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 migration probably over hundreds of kilometers per night. These 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 control of the disease. This year, we have published a study on a novel method to track mosquitoes over extended time based on enrichment of natural larval sites with stable isotopes (deuterium, 2H), which results in adults mosquitoes that are marked, for life, by a higher concentration of the 2H: (Faiman et al. 2019: Methods in Ecology & Evolution). A follow up of this study to evaluate the contribution of aestivation in the Sahel by tracking mosquitoes from the end of the wet season through the dry season and until the beginning of the subsequent wet season is being completed. Our results reveal a dramatic picture. By early November 2017, when the last larval sites dried up, we marked 60% of the adult mosquitoes in two Sahelian villages. Isotope ratio mass spectrograph (IRMS) analysis has revealed that 25-40% of the mosquitoes appearing in March during the late dry season peak had levels of 2H above natural levels, i.e., they grew up as larvae in the enriched larval sites 4 months earlier and >15% had elevated levels of 2H after the first rains (end of June 2018). The complete results, present direct evidence that (i) A. coluzzii appearing during the late dry season peak consists of aestivators, rather than long-distance migrators, (ii) the survival of local mosquitoes for 4 months strongly supports aestivation as the main persistence strategy of A. coluzzii, and (iii) this novel way of marking mosquitoes is powerful to elucidate other critical problems in vector-borne disease. Additional mosquitoes are analyzed by IRMS. The paper describing these exciting results is being written. Novel methods were also used to mark and track adult mosquitoes using a combination of novel fluorescent dye (SmartWater) containing DNA tags. This application of this method was developed in the laboratory, showing great adventages over conventional methods. In collaboration with LMIV (Patrick Duffys Lab), we are providing entomological evaluation of the movement of mosquitoes between houses in the Malian village, Doneguebougou, which were assigned for transmission-blocking-vaccine in comparison to placebo treatment. This mark-release-recapture experiment has a unique design tailored to determine quantitate the movement of mosquitoes that can undermine the measurement of the vaccine efficacy. Further, our experimental design is aimed to identify the units of malaria transmission in a village and determine how many such units exist in a typical village. Our first paper the on aerial sampling of mosquitoes entitled: Windborne long-distance migration of malaria mosquitoes in the Sahel is Nature: In Press). The results focus on primary and secondary malaria mosquitoes that were found flying in altitudes (40-290 m above ground). These important and findings include evidence that most mosquitoes are females after their blood meal, indicating that human and animal pathogens are being transported by these mosquitoes over hundreds of kilometers per night. In additional to anopheline mosquitoes, we collected approximately 2,500 culicine mosquitoes, many of which might be vectors of arboviruses. Using COI barcode analysis carried out in our lab and in the Walter Reed Biosystematics Unit (Yvonne Lintons group). The identification, which has recently been completed reveal >30 mosquito species including vectors of filariae and arboviruses (e.g., Rift Valley Fever, West Nile). This second paper is being drafted. Among the insects collected in high altitude, we identified and quantified pest species in agriculture affecting food security, such as leafhoppers vectors of viruses and bacteria to rice, maize, sorghum, and millet. These are 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. Our manuscript on diverse insect taxa collected in high altitudes is circulating among co-authors. It will be submitted later this year. A paper describing innovative work on mosquito tolerance to pathogens, that was carried out in the lab in 2011, entitled Variation in Tolerance to Parasites Affects Vectorial Capacity of Natural Asian Tiger Mosquito Populations has been reviewed favorably by Current Biology. After revision, we are awaiting final decision. Experiments to simulate aestivation in the laboratory has have yielded encouraging results, with a combination of photoperiod, temperature, and priming of larvae leading to survival of A. gambiae s.l. over 100 days. These results are now being replicated with subsamples assays for variation in transcription, stress tolerance, and lipid content to further test the relation of this long-lived phenotype with aestivation. A transcriptomic analysis of mosquitoes samples representing different seasons from the Sahel and perennial area in the wet savanna of Mali is underway. Data analysis and writing is being completed on a study on flight aptitude of >1200 wild mosquitoes bio-assayed in Mali. The results reveal that mosquitoes fly over the 9 hours night assay, with maximum total flight of 5 hours. Variation between species over different seasons and relationships to morphometric traits may help clarify if some of the flights represent long distance migration. In brief, we carry out a set of novel studies to address the roles of dormancy and windborne migration in African mosquito vectors and develop new tools to better understand vector-borne disease transmission and control.
Showing the most recent 10 out of 12 publications
