Induction of long-lived potential aestivation states in laboratory An. gambiae mosquitoes

Background: How Anopheline mosquitoes persist through the long dry season in Africa remains a gap in our understanding of these malaria vectors. To span this period in locations such as the Sahelian zone of Mali, mosquitoes must either migrate to areas of permanent water, recolonize areas as they again become favorable, or survive in harsh conditions including high temperatures, low humidity, and an absence of surface water (required for breeding). Adult mosquitoes surviving through this season must dramatically extend their typical lifespan (averaging 2-3 weeks) to 7 months. Previous work has found evidence that the malaria mosquito An. coluzzii, survives over 200 days in the wild between rainy seasons in a presumed state of aestivation (hibernation), but this state has so far not been replicated in laboratory conditions. The inability to recapitulate aestivation in the lab hinders addressing key questions such as how this state is induced, how it affects malaria vector competence, and its impact on disease transmission. Methods: We compared survivorship of mosquitoes in climate-controlled incubators that adjusted humidity (40-85% RH), temperature (18-27 °C), and light conditions (8-12 hours of light). A range of conditions were chosen to mimic the late rainy and dry seasons as well as relevant extremes these mosquitoes may experience during aestivation. Results: We found that by priming mosquitoes in conditions simulating the late wet season in Mali, and maintaining mosquitoes in reduced light/temperature, mean mosquito survival increased from 18.34 ± 0.65 to 48.02 ± 2.87 days, median survival increased from 19 (95% CI: 17-21) to 50 days (95% CI: 40-58), and the maximum longevity increased from 38 to 109 days (p-adj