Laboratory Evaluation of Some Insecticides Against Cotton Leafworm, Spodoptera littoralis (Boisd) (Lepidoptera: Noctuidae).

The toxicological effects of some insecticide mixtures             (chlorpyrifos, pyridalyl, chlorantraniliprole, emamectin benzoate, and methoxyfenozide), against the 3^rd instar of Spodoptera larvae were evaluated.
            The results indicated that, LC₅₀ values for each insecticide were 12.44, 0.88, 0.08, 0.16 and 3.35 mg L^-1 respectively, and 0.458, 0.009, 0.0014 and 0.357 mg L^-1 respectively.Also, the LC₅₀ values of chlorpyrifos are increased by larvae weight increased. LC₅₀ values of chlorpyrifos as a function of post-feeding initiation of Spodoptera larvae to pyridalyl, chlorantraniliprole, emamectin benzoate, and methoxyfenozide after two days (single exposure) were 1.33, 1.99, 0.74, and 0.37 mg L^-1 respectively.
            Therefore, post-feeding initiation of larvae to previous insecticides tremendously decreased LC₅₀ values of chlorpyrifos.Also, the percent inhibition of AChE from Spodoptera head capsules by chlorpyrifos, pyridalyl, chlorantraniliprole, emamectin benzoate, and methoxyfenozide (LC₁₀ equivalent concentrations) were 44.5, 23.4, 19.4, 33.5, and 15.4%, respectively.
            The percent inhibition of AChE from Spodoptera head capsules by chlorpyrifos either pre-treatment or post-treatment with pyridalyl, chlorantraniliprole, emamectin benzoate, and methoxyfenozide were increased. This indicates that the toxic potential of these pesticides for the tested organism is greater when present in a mixture than in an individual.