Host plant-induced changes in detoxification enzymes and susceptibility topesticides in the twospotted spider mite (Acari : Tetranychidae)

Adult female twospotted spider mites, Tetranychus urticae Koch, reared on l ima bean plants were moved to cucumber, maize, or new lima beats plants (th e latter being a control) and evaluated after 24 h or 7 d for changes its s usceptibility to three pesticides and in levels of related detoxification e nzymes. The largest and most consistent changes were observed in mites feed ing on cucumber. Susceptibility of mites on cucumber to the synthetic pyret hroids bifenthrin and h-cy halothrin was greater than that of mites reared on lima bean and maize after only 21 h on tile plants, and remained higher after 7 d. Mites on cucumber also were more susceptible to tile organophosp hate dimethoate thats were mites on lima bean, but only after 7 d on the ho st. Susceptilility was inversely related to activities of both general este rase and glutathione S-transferase (GST) in mites on cucumber; general este rase and GST activities were 60 and 25% lower, respectively, than activitie s of twospotted spider mite on lima bean after 7 d of feeding. Mites on mai ze where slightly but significantly more susceptible than those on lima Lea n to bifenthrin, but not to lambda -cy-halothrin. after 7 d and to dimethoa te after 24 h but not after 7 d. General esterase and GST activities in two spotted spider mite fed on maize for 24 h were 20 and 16% higher. respectiv ely, than activities in twospotted spider mite on lima bean, but general es terase activity was 30% lower than lima bean-fed mites and GST was not diff erent after 7 d. Thus, plant-induced changes in general esterase activity. perhaps in combination with GST activity, in twospotted spider mite appear to be inversely related to, and possibly responsible for, changes in suscep tibility of twospotted spider mite to several pesticides. particularly the synthetic pyrethroids. General esterases appear to play less of a role in t he detoxification of the organophosphate insecticide dimethoate.