INTERFACE BETWEEN CITRUS RUST MITE (ACARI, ERIOPHYIDAE) AND DICOFOL - IMPLICATIONS FOR RESISTANCE MANAGEMENT

Laboratory and field studies were conducted to characterize the interface between citrus rust mite, Phyllocoptruta oleivora (Ashmead), and the acaricide dicofol. Direct and residual (continuous and discontinuous residues) contacts of dicofol on susceptible (S) and dicofol-resistant (R) strains of citrus rust mite were evaluated. The decay in biological activity of different formulations of dicofol was also measured with both strains. Differences between S and R strains were less pronounced in direct contact than residual contact with dicofol. When dicofol was used at high concentrations in residual bioassays (500-1,280 mu g [AI]/ml of water [ppm]), the expression of resistance was very poor on fresh residues of dicofol. However, as residues decayed, we observed substantially greater mortality of the S strain than the R strain. Field studies showed that dicofol on citrus fruits becomes biologically inactive to citrus rust mite relatively fast after its application (concentration of 1,280 ppm [AI]). Both S and R strains survived totally when transferred to a 6-d residue. The formulation of dicofol had an significant effect on the rate of decay in biological activity. Differences in the rate of decay observed in bioassays were consistent with the field performance of dicofol in controlling citrus rust mite.