Abstract
Cross-resistance of dicofol-resistant Tetranychus urticae Koch to 21 pesticides was evaluated. Initial investigations used field-collected dicofol-resistant and susceptible colonies. Near-isogenic lines, constructed by a series of backcrosses, were used to confirm or reject determinations of cross-resistance derived from evaluations of field-collected colonies. Dicofol-resistant T. urticae showed strong positive cross-resistance to amitraz, bromopropylate, and chlorobenzilate. Moderate negative cross-resistance to ward chlorpyrifos was observed. These results suggest that amitraz, bromopropylate, and chlorobenzilate should not be used in alternation with dicofol in a resistance management program designed to exploit the instability of dicofol resistance. The uptake and distribution of (14C)-dicofol was investigated in near-isogenic lines of susceptible and resistant mites. No difference in the uptake of radiolabel was observed between strains, suggesting that decreased penetration is not a major mechanism of dicofol resistance. In vivo metabolism studies revealed greater production of water soluble metabolites and lower levels of internal dicofol in the resistant strain compared with the susceptible. Therefore, the major mechanism of resistance to dicofol appears to be increased metabolic detoxification.
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