Malaria remains one of the top global-heath priorities, but, despite extensive research for over a century, outstanding gaps remain in our understanding of the vectors, which limit our ability to control malaria. Our research program is designed to address some of the most critical gaps, namely the strategies used by African malaria vectors to persist through the long dry season without surface waters for several months. Combining field and laboratory studies, our results provided compelling evidence that certain malaria vectors aestivate during the long dry season in the Sahel, while others engage in long-distance migration probably over hundreds of kilometers. These fundamental facets of vector biology have been controversial and, until now, could not be resolved. Conventional and novel malaria and vector control strategies cannot afford to ignore aestivation and long-distance migration as processes that may hinder or aid the ultimate outcome. Evidence based on mosquito mark-release-recapture experiments, patterns of long-term population dynamics, seasonal variation in spatial distribution, aerial mosquito sampling (40-200 m above ground), seasonal changes in reproductive activity, flight activity, cuticular hydrocarbons, and responses to changes in photoperiod and temperature, suggests that Anopheles coluzzii undergo aestivation during the Sahelian dry season, whereas A. arabiensis and A. gambiae s.s. re-colonize the area via wind-assisted long distance migration after the first rains. Experiments designed to further test this picture and address particular questions, including (i) where are the refugia used by aestivating A. coluzzii mosquitoes during the dry season include wells, and (ii) what weather systems are associated with mosquito flights in the lower jet stream (10--200 m above ground) have been carried out. Aerial sampling of mosquitoes using traps tethered to helium filled balloons has been a method we have been able to collect dozens of mosquitoes flying in the lower jet stream among them at least 6 A. gambiae s.l. More than 15 tanks of (balloon grade) helium have been used as part of this work.
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