Isotopic evidence that aestivation allows malaria mosquitoes to persist through the dry season in the Sahel

Abstract

Data suggests the malaria vector Anopheles coluzzii persists in the Sahel by dry-season aestivation though its speci c contribution compared with alternative strategies, i.e., migration is unknown. We have marked Anopheles mosquitoes using deuterium ( 2 H) to assess the contribution of aestivation to persistence of mosquitoes through the seven-month dry season. If local aestivation is the only way An. coluzzii persists, the frequency of marked mosquitoes should remain stable throughout, whereas nding no marked mosquitoes would be evidence against aestivation. Larval sites were enriched with 2 H at the end of the 2017 wet season (September) in two Sahelian villages in Mali. We monitored 2 H-enriched populations until the onset of rains (June 2018). By the end of the enrichment period (November 2017), 33% of An. coluzzii mosquitoes were strongly marked. Expectedly, 2 H levels in marked mosquitoes degraded over time. We utilized three methods to estimate the fraction of marked mosquitoes in the population. Seven months following enrichment all three methods supported the presence of marked mosquitoes: 7% of the population had 2 H values above the highest pre-enrichment value. An excess of 21% exceeded the expected 25% in the 3rd quartile of the pre-enrichment population. Finally, a nite mixed population model showed 2.5% represented a subpopulation of marked mosquitoes with elevated 2 H, compatible with our predictions. We provide evidence that aestivation is a major persistence mechanism of An. coluzzii in the Sahel, contributing at least 20% of the adults at the onset of rains, suggesting either mixture among local populations or that An. coluzzii utilizes several persistence strategies. The implications for mosquito control and malaria elimination campaigns are highlighted.

Considerations for first field trials of low-threshold gene drive for malaria vector control

“…Assessment of genetic efficacy would occur over multiple generations post-release, as well as accounting for seasonal variability, particularly changes in rainfall that alter larval habitat availability, or larval migration via surface water movement that might influence the spread of the gene drive system. For example, the gene drive system might impose fitness costs so that the gene drive mosquitoes were less likely to survive the dry season, or simply be stochastically lost during this period due to the low densities of target mosquito populations arising from poor availability of aquatic habitats [ 132 , 133 ].…”

The potential of gene drive releases in malaria vector species to reduce the malaria burden in different African environments

“…We need to better understand dispersal in Anopheles to improve our predictions about rates of spatial spread of gene drives, and our analyses do not include possible long-range dispersal 55 , which could lead to gene drive constructs jumping across large areas to encroach into new regions with possible transnational movement. We also need more understanding of what mosquitoes do during the dry season in highly seasonal environments such as the Sahel – do they aestivate, persist in local refugia, or recolonise through long distance dispersal 56 ?. Previous modelling has indicated that aestivation may slow gene drive spread but not greatly alter the eventual suppression in an area 19 .…”

Small dams driveAnophelesabundance during the dry season in a high malaria burden area of Malawi

“…In certain areas (e.g. the Sahel), this leaves virtually no extant pools for oviposition, causing Anopheles populations to enter either a state of dormancy (aestivation) 4 or undergo wind-assisted migration 5 to maintain population viability. That said, in many parts of Africa, enough standing water persists into the dry season extending the malaria transmission season, disproportionately increasing the risk of those communities living in proximity to dry season habitat.…”