Dose response assessment of selected insecticides against Aphis gossypii Glover infesting Bt cotton under laboratory condition

The cotton aphid (Aphis gossypii Glover) has emerged as major sucking pest in Bt cotton, exhibiting resistance to diverse chemical classes.This study evaluated the dose-response toxicity of eight insecticides against A. gossypii nymphs using the leaf-dip bioassay method under laboratory conditions.Mortality was recorded at 72 hours post-treatment and analysed using probit analysis.Based on median lethal concentration (LC ) values, toxicity followed the descending order: acetamiprid 20 SP (0.002%) > 50 thiamethoxam 25 WG (0.004%) > fipronil 5 SC (0.005%) > clothianidin 50 WDG (0.006%) > flonicamid 50 WG (0.007%) > tolfenpyrad 15 EC (0.020%) > diafenthiuron 50 WP (0.037%) > afidopyropen 50 g/L DC (0.051%).Acetamiprid 20 SP exhibited the highest insecticidal toxicity with a toxicity level 25.50 fold greater than that of afidopyropen 50 g/L DC, the list toxic insecticide evaluated.These baseline toxicological findings provide essential insights for designing rotational chemical strategies and effective management of insecticides resistance in Bt cotton ecosystems.