Persistence and residual toxicity of some insecticides against Aphis gossypii (Glov.) on okra leaves

The persistence and residual toxicity of carbaryl, endosulfan, malathion and monocrotophos at recommended concentrations, viz., 0.1, 0.07, 0.08 and 0.05 per cent, respectively, were evaluated against the second instar nymphs of Aphis gossypii (Glov.). The PT values for carbaryl, endosulfan, malathion and monocrotophos were 446.32, 426.38, 191.02 and 970.26 during the first season and 512.98, 459.54, 217.65 and 1002.10 during the second season, respectively. Evidently, monocrotophos was the most effective insecticide followed by carbaryl, endosulfan and malathion against A. gossypii. Monocrotophos exhibited the maximum residual toxicity followed by carbaryl, endosulfan and malathion, the LT50 values during the first season being 5.8, 2.4, 1.97 and 0.61 days; and 5.8, 4.7, 2.8 and 1.1 days, respectively in the second season.