Status of Bio-efficacy of Imidacloprid against Red Cotton Bug, Dysdercus cingulatus Fab. (Hemiptera: Pyrrhocoridae) by Leaf Dip and Seed Soaking Method

Imidacloprid was tested against redcotton bug by seed soaking and leaf dip method. The dosage regime of the imidacloprid selected for the study was:-3000, 2500, 1250 and 500 ppm for seed soaking and leaf dip methods both. At 12h exposure imidacloprid showed high level of toxicity in seed soaking method, (LC₃₀ = 290, LC₅₀ = 900, LC₉₀ = 14000 ppm) than leaf dip method, (LC₃₀ = 300, LC ₅₀= 1300, LC ₉₀= 56000 ppm). At 18h also, imidacloprid showed high level of toxicity in seed soaking method (LC₃₀= 200, LC₅₀= 500, LC₉₀= 3400 ppm) than leaf dip method (LC₃₀=200, LC₅₀=700, LC ₉₀= 10000 ppm). D. cingulatus is principally a sucking insect and could get the toxicant in higher quantity by feeding on soaked seeds as compared to leaf feeding method. The LT values at 1250 ppm (0.125%) concentration of imidacloprid were found to be 12.4 and 16.6h for seed soaking and leaf dip method respectively. It was observed that at higher concentration of imidacloprid (0.125%), the LT values were lower in seed soaking method and relatively higher in leaf dip method.