Insect growth regulators, or IGRs, are chemicals that are used in some insecticides to control certain insects. Unlike many other insecticides, they are not nerve agents and they generally do not harm adult insects. Instead, they hinder the ability of immature insects to develop into healthy adults. Depending on the insect, eggs may not hatch, wings and other body parts may be deformed, molting might cease, and adults may become sterile or stop producing eggs. IGRs are also less likely to affects other organisms, including people, since they work on hormone pathways that are specific to insects.

Some IGRs known as juvenoids, or juvenile hormone analogs, work by mimicking insect hormones. However, an international team of scientists has discovered natural compounds in plants called juvenile hormone antagonists (JHANs) that instead work by counteracting the hormones. Their research appears in the Proceedings of the National Academy of Sciences.

The scientists screened 1,651 plant species and chose active JHANs from these plants. They then identified five JHANs from two plants that are effective in causing mortality of yellowfever mosquito (Aedes aegypti) larvae, specifically by retarding the development of ovaries.

“Our experiments showed that these five JHANs are effective against yellowfever mosquitoes,” said Alexander Raikhel, a distinguished professor of entomology at UC Riverside. “Our Korean collaborators, led by Sang Woon Shin at Seoul National University, are testing the effect of these five molecules on other agricultural pests. These newly-discovered natural molecules could lead to the development of a new class of safe and effective pesticides to control mosquitoes and, we expect, other agricultural pests.”

In addition to spreading yellow fever, Aedes aegypti also vectors dengue and chikungunya.

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– Identification of plant compounds that disrupt the insect juvenile hormone receptor complex