Insecticide resistance status of Hyposidra talaca (Lepidoptera: Geometridae) in major tea growing zone of India

Management of the black looper Hyposidra talaca (Walker), the most demolishing foliage feeder of tea in Himalayan foothills, is based on the use of chemical insecticides, though poor field efficacy of various commercially formulated products has recently been reported. In the present study, insecticide resistance of H. talaca to some traditional and newer insecticides was evaluated from north-eastern tea growing belt of India. Six populations of H. talaca were collected in three consecutive years, 2017 to 2019, from five locations (Dooars, Kalimpong, Sikkim, Assam, and Darjeeling). These areas represent the major and commercially exportable best-quality Indian tea production belts. The Darjeeling and Assam populations showed low to very high lethal concentration ratios (LCRs) (16.67 to 140.32, respectively) to bifenthrin, deltamethrin and diflubenzuron while, highest LCR to quinalphos was observed in the Dooars population (119.81). Similarly, very low to extremely high LCRs to emamectin benzoate and flubendiamide (4.00 to 65.25 and 16.43 to 148.94, respectively) were observed in all six populations. However, pyridalyl (LCR ≤ 77.09) and spinetoram (LCR ≤ 82.03) showed higher toxicity than that of cyantraniliprole (LCR ≤ 120.98) to field populations of H. talaca, irrespective of locations. The pairwise correlation coefficients of log LC50 values revealed that emamectin benzoate was significant but negatively correlated with bifenthrin. LCRs to the tested insecticides were heterogeneous and highly variable among locations and years. Specific resistance management strategies should be established, especially in locations where H. talaca has developed very high levels of resistance to newer chemistry insecticides.