Relative Toxicity of Some Synthetic Insecticides against Different Populations of Spodoptera litura (Fabricius)

The relative susceptibility of three populations of Spodoptera litura to certain novel insecticides along with conventional was determined. Among the novel insecticides tested, indoxacarb was found be the best against Bangalore and Guntur population with higher relative toxicity than cypermethrin (12.1 and 15.9), fenvalarate (10.9 and 20.6) γ-cyhalothrin (6.1 and 26.0) and profenophos (9.2 and 20.4), respectively, to which the pest has developed increased level of resistance followed by emamectin benzoate which was 6.0 and 4.2, 5.5 and 5.48, 3.1 and 6.92 and 4.58 and 5.44 times toxic than cypermethrin, fenvalarate γ-cyhalothrin and profenophos at LC₅₀ level. Where as selel population was most susceptible to emamectin benzoate with 3.2, 9.0, 3.1, 18.9 and 1.5 times more toxic than cypermethrin, fenvalarate, γ-cyhalothrin, profenophos and indoxacarb. Also, the larvae of S. litura obtained from Guntur and Bangalore was 10.4, 4.8, 17.2 and 7.8 fold and 3.6, 1.1, 1.8 and 1.9 fold resistance to cypermethrin, fenvalarate, γ-cyhalothrin, and emamectin benzoate, respectively, as compared to Delhi population. Thus, the values of relative toxicity of new synthetic molecules with diversified mode of action can be looked upon as a ready reckoner and would form the basis for the selection of insecticide as one of the component of pest management tactics.