Baseline susceptibility of Crotonothrips polyalthiae (Thysanoptera: Phlaeothripidae) to selected insecticides in laboratory

Abstract

Background and objective: Crotonothrips polyalthiae Mound and Nasruddin (Thysanoptera: Phlaeothripidae) is a new but increasingly important pest of asoka tree in Indonesia. Nursery managements rely heavily on insecticides to control the insect, though no information available on the effective insecticides against the pest. Thus, the purpose of the current study was to determine the baseline toxicity and efficacy of 12 insecticides belonging to 8 IRAC’s modes of action on C. polyalthiae in laboratory. Methodology: The C. polyalthiae individuals were collected from active leaf galls of mature ashoka trees that had never been exposed to insecticides. Twelve insecticides belonging to 8 IRAC modes of action (Imidacloprid, abamectin, diafenthiuron, λ-cyholothrin, spinosad, chlorpyrifos, fipronil, deltamethrin, profenofos, permethrin, clofentezin and dicofol) were evaluated for their toxicity against the thrips. Each insecticide was diluted in distilled water with 6 concentrations, including the control. The treatments were arranged in a completely randomized design with five replications. Leaf-dip method was used in the toxicity assay. Results: In general, the insecticides were more toxic against the adults than the larvae of C. polyalthiae. The LC50 values for the adults and the larvae ranged from 19.80-356.97 ppm and from 28.00-415.0 ppm, respectively. Imidacloprid, abamectin, diafenthiuron and λ-cyhalothrin were the most toxic against the adults, while diafenthiuron, imidacloprid, spinosad, abamectin, λ-cyhalothrin, fipronil and chlorpyrifos were the most toxic to the larvae. The results were confirmed by the results of the efficacy test in which only the recommended concentrations were used. Conclusion: Eight out of 12 insecticides tested: Six insecticides recommended for use on thrips of other crops (deltamethrin, abamectin, imidacloprid, fipronil, diafenthiuron and spinosad) and 2 insecticides not recommended for thrips control (λ-cyhalothrin and chlorpyrifos) were effective against the thrips. The study results also presented baseline susceptibility of the insecticides tested and the data could be used as a reference in monitoring future resistance development in the pest.