Insulin-like peptides regulate egg formation in Anopheles stephensi

Mosquitoes feed on blood to obtain nutrients required for egg production. In the dengue vector Aedes aegypti, blood-feeding triggers the brain to release insulin-like peptides (ILPs) and ovary ecdysteroidogenic hormone (OEH). These neuropeptides then stimulate the ovaries to synthesize ecdysteroids, which regulate production of yolk proteins that are packaged into developing oocytes. Less understood are the processes that regulate egg formation in anopheline mosquitoes, which transmit mammalian malaria parasites. To address this, we characterized the endocrine events that orchestrate egg formation in the Indian malaria vector Anopheles stephensi. Gain-of-function assays identified ILP3, ILP4 and 20-hydroxyecdysone (20E) as key factors that regulate egg formation in An. stephensi. Experiments comparing nutrient mobilization in blood-fed and sugar-fed females further suggest that unlike Ae. aegypti, An. stephensi lacks sufficient teneral reserves to produce yolk and relies more heavily on nutrients from the blood meal to produce eggs. These results allude to differences in reproductive strategies between mosquito species that should be considered when developing a targeted approach to malaria control.