Susceptibility status of Aedes aegypti (L.) (Diptera: Culicidae) to temephos from three districts of Tamil Nadu, India.

BACKGROUND & OBJECTIVES Dengue is the most rapidly expanding arboviral disease in India. Aedes aegypti is the primary vector of dengue fever. Chemical insecticides have long been used in the vector control programmes along with other control measures. However, continuous use of insecticides targeting Ae. aegypti may lead to development of insecticide resistance. Though resistance in Ae. aegypti has been reported, the mutation in ace-1 gene associated with temephos resistance is not reported in natural populations. The present study aims to evaluate the susceptibility/resistance status of Ae. aegypti to temephos from three districts of Tamil Nadu. METHODS Ae. aegypti larvae were sampled from different locations in three districts, viz., Dharmapuri, Salem and Namakkal. The standard WHO larval bioassay, biochemical assays and spotting of specific mutation (G119S) in the acetylcholinesterase gene, which is associated with organophosphate resistance, were carried out by PCR and sequencing. RESULTS The results showed that larvae from Namakkal (NKL) population had an alteration in their susceptibility status (RR = 6.9 fold), while the other populations were moderately susceptible to insecticides. Biochemical assay showed increased activity for α- and β-esterase in NKL, as well as evidence of acetylcholinesterase insensitivity. G119S mutation was detected in this population with high frequency of 0.24. INTERPRETATION & CONCLUSION The high activity of esterase, mixed-function oxidase (MFO) and ace-1 mutation frequency were closely associated with temephos resistance. Early detection of resistance alleles in natural vector population could be useful for the successful implementation of insecticide resistance management strategies. The results of this study provide baseline data on temephos resistance in Ae. aegypti populations.