Toxicity of Certain Insecticides Against Different Stages of Cotton leafworm, Spodoptera littoralis (Boisd.)

The current study investigated the toxicity of five insecticides, indoxacarb, thiamethoxam+chlorantraniliprole, chlorantraniliprole, fipronil and lufenuron against the 2nd and the 4th instar larvae of the cotton leafworm, Spodoptera littoralis using leaf-dip bioassay under laboratory conditions. Based on the LC50s values of the tested insecticides for the 2nd instar larvae of S. littoralis, the most toxic insecticide was indoxacarb (0.009, 0.006 and 0.001 ppm), followed by thiamethoxam + chlorantraniliprole (0.016, 0.01 and 0.009 ppm fold), chlorantraniliprole (0.21, 0.12 and 0.052 ppm fold), fipronil (3.79, 2.81 and 0.661 ppm fold) and lufenuron (5.19, 3.21 and 0.916 ppm fold) after 24, 48 and 72 hrs. post exposure, respectively. The toxicity index and relative potency values showed indoxacarb was more toxic for the 2nd instar larvae than thiamethoxam + chlorantraniliprole, chlorantraniliprole, fipronil and lufenuron by (1.78, 23.33, 421.11 and 576.67), (1.67, 20.00, 468.33 and 535.0) and (9.0, 52.0, 661.0 and 916.0) fold, respectively. The 4th instar larvae showed high susceptibility to indoxacarb compared thiamethoxam + chlorantraniliprole, chlorantraniliprole, fipronil and lufenuron. The LC50s values of the tested insecticides revealed that indoxacarb was more effective than other insecticides (0.83, 0.61 and 0.32 ppm), followed by thiamethoxam + chlorantraniliprole (7.11, 5.23 and 1.11 ppm), fipronil (10.11, 9.13 and 3.26 ppm) and lufenuron (16.38, 14.39 and 4.11 ppm) after 24, 48 and 72 hrs. exposure, respectively. Therefore, our study recommended using indoxacarb, thiamethoxam + chlorantraniliprole and chlorantraniliprole in controlling CLW because of their mode of action are different and promising for using these insecticides in Integrated Pest Management programs.