Insecticide resistance in Aedes aegypti and Aedes albopictus in southern Benin: quantification, investigation of kdr mutations, and detection of detoxification enzyme activity

Abstract Background Insecticide resistance in arbovirus vectors threatens the effectiveness of vector control strategies in many endemic regions. Understanding resistance profiles and identifying underlying mechanisms are essential for preventing operational failures. This study assessed the susceptibility of Aedes aegypti and Aedes albopictus to commonly used insecticides in southern Benin and investigated the contribution of knockdown resistance mutations and metabolic detoxification pathways. Methods Entomological surveillance was conducted in Lokossa, Bohicon, and Dassa, where ovitraps were used to collect eggs of Aedes species. Eggs were reared to the adult stage under controlled insectary conditions. Nonblood-fed females aged 2–5 days were tested using standard tube assays to determine susceptibility to deltamethrin at 0.05%, permethrin at 0.75%, and bendiocarb at 0.1%. Additional concentrations at fivefold and tenfold the diagnostic doses were used to measure resistance intensity. Polymerase chain reaction assays were performed to detect mutations in the voltage-gated sodium channel gene associated with knockdown resistance. Biochemical assays were conducted to quantify the activity of oxidases, glutathione-S-transferases, and esterases. Exact binomial tests were used to compute confidence intervals for mortality rates and allele frequencies. Results Aedes aegypti populations from the three communities showed resistance to deltamethrin and permethrin at the diagnostic dose while remaining fully susceptible to bendiocarb. Mortality increased substantially at elevated concentrations, indicating moderate resistance intensity. Aedes albopictus populations were fully susceptible to all tested insecticides. Three mutations in the voltage-gated sodium channel gene, F1534C, V1016G, and S989P, were identified in Aedes aegypti with allele frequencies ranging between 33.89% and 46.67%. Biochemical assays revealed elevated oxidase activity in all Aedes aegypti populations, with increased levels of glutathione-S-transferases and both alpha- and beta-esterases in Bohicon and Lokossa. Conclusions The study documents pyrethroid resistance in Aedes aegypti from southern Benin, while Aedes albopictus remains susceptible. Both species showed high susceptibility to bendiocarb. The presence of three knockdown resistance mutations at moderate frequencies together with increased detoxification enzyme activity indicates that both target-site and metabolic mechanisms contribute to resistance development. These findings underscore the need for integrated resistance management to preserve the effectiveness of insecticidal interventions.