What are Insect Growth Regulators and do they work?

This question came in from Gray:


We hate fleas and take action to kill on sight. This year's flea season was late but vicious here in NC. Besides our usual arsenal of diatoms in the yard and K-9 Advantix on the dog, plus pyrethrum based flea shampoo, we are trying "I.G. Regulator", a hormonal based product that is supposed to stop flea development at the larval stage. Insects exposed to this never develop into adults (according to the label). It is supposed to be safe for anything besides bugs. Spray it everywhere, let it dry and bugs never grow up. Do you have any info on this stuff? I'm a little worried that it is "hormonal". But then, I never plan to grow up anyway! They claim its good for seven months. The brand we got is "Martin's I. G. Regulator Concentrate with Nylar". We'll let you know."


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My response:

Insect growth regulators generally are any kind of chemical that interferes with the ability of insects to proceed to the next stage of their life. Most insects start out as eggs, then turn into larva, then pupa, then to an adult. An IGR will stop them from going through one of those stages. Some are also designed to stop insects from molting - they are called "chitin inhibitors" and will prevent them from growing because they can't build a new, bigger exoskeleton. When they try to molt, they die.

Martin's I.G. Regulator is a chemical called Nylar (also called Pyriproxifen). It does not kill adult fleas, but it stops both eggs and larva from proceeding to the next stage of growth. It's a good idea to combine it with other products like you're doing, because it won't do anything about adults. However, you can use it before flea season even starts, and it will help prevent you from getting an infestation - even if some adult fleas get on your pet, any eggs they lay won't turn into other adults. I looked into the claim about working for seven months, and according to an article by a professor at the LSU Veterinary School, it has worked for up to eleven in testing. There were earlier chemicals used that were essentially the same, but broke down from UV rays in light and could not be used outdoors. Nylar fixed this problem and is a more stable chemical that does the same thing to insects.

As far as whether you need to be concerned about it, mammals generally don't have problems with insect growth regulators. While they do work on hormones, they work on hormones that exist in insects but not in mammals. Basically, pyriproxifen is a chemical that is very similar to a hormone in insects that they need to grow. It tricks the insect's body and interferes with the growth process. Since people and pets don't have a hormone like that, you aren't going to be affected.  You still need to avoid getting any in your eyes, etc., but it is otherwise safe to be around. One caveat, though, is that it works on other insects and is very deadly to fish if you get it in their water. So if you have an aquarium or if you are using this outside and are worried about friendly bugs, you should be more careful with it.

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