Relative potency of insecticides against field populations of fall armyworm in Marathwada region of Maharashtra

A bioassay study was conducted to evaluate the relative potency of selected insecticides against field populations of fall armyworm, S. frugiperda (J.E. Smith), collected from three districts of Marathwada, Maharashtra, namely Chhatrapati Sambhajinagar, Parbhani, and Latur. Second instar larvae of the F₁ generation were tested by the leaf-dip method at five concentrations of each insecticide. Median lethal concentrations (LC₅₀) were estimated by probit analysis, and relative potency was calculated against the least effective compound. Significant variation in toxicity was observed among insecticides. Emamectin benzoate 5 SG consistently showed the lowest LC₅₀ values (0.027-0.041 g/L) and the highest relative potency (360.88-1597.70), confirming its superior efficacy. Chlorantraniliprole 18.5 SC and spinetoram 11.7 SC also performed well, with LC₅₀ values ranging from 0.057 to 0.121 ml/L and relative potency between 264.21 and 615.24. By contrast, lambda-cyhalothrin 5 EC recorded very low potency (RP = 4.07-7.57), while flubendiamide 20 WG consistently showed the highest LC₅₀ values (14.80-43.14 g/L) and served as the baseline (RP = 1.00). The results demonstrate that emamectin benzoate is the most effective insecticide for managing S. frugiperda in Marathwada, with chlorantraniliprole and spinetoram as suitable alternatives. Lambda-cyhalothrin and flubendiamide were least effective.