Effects of two insect growth regulators on ecdysteroid production in Aedes aegypti (Diptera: Culicidae)

Diflubenzuron and OMS 2017 are insect growth regulators that affect larval to adult development in Aedes aegypti (L.) by altering ecdysis. When larvae were exposed to sublethal concentrations, surviving adults express reduced reproductive potential. In mosquitoes, ecdysteroids are important in larval and adult ovarian development. We applied 30% emergence reduction concentrations (EI30) of OMS 2017 and diflubenzuron to 4th-instar Ae. aegypti to determine if changes in ecdysteroid production may explain these physiological effects. Ecdysteroid concentrations were measured in the larvae, pupae, and adults after treatment with both IGRs. After treatment with OMS 2017, the 1st peak of ecdysteroid production in larvae was totally inhibited, but after pupation, ecdysteroid concentrations were the same as in untreated controls. In diflubenzuron-treated larvae, the second peak of production was delayed and the ecdysteroid concentrations of the larvae, pupae, and adults were depressed slightly when compared with untreated controls. The production of ecdysteroids by the ovaries was not altered by sublethal larval treatment with both IGRs. Although OMS 2017 and diflubenzuron belong to the same chemical family, their mode of action apparently is different.