Insecticide Susceptibility and Toxicity against Pink Bollworm (Pectinophora gossypiella Saunders) Populations in Cotton
A laboratory study was conducted to evaluate the susceptibility of field populations of the pink bollworm, Pectinophora gossypiella (Saunders), collected from five major cotton-growing tehsils of Bharuch district, Gujarat, during the kharif seasons of 2024-25 and 2025-26. Populations from Amod, Bharuch, Jambusar, Netrang and Valia were tested against seven commonly used insecticides using a diet incorporation bioassay, with a susceptible Surat population as the reference. Larval mortality was assessed across seven concentrations, and LD₅₀-based toxicity indices were used to compare population susceptibility and relative insecticidal toxicity. Mortality increased with increasing insecticide dose across the tested populations. Across insecticides, the highest cumulative mortality in the field populations ranged from 81.25 to 98.65% in Netrang, 82.34 to 93.06% in Bharuch, 67.56 to 90.28% in Amod, 65.45 to 80.38% in Jambusar and 63.70 to 79.73% in Valia. Toxicity-index analysis indicated comparatively greater susceptibility in the Netrang population for most insecticides, whereas Valia and Jambusar generally showed lower susceptibility. Among the tested insecticides, emamectin benzoate, indoxacarb, lambda-cyhalothrin and spinosad showed comparatively higher toxicity, while profenofos and chlorpyrifos were relatively less effective. The observed spatial variation in susceptibility supports the value of location-specific monitoring for insecticide selection and resistance-management planning in cotton. The results provide a laboratory-based comparison of local population susceptibility profiles.