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Evaluation of Toxicity of Selected Insecticides against Thrips on Cotton in Laboratory Bioassays
J. D. Lopez Jr., B. K. Fritz, M. A. Latheef, Y. Lan, D. E. Martin, and W. C. Hoffmann
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Adult vial technique (AVT) and spray table bioassays were conducted to evaluate toxicity of selected insecticides against immature and adult thrips, Frankliniella spp. (Thysanoptera: Thripidae). In AVT, technical insecticides comprised of organophosphates (dicrotophos and methamidophos), spinosyn (spinosad) and neonicotinoids (thiamethoxam and imidacloprid) were used. The LC50 values for contact with the insecticides were all significantly different, with spinosad being most toxic and imidacloprid being least toxic to thrips. Spray table tests were conducted with formulated insecticides comprised of dicrotophos, methamidophos and spinosad on thrips-infested greenhouse-grown cotton plants. Multiple treatments of varying droplet sizes and densities were made at 19 L/ha (2 gpa), and thrips were sampled at 1, 3 and 7 days after treatment (DAT). Droplet characteristics (size and density) and DAT did not significantly influence post-treatment thrips densities on cotton plants. Average numbers of thrips/plant on methamidophos- and spinosad-treated cotton plants were significantly fewer than those on dicrotophos-treated and untreated plants. Spray table treatments were also made to examine effects of spray volume [19(2) and 47(5) L/ha(gpa)] and active ingredient (a.i.) rates of spinosad against thrips on cotton at 3, 5, 7 and 14 DAT. Averaged across DAT, increased spray volume rate 47 L/ha provided better control at lower spinosad a.i. rate indicating that improved coverage increased efficacy of spinosad concentrations below label rate.