Resistance to organophosphate and pyrethroid and their underlying mechanism in Aedes albopictus (Diptera: Culicidae) from dengue endemic sub-Himalayan West Bengal, India.

Dengue cases are increasing every year in the sub-Himalayan part of West Bengal, where Aedes albopictus (Skuse 1894) has emerged as a predominant dengue vector. Dengue management heavily relies on the recurrent application of chemical insecticides such as temephos (larvicide) and deltamethrin (adulticide). However Ae. albopictus can quickly develop resistance which complicates their management. Thus, detailed population-specific studies on resistance status and mechanism of resistance are useful for designing an effective dengue management strategy. In this study, wild mosquitoes were collected and bioassays with temephos and deltamethrin, including synergist assays, were conducted to investigate the probable mechanism of resistance. Furthermore, carboxylesterase activity and level of monooxygenase were measured followed by real-time polymerase chain reaction analysis to assess expression patterns of CCE and CYP genes. Bioassays confirmed temephos and deltamethrin resistance in Ae. albopictus population is driven by metabolic detoxification. Biochemical assay recorded significantly elevated carboxylesterase activity and monooxygenase levels compared to a susceptible laboratory strain. This is further supported by the elevated relative expression of CCE and CYP genes with consistent expression of CYP6A8 and CCEae3a in these populations. A molecular docking study suggested that the conformation of the binding site for temephos and deltamethrin may enhance their potential metabolism. These findings align with the global trend of insecticide resistance development and highlight the urgent need for more sustainable and informed approaches to dengue vector management.