Biochemical characterization of insecticide resistance in field population of major JE vectors from northern districts of West Bengal, India

Regular monitoring of insecticide resistance among vector mosquitoes and their mechanism are very important for formulation of effective vector control measures. Insecticide resistance developed due to metabolic resistance which is mediated by the enhanced production of different detoxifying enzymes resulting in sequestration or biodegradation of insecticides. Present study was designed to assess any evidence of metabolic resistance among four major JE vectors - Cx. tritaeniorhynchus, Cx. vishnui, Cx. pseudovishnui , and Cx. gelidus from northern districts of West Bengal, India. A total of 92 adults per species of JE vectors in each study districts were analysed to measure the activity/levels of acetylcholinesterase (AChE), non-specific esterase (ESTs), glutathione-S-transferases (GSTs), and cytochrome P450s mono-oxygenase (CytP450s) according to WHO protocol. A significant increase in mean AChE activity without propoxur were observed among most of the JE vector species. All four species showed significantly elevated AChE activity with propoxur, except Cx. gelidus of Darjeeling and Uttar Dinajpur. More than 70% of Cx. tritaeniorhynchus showed homozygous resistant (RR) genotype to propoxur-inhibited residual activity of AChE but Cx. gelidus , Cx. pseudovishnui and Cx. vishnui showed either homozygous sensitive (SS) or heterozygous resistant (RS) genotype. More than 50% and 80% population of all species showed an elevated level of both alpha, beta ESTs and GSTs. CytP450s activity was also higher among all species. The present study suggests that the development of resistance against different classes of insecticides among four major JE vector species is becoming a matter of concern that should be monitored closely.