Larvae density, breeding habitat preference and insecticide susceptibility status of Anopheles gambiae (Diptera: Culicidae) in Assosa district, western Ethiopia

Abstract

Background Malaria vectors control interventions mainly rely on the control of adults using indoor residual sprayings and long-lasting insecticidal nets in Ethiopia. However, the emergence and widespread of insecticide resistance in the primary malaria vector, Anopheles gambiae sinso lato challenges the malaria vector control efforts in Ethiopia. The aim of this study was to investigate species composition, abundance and insecticide resistance status of main malaria mosquitoes in Assosa district, Benishangul Gumuz, Western Ethiopia. Methods The study was conducted from July 2021 to June 2022. After identification of possible breeding sites, Anopheles mosquito larvae were collected using a standard dipper from varies breeding habitats. Susceptibility tests were conducted on wild population of female An. gambiae complex following World health organization standard susceptibility test procedure. Insecticide impregnated papers with deltamethrin (0.05%), alphacypermethrine (0.05%), propoxur (0.1%), and primiphos methyl (0.25%), were used for the study. Result Six major Anopheles mosquitoes’ larvae breeding habitats were identified in four villages, namely, drainage ditch, swamp, pond, animal footprint, sewerage and stagnant water. A total of 2051 Anopheles larvae were collected and identified. Out of all collected Anopheles larvae, 1884 larvae were reared and identified to four species (An. gambiae s.l., An. coustani, An. ziemanni and An. funestus). An. gambiae s.l. were found to be the dominant species (1732, 84.4%) species and the lowest An. funestus were collected (n = 17, 0.9%). The most productive habitats were stagnant water (n = 752; 39. 9%) with larvae/dip while sewerage were detected to be least productive (n = 71; 3.76%) for Anopheles mosquito larvae with mean density of 1.2 and 0.03 larvae/dip, respectively, (P < 0.05). The susceptibility result indicated that the population of An. gambiae s.l in the study area found resistant against alphacypermethrine, deltamethrin and permethrin 63%, 71% and 43% respectively. The result revealed that the vector is susceptible to pirimiphos-methyl and propoxur with 100% susceptibility rate. Conclusion Anopheles gambiae complex is the predominant malaria vector in Assosa District. Anopheles gambiae complex developed high level of resistance against most of insecticide classes. Pirmiphosmethyl and propoxur are effective insecticides for malaria vector control in Assosa district, Ethiopia.