Physiological resistance and behavioral avoidance responses to residues of four pesticides by six spider mite populations

Abstract

AbstractSix twospotted spider mite populations were assayed for their levels of physiological resistance and behavioral avoidance to residues of four synthetic pesticides. Mortality could not be estimated for bifenthrin and fenvalerate (synthetic pyrethroids) as mites effectively avoided treated surfaces, however significant between‐population differences in mortality were detected for chlordimeform and cyhexatin. Considerable variation in walkoff and spindown behavioral response to sub‐lethal doses of pesticides was observed among populations within compounds, and within populations among compounds. Within‐compound walkoff and spindown behavioral response varied among all mite populations. Few significant between‐compound correlations were significant, indicating that spider mites responded differently to the four pesticides. The hypothesis that physiological resistance is negatively correlated with behavioral avoidance was tested. Of the four possible negative correlations between physiological resistance and behavioral avoidance for chlordimeform and cyhexatin, only the correlation between cyhexatin‐induced mortality and spindown response was significant. Comparisons of physiological resistance and behavioral avoidance of chlordimeform and cyhexatin by specific pairs of populations did not consistently find these two characters to be related. In a related experiment, the magnitude and direction of the correlation between physiological resistance and behavioral avoidance following selection for increased physiological tolerance to cyhexatin was compared in a highly resistant and a susceptible population of the twospotted spider mite. Mortality in the susceptible population at 2 ppm cyhexatin was similar to mortality in the resistant population at 250 ppm after 72 h exposure (ca. 12%). However, at these concentrations, the resistant population exhibited much higher avoidance of the compound through walkoff response.