DETECTION AND CHARACTERIZATION OF THE INTERPOPULATION VARIATION OF CITRUS RUST MITE (ACARI, ERIOPHYIDAE) RESISTANCE TO DICOFOL IN FLORIDA CITRUS

Methods to rear and bioassay the citrus rust mite, Phyllocoptruta olei vora (Ashmead), were developed to detect and characterize resistance t o dicofol. Sustained rearing of P. oleivora was achieved on 'Sunburst' mandarin seedlings [Citrus reticulata Blanco x (C. paradisi Macf. x C . reticulata)] held in Plexiglas cages in the greenhouse. Residual bio assays with dipped or sprayed citrus seedling leaves were used to eval uate the susceptibility to dicofol of P. oleivora populations from gro ves with known history of its use. Mite populations from groves with n o history of dicofol use had significantly higher susceptibility to di cofol than groves in which dicofol was used regularly. Methods using d ipped or sprayed leaves gave similar results. With the leaf-dip method , the LC50 of a susceptible field population (2.81 mug dicofol/ml dist illed 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 di agnostic 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 bioas says to determine susceptibility of P. oleivora to dicofol, revealed s ignificant differences between populations, thus confirming resistance to dicofol.