Current status of Anopheles stephensi response to various insecticides in some areas of the Thar desert

Investigations on the current response of A. stephensi. to six insecticides viz. DDT, dieldrin, malathion, fenitrothion, propoxur and permethrin, were carried out in 3 districts i.e. Barmer, Jodhpur and Pali, of the Thar desert. The species was found resistant to DDT and dieldrin, partially resistant to malathion and susceptible to fenitrothion, propoxur and permethrin. Dieldrin and malathion resistance has been detected for the first time in the Thar desert. Lethal concentrations (LC50 & LC95) of DDT and dieldrin and lethal exposure times (LT50 & LT95) of malathion, fenitrothion, propoxur and permethrin have been determined. In some areas, the differences in LC50 and LT50 values of tested insecticides, except fenitrothion, were found statistically significant. Chi-square and regression tests have revealed the homogeniety and linear trend respectively in the response of A. stephensi to insecticides. The findings of the study indicate that organochlorine compounds can be used alternately in the spray operations.