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Insect Growth Regulators
Beyond Pesticides Rating: Toxic

Insect Growth Regulators (IGRs), also called third-generation insecticides, are pesticides that disrupt the normal activity of the endocrine or hormone system of insects, affecting the development, reproduction, or metamorphosis of the target insect. They have a much slower mode of action than synthetic chemical insecticides. IGRs include juvenile hormone (JH) mimics and chitin synthesis inhibitors (CSIs). 

There is a large concern about the effect of IGRs on non-target species and many IGRs are lacking full health and safety data. 

Juvenile Hormones (JH)

Most currently registered IGRs, such as hydroprene and methoprene, fall into the juvenile hormone mimic category. These pesticides mimic the JH produced in the insect brain, which forces the insect to remain in a juvenile state. Normally, the production of the JH would ebb as the insect progressed through the nymphal stages until the final molt into the adult stage, when JH production would cease. When exposed to a JH mimic, the insect remains in an immature state, and is rendered unable to successfully molt into the adult stage or become reproductively viable. 

JH mimics are not be specific to the pest under attack, as the molecules based on the JH system are more or less common to all insect species. 

Chitin Synthesis Inhibitors (CSIs)

CSIs, such as hexaflumuron, lufenuron and diflubenzuron, inhibit the production of chitin, a major component of the insect exoskeleton. Insects treated with CSIs become unable to synthesize new cuticle, and therefore unable to successfully molt into the next stage. 

CSIs may be toxic to other arthropods, and IGR metabolites may have adverse effects on vertebrates due to their ability to bind to certain members of the nuclear hormone receptor family.           

Pest Resistance to IGRs

It was originally thought that insects would be unable to develop resistance to molecules that mimic their own hormones, but there is already evidence of developing resistance to several IGRs, including methoprene, hydroprene, kinoprene, pyriproxifen, and diflubenzuron. Resistance seems to result from decreased penetration and increased metabolism of the compound.  

For additional toxicity information, please see fact sheets on individual IGRs: diflubenzuron, hexaflumuron, hydroprene and methoprene.  

Resource:

Hoffman, K.H., Lorenz, M.W. 1998. Recent Advances in Hormones in Insect Pest Control. Phytoparasitica 26:4.