Autosomal inheritance of alphamethrin, a synthetic pyrethroid, resistance in Anopheles stephensi – Liston, a malaria mosquito

Abstract

Anopheles stephensi–Liston (Culicidae: Diptera) is an important urban malarial vector in the Indian sub-continent, accounting for about 15% of the total annual malaria incidence. Chemical control represents a key strategy in the management of this insect vector. However, owing to erratic and continuous application of insecticides, resistance has become a common phenomenon among them and their control has become an uphill task. The genetics of alphamethrin, a synthetic pyrethroid resistance was studied to determine its mode of inheritance. The late third instar larvae were selectively inbred for 27 and ten generations to synthesize homozygous resistant (R) and susceptible (S) stocks, respectively, to the diagnostic dose of 0.12 mg l−1. The log-dosage probit mortality relationships and degree of dominance (D) were calculated. Resistance was observed in both sexes, the dosage-mortality (d-m) line of F 1 was towards the resistant parent and the ‘D’ value was found to be 0.8 indicating alphamethrin resistant (amr) gene to be autosomal and incompletely dominant. The d-m lines of F 2/backcross exhibited a clear plateau of mortality across a range of doses indicating monogenic resistance. The null hypothesis for monogenic resistance was tested from mortality data of backcross progeny compared with theoretical expectations using the χ2 test and was found to be non-significant. Understanding genetics of insecticide resistance is significant in prediction and management of resistant insects. The amr genes can be used as genetic marker in A. stephensi, which can be used in several applications in conducting basic and applied genetic research.