Effect of simulated rains on persistent toxicity of endosulfan and monocrotophos to gram pod borer, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on gram crop1

The influence of simulated rains of 0, 2, 6, and 10 mm levels on persistent toxicity of endosulfan and monocrotophos @ 0.07 and 0.04 per cent respectively, against the gram pod borer, Helicoverpa armigera (Hubner) on the chickpea variety ‘H-208’ was studied in the screen house. The simulated rains were done at 0, 4, 8, 12, 24 and 48 h intervals after the insecticidal spray with the knapsack sprayer fitted with adjustable nozzle. Ten, 1 to 2-day old larvae reared on artificial diet were released on treated gram twigs kept in specimen tubes and mortality was observed 24 h after the exposure. The persistent toxicity was determined 0, 1, 3, 5, 7 and 10 days after the spray. A trend of reduction in persistent toxicity (PT) with the increase in rain level was observed. The rains of different levels occurring at 0 h after the insecticidal spray drastically reduced the persistent toxicity as compared to other rain intervals. PT of monocrotophos was found to be higher than endosulfan at all the rain levels and at all the rain intervals and at the same time change in PT was gradual in monocrotophos compared to endosulfan. Increase in PT was observed in endosulfan and monocrotophos upto 12 and 8 h after the spray, respectively and thereafter it started decreasing.