Baseline Toxicity of Insecticides against Tobacco Caterpillar, Spodoptera litura (Fabricius)

Third instar laboratory reared (11^th generation) and field collected larvae of Spodoptera litura (3^rd instar) were exposed to seven different insecticides using leaf dip bioassay to estimate the baseline toxicity. The percent baseline susceptibility values for fenvalerate, chlorpyriphos, acephate, thiodicarb, indoxacarb, pyridalyl and chlorantraniliprole were 0.016, 0.00097, 0.00979, 0.00035, 0.0000116, 0.0001129 and 0.000000238. Chlorantraniliprole was the most toxic recording the respective LC₅₀ values of 0.0000005 and 0.000000238 followed by indoxacarb (0.0000132 and 0.0000116%) in the F₁ and F₁₁ generations of the field collected population. The susceptibility index was worked out to be 2.50, 5.25, 1.84, 2.86, 1.14, 8.22 and 2.10 for fenvalerate, chlorpyriphos, acephate, thiodicarb, indoxacarb, pyridalyl and chlorantraniliprole, respectively. The LC₅₀ for the susceptible strain was used for monitoring the insecticide resistance in field population.