Evaluation of insecticide resistance and biochemical mechanisms in Anopheles stephensi from Punjab, Pakistan

Though Anopheles stephensi is a predominant malaria vector in rural and urban areas, mosquito control largely relies upon indoor residual spraying by pyrethroids in Pakistan. Therefore, identification of factors inducing mosquito susceptibility to insecticides and deciphering resistance mechanisms are key steps for integrated vector control interventions. Here, we determine susceptibility of An. stephensi to pyrethroids, carbamates and organochlorine insecticides at various localities in districts Kasur and Shiekhupura of Punjab province. Percentage mortality, KDT₅₀ and KDT₉₅ were measured as per WHO criteria and probit log model. Variations in quantity or activity of different enzymes involved in insecticide detoxification from the same families of mosquitoes were also detected through biochemical assays. Although we found An. stephensi susceptible to permethrin, a high level of resistance was detected against bendiocarb, DDT and deltamethrin in both districts. Biochemical assays, compared to susceptible strains of An. Stephensi, showed significant elevation in activity of non-specific esterases (NSEs), Gluthatione S transferase (GST) and mixed function oxidases (MFOs) along with altered target site activity of acetylcholinestrase (AChE) in field strains of mosquitoes. Results concludes emergence of multiple insecticide resistance in An. stephensithat could be a potential threat to public health in endemic areas of Punjab, Pakistan. An effective long term integrated resistance management strategy is needed to facilitate selection of insecticides and subsequent efficacy of existing chemicals.

Key words: Anopheles stephensi, Malaria, Public health, Mosquito control, Susceptibility to insecticides