22 Eyl 2025 Pazartesi
Reduced pyrethroid morbidity and resistance of jointly exposed Anopheles and Culex mosquitoes: Implications for malaria-lymphatic filariasis co-intervention plans
Abstract : Emerging adult Anopheles and Culex mosquitoes migrate to human dwellings, at great risks of insecticide exposure, in search of bloodmeal. Countries like Nigeria, targeting this joint mosquito host-seeking behaviour have launched Malaria-Lymphatic Filariasis (Malaria-LF) co-intervention plans using synergistic insecticide-based control tools. However, insecticide resistance currently threatens mosquito vector control. This study investigated separate and combined pyrethroid insecticide exposure response of Anopheles gambiae sensu lato (s.l.) and Culex pipiens complex mosquitoes collected from two mixed breeding sites in Nigeria. Adult Anopheles and Culex mosquitoes reared from larval collections were exposed in separate and joint insecticide susceptibility tests to permethrin 0.75%, deltamethrin 0.05% and alphacypermethrin (0.05%) using World Health Organization (WHO) kits. The mosquitoes were identified morphologically. Time to mosquito knockdown, percentage knockdown, and mortality were monitored. The results for the different mosquito and exposure types were compared. Both mosquitoes were resistant to all pyrethroid insecticides tested. Significantly higher Anopheles knockdown was recorded compared to Culex for the joint (Anopheles 79-89% vs Culex 44-50%, P ≤ 0.011) and separate (Anopheles 67-88% vs Culex 46-47%, P < 0.048) exposures respectively. Time to 95% Anopheles and Culex mosquito knock down were shorter during separate (2200.9 mins) than in joint (4513.9 mins) exposures. Faster Anopheles knockdown (kdt50 18.7 - 68.8 mins) were recorded compared to Culex (kdt50 22.1 - 98.8 mins). Higher but not significantly different (P ≥ 0.083) mosquito mortalities were recorded from separate than in joint Anopheles and Culex exposures. There were no significant (P ≥ 0.072) differences between Anopheles 43-77% and Culex 41-72% mortalities for separate and joint exposures. The speed of action and morbidity effects of the pyrethroid insecticides tested were lower during joint than in the separate mosquito exposures. Taken together, reduced pyrethroid speed of action and morbidity along with multiple mosquito resistance noted could threaten insecticide user-acceptability, performance perception and Malaria-LF co-intervention in the field.