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How Does an Insect Growth Regulator Work?

By Chris Williams on November 5, 2013.

IGR for german cockroachesQuestion

How does an insect growth regulator work to kill cockroaches? My friend says her pest control guy uses a growth regulator in her apartment. Does that mean you just end up with lots of little roaches that never grow up!!?

Answer

As their name suggests, insect growth regulators are insecticides that affect a cockroach’s ability to grow. With these products, instead of killing the cockroaches, you actually are allowing the roaches to survive (for a while) in order to prevent future generations.

Insect growth regulators (we call them IGRs) are long-lasting, low-risk insecticides that are relatively nontoxic to humans and pets. Pest management companies regularly use IGRs to help control cockroaches, fleas, ants, food pests, mosquitoes, bed bugs, termites, and others.

There are different types of IGRs that affect insects in different ways, but all disturb the life cycle of the insect in some way by interfering with its hormones. Some IGRs affect immature insects by blocking their ability to molt into mature adults, and some block the adult insect’s ability to reproduce.

Cockroach nymphs that are exposed to an IGR never molt into adults or they develop into sterile adults that cannot reproduce. IGRs can also affect insects that are exposed later, in the adult stage, by blocking the development of eggs. Eggs that are exposed to IGRs will not hatch.

An important thing to know about IGRs is that they do not kill cockroaches outright. You might still see cockroaches after a treatment with an IGR. You have to have faith in the long-term goal—that those cockroaches will be unable to reproduce. Although no new young will be produced, most of the current crop of cockroach nymphs and adults will have to die off naturally…if an IGR is used alone.

So, Why Even Use a Growth Regulator?

Because most people are not happy waiting for weeks for their cockroaches to disappear, IGRs are rarely used alone. They are combined with another pesticide that will provide immediate kill of cockroaches.

Then why even use an IGR? Because any cockroaches that survive the pesticide treatment will be affected by the long-lasting IGR and will eventually die as a result without reproducing. IGRs are a low toxicity backup to standard insecticides. They are also useful when a cockroach population is showing resistance to standard insecticides. Because IGRs work in a different way, they can still affect cockroaches when other insecticides are giving poor results.

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