What is an insect growth regulator? I’ve read that this is supposed to be a better way to control pests without the use of insecticides. Why don’t exterminators use insect growth regulators? A. F., Millville, MA

Exterminators do use insect growth regulators (IGRs). We use them all the time and for different kinds of insects. In most cases though they are part of a pest management program that also uses regular insecticides but in lesser amounts. In fact, IGRs are considered to be insecticides themselves, although they are relatively nontoxic to humans and pets.

Insect Growth Regulators Block Normal Development

Once you understand how insect growth regulators work, you’ll understand why, in most cases, we use a combination treatment. And that’s what most customers prefer (see How Does an Insect Growth Regulator Work?). IGRs don’t kill insects outright. Instead they affect the development of the immature stage of the insect so that it doesn’t turn into an adult insect or it becomes a sterile adult that can’t reproduce. Other types of IGRs affect the insect’s ability to develop its outer shell during its final molt, killing it before it becomes a breeding adult.

Because of the way that they work, IGRs tend to work slowly. It takes a generation or more to see results as new insects fail to be produced. It also means that the insect pests that are present will still be around for awhile. If the immature stage is the damaging or annoying stage of the insect, an IGR used alone may not be acceptable for that reason. Exterminators will often mix an IGR with a residual insecticide that will kill most of the insects, leaving the IGR to provide long-term backup control for any survivors. An IGR usually remains effective for several months.

Insect Growth Regulators for Flea Control

Insect growth regulators are commonly used in flea control to prevent eggs from hatching and to prevent the nonbiting larvae from turning into biting adult fleas. The IGR is a chemical mimic of a hormone that, when levels drop, signals to the flea larva that it is time to pupate. The IGR keeps the hormone levels artificially high and the larvae never pupate. It’s important to know that an IGR does not kill adult insects, so adult fleas will continue to feed on the pet and must be controlled separately. See IGRs Used Early Stop Flea Development for Good.

IGRs used in cockroach control affect the nymphs so that they don’t develop into adult cockroaches, or they develop into sterile adults, or any eggs laid will not hatch. Again, unless the IGR is used along with a standard cockroach insecticide, you may have to live with the presence of IGR-treated roaches for a while.

IGRs are also available to treat mosquito larvae, ants, stored product pests, bed bugs, and termites. They are an important tool in the pest control arsenal. Insect growth regulators are a low toxicity backup to standard insecticides and allow us to reduce the time between insecticide treatments. Because they work differently, IGRs also provide an alternative control measure against insects that have become resistant to standard insecticides.

Photo credit: NY State IPM