Influence of host plants on the susceptibility of Spodoptera litura (Fabricius) to insecticides

Studies were conducted to assess the variable susceptibility of Spodoptera litura Fabricius reared on soybean and cabbage to five insecticides viz., cypermethrin + chlorpyriphos, cypermethrin + profenophos, cypermethrin, chlorpyriphos and profenophos by topical application method. The larvae of S. litura reared on cabbage recorded the lower LD₅₀ values in the range of 0.4885 to 0.9258 μg a.i./larva to all insecticides compared to soybean (0.4405 to 0.7909 μg a.i./larva). Irrespective of host plants, high frequency of resistance was recorded to cypermethrin (0.9258 and 0.7909 μg a.i./larva) followed by profenophos (0.8212 and 0.7598 μg a.i./larva), chlorpyriphos (0.5352 and 0.5225 μg a.i./larva), cypermethrin + profenophos (0.5133 and 0.4597 μg a.i./larva) and cypermethrin + chlorpyriphos (0.4885 and 0.4404 μg a.i./larva) in cabbage and soybean, respectively. The results indicated that the field population of S. litura reared on soybean was susceptible to mixed and single insecticides as compared to those reared on cabbage by relative effectiveness of 1.11, 1.12, 1.17, 1.02 and 1.08 times to cypermethrin + chlorpyriphos, cypermethrin + profenophos, cypermethrin, chlorpyriphos and profenophos, respectively.