Current Research Projects:

• Population dynamics and seasonal variation is spatial distribution of An. gambiae in the Sahel (led by A. Dao and A.S. Yaro)
  

  In Africa, malaria is transmitted primarily by Anopheles gambiae and A. arabiensis. These vectors exploit diverse environments including semi-arid areas, where surface waters required for larval development are absent for several months a year. How mosquitoes persist throughout the long dry season has been debated for decades. Recent evidence showed that the M form A. gambiae aestivate (extended survival throughout the 6 month dry season), but the role of migration from distant areas remained unresolved. We analyze the vector population dynamics and spatial distribution in a Sahelian village from 2008 to the present to discern its annual cycle and decipher the processes that shape it. The spatial mosquito distribution during this period showed higher aggregation during the dry season. The high-density houses during the dry season differed from those of the wet season. One or two adjacent hotspots were detected in the dry season and their location remained stable between years. Season-specific, stable, and focal hotspots are consistent with the predictions based on local shelters used by aestivating mosquitoes. Targeting mosquitoes in their aestivation shelters may be highly cost-effective, once we can find these shelters.

• Identifying phenotypic changes associated with seasonality and aestivation (led by D. Huestis and A.S. Yaro)
  

  Environmental variation over the course of a year (seasonality) can lead to phenotypic variation within a year and between locations experiencing different environmental patterns. This variation can be due to plasticity within a population and/or genetic divergence between populations – both of which are driven by natural selection of local environmental conditions. In the Sahel, we observe distinct seasonality between the wet season and the dry season, and hypothesize that mosquitoes are aestivating to survive the long, hot, dry season. Thus, we have designed a series of phenotypic assays to identify changes in metabolism, flight activity, feeding response, and oviposition between wet-season and dry-season individuals. The ultimate goal of these projects is to identify traits which will allow us to distinguish between individuals which are not aestivating from those which are in aestivation (or destined for aestivation or emerging from aestivation).

• Identifying molecular changes associated with seasonality and aestivation (led by D. Huestis)
  

  Along with identifying phenotypic differences associated with seasonality, we are also undertaking several projects to explore changes at the molecular level that may result from plasticity or other responses to differing environmental conditions. Specifically, we will be analyzing changes in gene expression, nutritional reserves, and cuticular hydrocarbons with respect to seasonality. Specimens have been collected in both the wet season and the dry season for use in RNA analyses, which may include microarrays, real-time PCR of candidate genes, and next-generation high-throughput sequencing. Additionally, mosquitoes have been collected and preserved for nutritional analysis to compare the total protein content and the lipid and carbohydrate reserves of wet-season vs. dry-season individuals. Lastly, we hypothesize that the cuticular hydrocarbon (CHC) profiles between individuals in aestivation should be significantly different from non-aestivators, both as a barrier to moisture-loss and due to age, and are conducting gas-chromatography to obtain these CHC profiles.

• Finding the hidden shelters used by malaria vectors (Led by A. Dao and A.S. Yaro)
  

  During the dry season, extensive searches were undertaken to find mosquitoes inside wells, rodent burrows, termite mounds, tree-holes, toilettes, granaries, and virtually any hole in and around houses. However, very few mosquitoes were discovered. Recently, we have employed sniffing dogs, expertly trained by Mr. Sapir Weiss (Olivet Kennel & Dog Training Resort, Santa Rosa, CA) to detect naturally-caught and scent-tagged mosquitoes after their release. The sensitivity and specificy of the dogs were over 90% under field conditions as measured by blind tests. Several putative shelter were indicated by the dogs and are being evaluated to determine if they harboured mosquitoes. The study has been funded in large part by the Tamaki Foundation.

• Long-distance migration of malaria vectors (Led by A. Dao and D. Huestis)
  

  The possiblity of long-distance migration of malaria vectors is being addressed based on monitoring rapid changes in density and composition along transects over 100 km long and aerial sampling reaching 200 m above ground. Monitoring is conducted synchronously across 8 villages every 2 days or every 2 weeks, depending on changes in density observed on the ground. This component allows for dissecting sequence of rapid changes (waves) in mosquito density to be tracked. The aerial sampling of mosquitoes is aimed at detecting seasonal migrations of these mosquitoes at altitudes of 10-200 m, in relation the the changes on the ground. The study has been funded in part by the Bill and Melinda Gates Foundation through a grant to Dr. Frank Collins and colleagues at Notre Dame.

• Swarming and mating behavior of the molecular forms of An. gambiae and An. arabiensis(led by A.S. Yaro)
  

  The extent of reproductive isolation between the molecular forms of An. gambiae is the focus of much debate. Positive assortative mating has been detected under natural conditions (Tripet et al. 2001), but the mechanism that mediates it is unknown. Our study aims at identifying differences in the forms mating systems that facilitate their assortative mating. Spatial and temporal segregation between swarms of the molecular forms in sympatric areas are investigated along with within-swarm mate recognition cues.

• Does oviposition deprivation make dangerously old and mean mosquitoes? (Led by M. Artis)

  The African malaria mosquito, Anopheles gambiae, needs surface water to lay their eggs; when this is compromised in the dry season or during shorter dry spells, mosquitoes take specific yet unknown measures to increase their longevity until larval sites can be found. The longer a female mosquito survives, the more dangerous she becomes due to higher probability she will acquire and transmit malaria. In the Sahel region of Africa, there are long and short dry periods where larval sites are not available, and, during this time, mosquitoes are oviposition-deprived. Previous work by our group demonstrated that egg-laying and hatch rates were greatly reduced following oviposition deprivation but could be rescued by additional blood meals (Dieter et al. 2012). The effect of oviposition deprivation on longevity and feeding rate of A. gambiae in the focus of this project.

• Can seasonal changes in photoperiod and temperature induce dry-season diapause in the African malaria mosquito? (Led by D. Huestis)
  

  In the Sahel the dry season lasts 5-7 months, during which no oviposition sites are available. The mechanisms of population persistence during these harsh environmental conditions are still largely unknown; however, our previous work has indicated that M-form A. gambiae likely undergo aestivation (dry-season diapause) while S-form A. gambiae and A. arabiensis populations are maintained by seasonal migration. The rapid changes in photoperiod that occur in the Sahel when larval sites begin to dry could be the environmental signal used by mosquitoes to induce the physiological and behavioral changes that underlie diapause. To test this hypothesis, we established new mosquito colonies from our Malian field site and simulated the actual seasonal shifts in photoperiod at this location using light boxes (simulating the wet season, transition period, and dry season). Our data suggest that seasonal shifts in photoperiod do affect phenotypic traits of these taxa and thus photoperiodic cues could be utilized by mosquitoes in the field to initiate life-history changes in preparation for the dry season.