UTTAR PRADESH JOURNAL OF ZOOLOGY

The Bihar hairy caterpillar, Spilosoma obliqua (Walker), is a major defoliator of several crops including blackgram, green gram, castor, sunflower, mustard, jute and mulberry. A laboratory bioassay was conducted during 2024 and September, 2025 using the surface diet contamination method to evaluate the toxicity and speed of kill.  Probit analysis revealed significant variation in toxicity among insecticide groups tested. The sodium channel modulator i.e. Cypermethrin 25 EC has recorded the lowest LC₅₀ (23.89 ppm), showing it as the best insecticide for the management of S. obliqua and this was followed by ryanodine receptor modulators like Chlorantraniliprole 18.5 SC, Cyantraniliprole 10OD and nAChR allosteric modulator i.e. Spinosad 45 SC. While Flubendiamide 39.35 SC (640.75 ppm) was the least effective, followed by Quinalphos 25 EC and Tetraniliprole 18.18 SC. Further, LT₅₀ values of the above 7 insecticides varied from 1.80 to 7.23 days. Cypermethrin 25 EC has the fastest knockdown effect with the lowest LT₅₀ (1.8 days), followed by Spinosad, Tetraniliprole 18.18 SC and Quinalphos 25 EC (3.74). Among diamides, Tetraniliprole, Cyantraniliprole and Chlorantraniliprole exhibited quicker action than Flubendiamide (7.23 days). Cypermethrin 25 EC was identified as most effective insecticide for S. obliqua management by considering both toxicity and speed of kill.  This was followed by Spinosad 45 SC, Chlorantraniliprole 18.5 SC and Cyantraniliprole 10 OD. Thus 3 different modes of action insecticides are identified for inclusion in IPM programmes for sustainable management of S. obliqua without insecticide resistance development.