Geographically extensive larval surveys reveal an unexpected scarcity of primary vector mosquitoes in a region of persistent malaria transmission in western Zambia

Abstract Background The Barotse floodplains of the upper Zambezi River and its tributaries are a highly dynamic environment, with seasonal flooding transhumance presenting shifting mosaic potential larval habitat human livestock blood meals for malaria vector mosquitoes. However, limited entomological surveillance has been undertaken to characterize community in these their environs. Such information is necessary as, despite substantial deployment insecticide-treated nets (ITNs) indoor residual spraying (IRS) against Anopheles vectors, transmission persists across Barotseland Zambia’s Western Province. Methods Geographically extensive surveys were two health districts along 102 km transects, at fine spatial resolution, during dry season following peak successive wet season. Larvae sampled within typical flight range settlements identified through genetic sequencing cytochrome c oxidase I internal transcribed spacer regions mitochondrial nuclear DNA. This facilitated detailed comparison taxon-specific abundance patterns between ecological zones differentiated by hydrological controls. Results An unexpected paucity primary vectors was revealed, An. gambiae s.l. funestus representing < 2% 995 sequenced anophelines. Potential secondary predominated community, primarily coustani group species squamosus. While distribution study area clustered, ubiquitous landscape both seasons, some relationships Conclusions diversity candidate high relative observed diverse hydro-ecosystems indicate adaptable system, resilient environmental variation and, potentially, interventions that target only part community. Larval survey results imply being mediated predominantly species, whose known tendencies crepuscular outdoor biting renders them largely insensitive prevalent control methods. Graphical