Long-lasting insecticidal nets are an effective tool in reducing malaria transmission. However, with increasing insecticide resistance little is known about how physiologically resistant malaria vectors behave around a human-occupied bed net, despite their importance in malaria transmission. This study assessed the host-seeking behavior of the major malaria vector Anopheles gambiae s.s, when an intact human-occupied treated bed net is in place, with respect to their insecticide resistance status under semi-field conditions. Pyrethroid resistant and susceptible females of Anopheles gambiae s.s were released inside a semi-field environment housing a hut which was occupied by a human host sleeping under treated or untreated bed net trap. Mosquitoes resting inside the hut or exiting and resting outside were collected using a prokopack aspirator, window exit trap and clay pots. The proportion of resistant females caught in the treated bed net trap was higher compared to the susceptible females (OR=1.445; P<0.00019). Resistant mosquitoes were less likely to exit the house when a treated bed net was present compared to the susceptible mosquitoes. The susceptible females were 2.3 times more likely to stay outdoors away from the treated bed net (OR=2.25; P<0.0001).The resistant mosquitoes showed significantly reduced avoidance behavior compared to the susceptible mosquitoes that were observed to exit the house and remained outdoors when a treated bed net was used. However, further investigations of the behavior of resistant mosquitoes under natural conditions should be undertaken to confirm these observations and improve the current intervention which are threatened by insecticide resistance and altered vector behavior.

This study employs landscape genetics to investigate the environmental drivers of a deadly vector-borne disease, malaria caused by Plasmodium falciparum, in a more spatially comprehensive manner than any previous work. With 1,804 samples from 44 sites collected in western Kenya in 2012 and 2013, we performed resistance surface analysis to show that Lake Victoria acts as a barrier to transmission between areas north and south of the Winam Gulf. In addition, Mantel correlograms clearly showed significant correlations between genetic and geographic distance over short distances (< 70 km). In both cases, we used an identity-by-state measure of relatedness tailored to highly-related individuals in order to focus on recent gene flow that is more relevant to transmission. To supplement these results, we also performed conventional population genetics analyses, including Bayesian clustering methods and spatial ordination techniques. These revealed some differentiation on the basis of geography and elevation and a cluster of genetic similarity in the lowlands north of the Winam Gulf of Lake Victoria. Taken as a whole, these results indicate low overall genetic differentiation in the Lake Victoria region, but with some separation of populations north and south of the Winam Gulf that is explained by the presence of the lake as a geographic barrier to gene flow. We recommend similar landscape genetics analyses in future molecular epidemiology studies of vector-borne diseases to extend and contextualize the results of traditional population genetics.