Seasonal dynamics, resting behaviour and insecticide susceptibility of Anopheles mosquitoes across two differentially malaria-endemic regions in Ethiopia

Abstract

Information on bionomics of Anopheles species composition, seasonal dynamics and insecticide susceptibility status is important to understand malaria transmission in any particular eco-epidemiological setting and for the design of effective vector control strategies. Here, adult mosquitoes were collected using CDC light traps (CDC LTs) and human landing catches (HLC) for 17 months between June 2018 and September 2020 from Lare District of Ethiopia. Larvae and pupae of anopheline mosquitoes were collected from breeding sites of Lare District and Jimma and reared to adulthood. Bioassays were conducted on non-blood-fed, 3–5-day-old emerged adult female mosquitoes using WHO insecticide-impregnated papers. Plasmodium spp. infection in Anopheles pharoensis and An. coustani were identified using TaqMan qPCR. Of 11,048 Anopheles mosquitoes collected, An. coustani was the most common (46.20%, n = 5103), followed by An. pharoensis (27.89%, n = 3082), An. gambiae (s.l.) (16.04%, n = 1772) and An. funestus (9.88%, n = 1091). Most of the mosquitoes (73.17%, n = 8084) were collected using CDC LTs and 26.83% (n = 2964) were captured using HLC. The mean density of An. gambiae, An. pharoensis and An. coustani was generally higher in June-November as compared to other months during the study period. However, the mean density of An. funestus was relatively higher through November-January following the peak malaria period in Lare. Anopheles pharoensis, An. gambiae (s.l.) and An. coustani complex were susceptible to pirimiphos-methyl, propoxur and bendiocarb. However, An. pharoensis and An. gambiae (s.l.) were resistant to DDT, deltamethrin, permethrin and malathion, whilst members of the An. coustani complex were resistant to DDT and deltamethrin. No Plasmodium spp. infection was detected from samples of Anopheles coustani and An. pharoensis. There was temporal variation in mean density of Anopheles mosquitoes and higher mean mosquito density was recorded during June-November (except for An. funestus). The higher outdoor mean mosquito density coupled with multiple insecticide resistance of malaria vector populations and occurrence of An. funestus in the dry season call for regular monitoring and intervention considering the behavioural dynamics of Anopheles species across seasons.