Abstract Background Mosquito populations in peri-urban, agro-pastoral West African environments from the Soudano-Sahelian climate zone are thought to expand and contract spatially seasonally as rainfall affects the availability of hosts and larval habitats between villages. Currently, the extent of this phenomenon and how it affects different vector species is poorly known, due to the scarcity of effective outdoor sampling tools. Methods In this study, Biogent Sentinel Trap with Heat (BGSH) were deployed outdoors along a 2.5km transect extending from the village of Sogolombougou in Mali into rural and sylvatic habitats. Four traps were placed at 500m intervals and run overnight for 4 consecutive nights during each of four seasonal phases dry, dry-to-rainy, rainy and rainy-to-dry, across two years. Results A total of 3389 mosquitoes were captured. Culex quinquefasciatus (39.2%) and Ae. aegypti (39.0%) were the most abundant species captured, followed by An. coustani (11.1%), An. gambiae s.l. (6.9%), Mansonia sp. (3.6%), An. phaorensis (0.2%), and Toxorhynchites sp. (0.06%). Within An. gambiae s.l., An. gambiae s.s. and An. coluzzii were found in similar proportions, with only a few An. arabiensis. Only An. coluzzii and An. gambiae s.s. carried sporozoites. As predicted, mosquito populations greatly expanded during the dry-to-rainy and rainy season periods, but species differed in the timing and distance from the village at which they did. Notably, a higher proportion of An. coluzzii and gambiae s.s. were found within the village in the dry season, but they were still captured at all distances on the transect. In the dry-to-rainy and rainy periods, An. gambiae s.s. and Ae. aegypti were particularly abundant > 1 km away from the village, whilst An. coustani was common everywhere except in the village. Cx. quinquefasciatus was common at all distances throughout the year, regressing mostly in the dry season. Conclusion Our findings suggest that in Soudano-Sahelian seasonal African habitats, An. gambiae s.s. and coluzzii populations may not contract within settlements in the dry season as much as previously thought. The presence of host-seeking females, some sporozoite positive, outside of villages even in the dry season suggest that aestivation sites may be dispersed and this creates opportunities for mosquito movement and malaria transmission in agro-pastoral habitats.
Guindo et al. (Wed,) studied this question.