Evaluation of insecticide susceptibility variation in different field populations of the cabbage aphid, Brevicoryne brassicae (Hemiptera: Aphididae), to selected organophosphate insecticides.

Abstract

Brevicoryne brassicae (Linnaeus), the cabbage aphid, is a destructive pest of cruciferous crops worldwide. In Kashmir, management relies heavily on organophosphate insecticides, yet regional susceptibility data are lacking. This study evaluated eight field populations for susceptibility to chlorpyrifos, dimethoate, and quinalphos using standardized foliar bioassays with commercial formulations. Probit regression analysis provided reliable dose-response relationships. Resistance ratios (RRs) were calculated relative to the most susceptible field population because a laboratory susceptible strain was unavailable. LC50 values ranged from 3.71 mL L-1 for dimethoate to 4.61 mL L-1 for chlorpyrifos, with resistance ratios between 1.0 and 3.07, all below the threshold for confirmed resistance. Although operational resistance was not detected, some populations showed LC50 values approaching or exceeding recommended field doses, indicating early tolerance. Principal component analysis and hierarchical clustering revealed structured geographic variation in susceptibility, with the Baramulla population forming a distinct cluster. The study provides the first regional baseline of organophosphate susceptibility in Brevicoryne brassicae from Kashmir and highlights the importance of continuous resistance monitoring, insecticide rotation, adoption of integrated pest management strategies, and incorporation of non-chemical control measures to delay resistance development and sustain field efficacy.