Bio-Efficacy Studies of Bt and Non-Bt Cotton against Field Collected Pink Bollworm (Pectinophora gossypiella) Larvae

Cotton (Gossypium spp.) is a crucial global cash crop, but its production is severely impacted by insect pests, particularly the pink bollworm (Pectinophora gossypiell). Pink bollworm has developed resistance to Bt toxin under increased selection pressure. The present study on bio-efficacy of Bt and non-Bt cotton against field-collected pink bollworm larvae was conducted at Agricultural Research Station, Dharwad India during 2021 November - 2023 January under laboratory conditions using Jadoo BG II and Jadoo non-Bt (Kaveri Seeds) as Bt and non-Bt cotton respectively. Second instar larvae were exposed to seed bits from both cotton types at 120 and 150 days after sowing. Mortality rates were recorded at 12-hour intervals for 72 hours. Results showed consistently higher mortality in Bt cotton compared to non-Bt cotton with maximum corrected mortality of 29.61% for Bt cotton at 72 hours. Linear regression analysis revealed a strong positive correlation between time and mortality rates for both cotton types. Area Under the Curve analysis and relative effectiveness calculations further confirmed the superior performance of Bt cotton. However, there was a decreasing trend in mortality from 120 to 150 days after sowing indicating temporal variation in insecticidal gene activity. The study emphasizes that while Bt cotton remains effective against pink bollworm, integrated pest management strategies are needed along with more research into temporal variations in toxin efficacy.