Bioefficacy of some insecticides and mixed formulations against Spodoptera litura (Fab.)

The bioefficacy of fenpyroximate, fenvalerate, ethion + cypermethrin and thiamethoxam + lambda-cyhalothrin was determined against 5d old larvae of S. litura (mean larval wt. = 0.0232 g) by atomization method. Ethion + cypermethrin was most toxic at 12 (LC₅₀ = 0.0074%), fenpyroximate at 24 (LC50 = 0.00667%) and thiamethoxam + lambda-cyhalothrin at 48 hours after exposure (LC50 = 0.0067%). The same insecticides/combinations did not prove to be the ‘most toxic ’at all the four exposure periods i.e. 12, 24, 48 and 72 HAE. For example ethion + cypermethrin were most toxic at 12, fenpyroximate at 24, thiamethoxam + lambda-cyhalothrin at 48 and ethion + cypermethrin again at 72 HAE. Fenvalerate (0.01 and 0.009%) caused 50% mortality in 3.77 and 5.46 h; fenpyroximate (0.01, 0.009 and 0.008%) in 2.93, 4.38 and 7.29 h and thiamethoxam + lambda-cyhalothrin (0.009%) in 12.97 h, respectively.