Tracing the origin of the early wet‐season Anopheles coluzzii in the Sahel

Abstract

In arid environments, the source of the malaria mosquito populations that re‐establish soon after first rains remains a puzzle and alternative explanations have been proposed. Using genetic data, we evaluated whether the early rainy season (RS) population of Anopheles coluzzii is descended from the preceding late RS generation at the same locality, consistent with dry season (DS) dormancy (aestivation), or from migrants from distant locations. Distinct predictions derived from these two hypotheses were assessed, based on variation in 738 SNPs in eleven A. coluzzii samples, including seven samples spanning 2 years in a Sahelian village. As predicted by the “local origin under aestivation hypothesis,” temporal samples from the late RS and those collected after the first rain of the following RS were clustered together, while larger genetic distances were found among samples spanning the RS. Likewise, multilocus genotype composition of samples from the end of the RS was similar across samples until the following RS, unlike samples that spanned the RS. Consistent with reproductive arrest during the DS, no genetic drift was detected between samples taken over that period, despite encompassing extreme population minima, whereas it was detected between samples spanning the RS. Accordingly, the variance in allele frequency increased with time over the RS, but not over the DS. However, not all the results agreed with aestivation. Large genetic distances separated samples taken a year apart, and during the first year, within‐sample genetic diversity declined and increased back during the late RS, suggesting a bottleneck followed by migration. The decline of genetic diversity followed by a mass distribution of insecticide‐treated nets was accompanied by a reduced mosquito density and a rise in the mutation conferring resistance to pyrethroids, indicating a bottleneck due to insecticidal selection. Overall, our results support aestivation in A. coluzzii during the DS that is accompanied by long‐distance migration in the late RS.

Modelling the persistence of mosquito vectors of malaria in Burkina Faso

“…In the case of An. coluzzii , recent genetic data from a Malian Sahel village (the same study site as [ 8 ]) has suggested that this population survives the dry season predominantly by aestivation (in agreement with [ 8 ]), yet long distance migrants also arrive over the course of a rainy season [ 15 ]. However, two studies comparing populations of An.…”

“…There is mounting evidence that this behaviour plays a role in the persistence of some An. coluzzii populations [ 8 , 11 – 15 ], though there remains less evidence that other anophelines aestivate [ 8 ]. Second, localities might be colonised at the start of the rainy season by mosquitoes dispersing from nearby locations where there are persistent populations owing to year-round surface water.…”

Pilot Suppression trial ofAedes albopictusmosquitoes through an Integrated Vector Management strategy including the Sterile Insect Technique in Mauritius

“…While the maximum distance travelled by Ae. albopictus females in some dispersal studies ranged between 150 and 800 m 51,52,53,54 , wind-mediated migration of some mosquito species has also been expounded by others 38,55,56,57,58,59,60,61,62 .…”

Massive windborne migration of Sahelian insects: Diversity, seasonality, altitude, and direction

“…1): Thierola (13.6586, - 7.2147) and Siguima (14.1676, −7.2279; March 2013 to November 2015); Markabougou (13.9144, −6.3438; June 2013 to June 2015), and Dallowere (13.6158, −7.0369; July to November 2015). The study area has been described in detail previously (Lehmann et al, 2010; Huestis et al, 2012; Yaro et al, 2012; Dao et al, 2014; Lehmann et al, 2017). Briefly, it is a rural area characterized by scattered villages, with traditional mud-brick houses, surrounded by fields.…”