | Varies; see each page |
| Use with other tools | Often paired with an adulticide 2 | Often paired with an IGR 2 |
Compare the nerve-acting classes on our pyrethroids and neonicotinoids pages.
Common misconceptions
- Myth If I still see adults, the IGR failed.
- Reality Hormone analogs do not kill adults, and fleas can emerge for up to 2 weeks 12.
- Myth IGRs work in a day or two.
- Reality Bed bug IGRs may take many days; termite baits take months 39.
- Myth Low toxicity to people means no environmental risk.
- Reality The EPA found methoprene highly toxic to estuarine invertebrates 5.
- Myth Any flea fogger gives lasting control.
- Reality UC IPM says foggers lack long-term effect unless they contain an IGR 2.
- Myth Re-spraying sooner speeds things up.
- Reality UC IPM advises waiting at least several weeks before reapplying for fleas 2.
How climate changes the picture
Because IGRs act on development, local climate shapes how fast they show results. Insects grow faster in warmth.
The termite study behind the example found that, for eastern subterranean termites, colony elimination took more than twice as long when baiting began from September to March than from April to August 9.
Fleas follow the same logic: UC IPM notes immature fleas rarely survive in sunny areas 2, so warm, shaded, humid spots are where treatment matters most. Expect slower results in cool months and plan follow-ups to match.
When an IGR is the right tool
An IGR fits when a pest is breeding inside your home or near it and you want to stop the next generation: fleas in carpets, bed bugs in a long treatment plan, termite colonies via bait, or mosquito larvae in standing water you cannot drain.
An IGR alone fits poorly when you need adults gone today, so ask for a plan that pairs the IGR with something that removes adults, and set expectations for a few weeks of tail-off.
Ask any company which IGR it will use, what it is paired with, and when you should expect to stop seeing pests. Our guide to choosing a pest control company lists more questions.
Quick decision guide
Fleas indoors: use a product with an IGR plus pet treatment, and expect 2 weeks of emergence. Termites: choose an IGR bait if you accept months and a service contract. Bed bugs: use an IGR as one part of a full plan. Need adults gone now: pair the IGR with another method.
Questions about Insect Growth Regulator (IGR)
What is an insect growth regulator?
An insect growth regulator, or IGR, is an insecticide that disrupts how insects develop instead of killing adults on contact. Some copy a hormone that keeps insects from maturing into breeding adults. Others block the shell-building material chitin, so young insects die when they molt. Methoprene, pyriproxyfen and hydroprene are common examples.
Are insect growth regulators safe for pets?
IGRs are generally low in toxicity to mammals, because mammals do not have the juvenile hormone system IGRs target. Merck notes lufenuron is considered safe for dogs and cats and pyriproxyfen has low mammal toxicity. Use only products labeled for your pet’s species, since some collars pair IGRs with other insecticides.
Do IGRs kill adult fleas?
Most do not. Juvenile hormone analogs such as methoprene and pyriproxyfen stop immature fleas from maturing, and lufenuron stops flea reproduction without killing adults. UC IPM says the most effective flea products contain an IGR, often alongside an ingredient that kills adults.
How long do insect growth regulators take to work?
IGRs are slow by design. After an IGR flea spray, fleas may keep emerging for up to two weeks. UC IPM says bed bug IGRs may take many days. In a termite study with an IGR bait, the median time to eliminate a colony was 74 days with quarterly refills.
What is the difference between methoprene and pyriproxyfen?
Both are juvenile hormone analogs that stop insects from maturing into breeding adults. Methoprene is used against mosquitoes, flies, moths, beetles and fleas, the EPA says. Pyriproxyfen is commonly used for flea control on pets, per Merck. Product labels set where each may be used.
Are IGRs used for termites?
Yes, in bait stations. The EPA lists diflubenzuron, hexaflumuron, lufenuron and noviflumuron among termite bait ingredients, and UC IPM says the most effective termite baits use IGRs to suppress or destroy the colony. Termites die when they try to molt, after sharing the bait with nestmates.
Can I use an IGR for mosquitoes?
IGRs such as methoprene are used as mosquito larvicides that prevent larvae from maturing into adults, the EPA says. They do not affect adult mosquitoes biting you now. Draining standing water weekly is the first step; for treating water you cannot drain, follow the product label or hire a licensed pro.
Why should I wait before re-treating for fleas?
UC IPM says an IGR flea spray kills larvae but not pupae in cocoons, so fleas can keep emerging for up to two weeks. Re-spraying does not speed that up. It advises vacuuming during this time and not reapplying for at least several weeks.
Are IGRs harmful to the environment?
Some can be. The EPA found methoprene low in toxicity to people and most non-target species but highly toxic to estuarine invertebrates, and it required more study of the slow-release briquette form. Keep products out of drains and waterways unless the label allows aquatic use.
Sources
- Merck Veterinary Manual, Insect Growth and Development Regulator Toxicosis in Animals (Gupta and Doss; reviewed August 2022, updated September 2024), retrieved .
- UC Statewide IPM Program, Pest Notes: Fleas (Publication 7419), retrieved .
- UC Statewide IPM Program, Pest Notes: Bed Bugs (Publication 7454), retrieved .
- UC Statewide IPM Program, Pest Notes: Subterranean and Other Termites (Publication 7415), retrieved .
- U.S. EPA, R.E.D. Facts: Methoprene (738-F-91-104, March 1991; archive), retrieved .
- U.S. EPA, Controlling Mosquitoes at the Larval Stage, retrieved .
- U.S. EPA, Pesticides to Control Bed Bugs, retrieved .
- U.S. EPA, Termites: How to Identify and Control Them, retrieved .
- Eger et al., noviflumuron termite bait field study, Journal of Economic Entomology 105(2):533–539 (2012), retrieved .
Expert review
Written by the HyrePest Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: IGR groups, examples and mammal toxicity are from the Merck Veterinary Manual. Flea guidance is from UC IPM Pest Notes 7419; bed bug and termite IGR notes are from UC IPM 7454 and 7415.
Methoprene’s regulatory history and toxicity are from the EPA’s 1991 RED fact sheet (an archived document; labeled with its date). Mosquito larvicide facts are from the EPA. Termite timelines are from Eger et al. (2012). No doses, rates or prices are given.
Suggest a correction. We fix errors and say what changed.