Despite extensive research on malaria for over a century, critical gaps remain in our understanding of the vectors; gaps that also limit our success in malaria control. We address some of the most critical gaps, namely the strategies used by African malaria mosquitoes to persist through the long dry season without surface waters for several months. Combining field and laboratory studies, our results provide compelling evidence that malaria vectors persist locally through the dry season by a form of dormancy (aestivation) and also engage in wind-assisted long-distance migration probably over hundreds of kilometers. These fundamental facets of vector biology have been controversial and, until now, were ignored due to insufficient evidence. 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. This year, we have completed and published a genetic study to trace the origin of A. coluzzii wet-season populations in the Sahel. Using SNPs in 13 mosquito samples including several time points over two years, we found that the genetic makeup of populations remained stable from the end of the wet season until after the first rains, providing evidence for aestivation in A. coluzzii. However, this study also revealed that during the late wet season, changes occur in the genetic makeup of populations suggesting long-range migration during the late-wet season. The limitations of this study included short duration of the study (two years) and limited genetic power (800 SNPs). Therefore, in collaboration with the Sanger Center (UK), we have submitted 2000 mosquitoes collected over 4 years to whole genome sequencing. The first set of results based on subset genotyping revealed that the late-dry season peak consists of mosquitoes that are distinctly different from the only likely source of migrants (the large rice irrigation area near Niono, approx. 150 km away), thus providing support that the late dry-season peak consists of locally aestivating mosquitoes that emerged from their hidden shelter to replenish nutritional reserves (Dao et al. 2014). Once the full sequence data be available several investigations leading to comprehensive answers on this and other questions are planned. Additional paper on the effect of adult diet, including dietary restriction and shifts in protein/carbohydrate ratio on adult longevity as a factor involved in aestivation has been completed and published (Faiman et al. 2017). Additionally, a study on the effect of photoperiod on the induction of aestivation in A. coluzzii (Huestis et al. 2017) has been accepted for publication. Finally, an analysis of seasonal variation in mosquito microbiome composition in Sahelian and riparian mosquitoes has been completed (Krajacich et al.) and the paper will be soon submitted to a journal. Analysis is in progress on mosquitoes flying in high altitudes (50-250 m above ground) using traps tethered to helium filled balloons. Using HYSPLIT meteorological models, we can track mosquitoes backwards and forward and infer flight trajectories and putative source populations. With this tool, we can complete the analysis and writing of at least 3 publications. In additional to anopheline mosquitoes, we collected nearly 3000 culicine mosquitoes, many of which might be vectors of arboviruses. Using COI barcode analysis carried out in our lab and in the Walter Reed Biosystematic Unit by Yvonne Linton group, we have identified 1000 culicine mosquitoes members of >20 species with notable arbovirus (e.g., Rift Valley, West Nile) vectors among them. Additionally, sorting insects collected in high altitude, we identify and quantify pest insects in agriculture affecting food security. These including insects that vector viruses and bacteria to rice, maize, sorghum, and millet. These will be also analyzed to demonstrate the value of this aerial collection and linked data to the scientific community and encourage members to use the collection their own independent studies. This year, we have completed a study on flight aptitude of >1200 wild mosquitoes in Mali. Preliminary reuslts reveal that mosquitoes can keep flying up to 8 hours in the 9 hours assay. Further as predicted A. gambiae has exhibited greater flight aptitude than A. coluzzii. Similarly, flight aptitude varied seasonally in agreement with high altitude sampling. Finally, we have completed the first study to marking natural mosquitoes with stable isotopes. Following our laboratory experiment, we have enriched water in natural larval sites with deutorium. Our results from this first field application have revealed that adult emerging from these mosquitoes have exhibited significantly (>4x) higher concentrations of deutorium over the natural concentration and retained the enrichcment through the longest time we have tested. These results are very encouraging and may lead to an effective method for tracking wild mosquitoes over time and space. These results and ongoing studies using novel approaches (e.g., high altitude sampling, the stable isotopes enrichment for tracking wild mosquitoes) provide fresh insights in malariology and vector biology. The findings that Anopheline vector of malaria and other disease vectors engage in long-distance flights and some aestivate open new frontiers of basic and applied research.
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