Abstract
Methods to rear and bioassay the citrus rust mite, Phyllocoptruta oleivora (Ashmead), were developed to detect and characterize resistance to dicofol. Sustained rearing of P. oleivora was achieved on ‘Sunburst’ mandarin seedlings [Citrus reticulate Blanco × (C. paradise Macf. × C. reticulata)] held in Plexiglas cages in the greenhouse. Residual bioassays with dipped or sprayed citrus seedling leaves were used to evaluate the susceptibility to dicofol of P. oleivora populations from groves with known history of its use. Mite populations from groves with no history of dicofol use had significantly higher susceptibility to dicofol than groves in which dicofol was used regularly. Methods using dipped or sprayed leaves gave similar results. With the leaf-dip method, the LCM50 of a susceptible field population (2.81 µmg dicofol/ml distilled water [ppm (AI)]; 95% CL 2.32-3.26) was 8.8 times lower than for a field population selected with dicofol in the laboratory (24.7 ppm [AI]; 95% CL 20.8-28.2). Based on this difference, we established a diagnostic concentration of 10 ppm (AI) for detecting dicofol-resistant mites, with a leaf-dip bioassay. Results of a survey of 19 commercial Florida citrus groves, in which we used diagnostic concentration bioassays to determine susceptibility of P. oleivora to dicofol, revealed significant differences between populations, thus confirming resistance to dicofol.
Published Version
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