Toxicity of Steward (Indoxacarb) Against Cotton Bollworm, Helicoverpa armigera (Hub.)

Various concentrations of Steward 150 SC, indoxacarb viz., 50, 100, 200, 300 and 500 ppm were tested against different larval instars of cotton bollworm, Helicoverpa armigera (Hub.) to determine its toxicity range under controlled laboratory conditions. Percent mortality of the insect was recorded after 12, 24, and 48 hours exposure to insecticide. The results showed that mortality of second instars varied significantly in between treatments after 12 hours but non-significantly with cent per cent mortality after 24 and 48 hours. Third and fourth instars exhibited variable mortality range after 12, 24 and 48 hours. It was 46-73%, 47-80% and 13-1 00% in third instar and 33%, 13-40% and 20-100% in fourth instar after 12, 24 and 48 hours respectively. The overall results conclude that fourth instars are more resistant to insecticide at all concentrations than third and second instars.