Susceptibility of Dengue/ Chikungunya vector, Aedes aegypti against carbamate, organochlorine, organophosphate and pyrethroid insecticides

Aim : Controlling vectors through source reduction measures and larviciding and fogging operation with insecticides are being carried out by the state health department during outbreak period. The present study was conducted to understand the susceptibility status of dengue vector Aedes aegypti (Linnaeus, 1762) field strain towards various insecticides as a base line data. Methodology : Twenty five adult females of Ae. aegypti were exposed to organochlorine and organophosphate insecticide for 30 and 60 min and exposure duration of pyrethroid compounds for 5 and 15 min with four replicates for respective insecticides as experiment and a separate control was also maintained. The percentage mortality count was made 24 hrs after the exposure and data were pooled to determine the level of resistance / susceptibility status. Results : Ae. aegyptifemales were exposed to 0.1% carbamate propoxur for 30 and 60 min and the observed mortality after 24hrs was 96% and 100%. Similarly, exposure to 0.4% Dieldrin resulted in 48% and 100% mortality whereas 4% Dieldrin for the same duration recorded 88% and 100% morality. Exposure to 0.1% Fenitrothion for the same period led to 40.0% and 100% mortality, whereas 5.0 %Malathion, exposure recorded 28% and 100% mortality respectively.Atotal of five different pyrethroid compounds include Cyfluthrin (0.15% and 0.5%), Deltamethrin (0.05%), Etofenprox (0.5%) Lambda Cyhalothrin (0.05%) and Permethrin (0.75%) were tested for exposure duration of 5 and 15 min against Ae. aegypti. Based on the mortality after 24 hrs the efficacy of insecticides for 5 min exposure was in the following order Lambdacyhalothrin> Cyfluthrin > Deltamethrin > Permethrin and > Etofenprox, whereas exposure for 15 minutes the order was Cyfluthrin > Permethrin > Deltamethrin > Lambdacyhalothrin and >Etofenprox, respectively. Interpretation : Ae.aegypti was found to be relatively less susceptible to organophosphorous compounds, however, they were found invariably susceptible to all tested pyrethroid compounds. The data suggests that utilization of various insecticides in this region has been minimal for past several decades and fogging operations of insecticides are intensified during the outbreak period of dengue or chikungunya. The present study will form a baseline for initiating in depth studies on molecular and biochemical enzyme activities.