Bioassay for evaluating the resistance level of dusky cotton bug, Oxycarenus hyalinipennis Costa against insecticides sprayed on cotton crop

Dusky cotton bug (DCB), Oxycarenus hyalinipennis, a serious economic sucking insect pest of cotton, is a cosmopolitan polyphagous pest with the potency to develop resistance against insecticides. The resistance was evaluated against insecticides of different chemical nature against DCB population from three cotton fields i.e., unsprayed population (Un-sp), field exposed to sucking sprays (SSp) and field exposed to bollworms sprays (BSp) using semi-opened bolls dip method.The DCB population showed differential range of resistance level against tested insecticides. These RR ratios were among susceptibility (1 fold) and tolerance to low resistance (2-10 fold) for all tested insecticides except for deltamethrin with moderate resistance (11-30 fold) for the populations of both sprayed fields. In the order of resistance for the SSp population, deltamethrin (24.4 fold) was followed by imidacloprid (6.4 fold), profenofos (4.0 fold), cypermethrin (3.2), endosulfan (2.8 fold), chlorfenapyr (2.7 fold) and chlothianidin (2.5 fold). For BSp population, RR ratios from high to low were: deltamethrin (21.2 fold) followed by imidacloprid (4.9 fold), chlothianidin (3.7 fold), cypermethrin (2.8 fold), endosulfan (2.7 fold), triazophos (2.4 fold) and profenofos (2.2 fold). Acephate was highly effective with least LC50 followed by spinosad and dimethoate, whereas, lambdacyhalothrin was least effective. Relative toxicity (RT) order from high to low for SSp population was acephate (1.00) followed by spinosad (1.33), chlorfenapyr (2.69), acetamiprid (2.77) and dimethoate (2.85). For BSp population, RT were sequenced as acephate (1.00) followed by spinosad (1.46), chlorfenapyr (1.67) and dimethoate (3.32). In control unsprayed population, RT were in order as acephate < deltamethrin < spinosad < chlorfenapyr (1.0, 1.20, 1.28 and 1.58, respectively). Lambdacyhalothrin was the least toxic against DCB population of all tested fields. From results, it can be suggested that regular insecticide resistance monitoring is crucial to avoid incidence(s) in O. hyalinipennis, and to adopt the rotational application of appropriate insecticides.