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Insect Growth Regulators (IGRs)

Insect growth regulators (IGRs) are insecticides that mimic hormones in young insects. They disrupt how insects grow and reproduce. IGRs can control many types of insects including fleas, cockroaches, and mosquitos. Although they are rarely fatal for adult insects, they can prevent reproduction, egg-hatch, and molting from one stage to the next. Many IGR products are mixed with other insecticides that kill adult insects. IGRs are generally low in toxicity to humans.

How do IGRs work?

	Adults usually survive IGR treatments and continue to be a nuisance until they die naturally. However, the eggs they produce may not survive. Sometimes adults’ reproductive organs are affected and the adult becomes sterile.
	Eggs treated with IGRs may never hatch. If the eggs do hatch, the young insect may not survive.
	The larva, or worm-like stage, may not be able to develop correctly into an adult after exposure to IGRs. Some larvae may stay in this juvenile stage until they die.
	A case like a moth’s cocoon usually protects the pupa. Treatment with an IGR may prevent the pupa from becoming an adult and reproducing.

IGRs affect certain hormones in insects, hormones that humans don’t have. They don’t kill insects immediately, but they can stop a pest population from reproducing until all of the pests have died.

Keep these tips in mind:

• Be sure to read, understand, and follow all of the label directions when applying insecticides, including IGRs.
• Identify your insect first. Some IGRs may be more effective for certain insects than others.
• IGRs do not kill adult insects and using more of a product will not make it more effective. Always follow mixing instructions on the label.
• Try a combination of control methods. Integrated Pest Management helps reduce insect problems through prevention, sanitation, and exclusion.
• IGRs can also harm helpful insects like bees. Focus on specific problem areas to reduce risk to other insects.

Additional Resources:

• Insect Growth Regulators - Washington State University
• Selectivity of Insecticides and Miticides - UC IPM
• Bio-rational Pesticides - University of Massachusetts Extension
• How Insecticides Work - University of New Hampshire Extension

Information about specific IGR chemicals:

• Methoprene Fact Sheet - National Pesticide Information Center (NPIC)
• Methoprene Pesticide Fact Sheet - Environmental Protection Agency (EPA)
• Methoprene Fact Sheet - Extension Toxicology Network (EXTOXNET)
• Diflubenzuron RED Facts - Environmental Protection Agency (EPA)
• Neem Oil Fact Sheet - National Pesticide Information Center (NPIC)
• Pyriproxyfen Fact Sheet - National Pesticide Information Center (NPIC)

If you have questions about this, or any pesticide-related topic, please call NPIC at 800-858-7378 (8:00am - 12:00pm PST), or email us at npic@ace.orst.edu.