Host plant effects on activities of detoxification enzymes and insecticidetolerance in western flower thrips, Frankliniella occidentalis (Insecta)

The polyphagous western flower thrips, Frankliniella occidentalis, is a sev ere pest of horticultural crops. Individuals from a laboratory population a dapted to bean plants were transferred to new host plants, sweet pepper and chrysanthemum, to establish two new populations. The thrips appeared to pe rform poorly on the new host plants, as the total protein content of indivi dual adults was lowered in the new populations. The specific activities of two insect detoxification enzyme systems, esterases and glutathione S-trans ferases, were assayed in vitro in the three populations. Host plant shifts had no effect on the level of general esterase activity to alpha-naphthyl a cetate and only a minor effect on the level of glutathione S-transferase ac tivity to 1-chloro-2,4-dinitrobenzene. The new population on pepper plants had slightly lowered glutathione S-transferase activity. The level of toler ance to the insecticide, methiocarb, was not affected by culturing the thri ps on new host plants, nor was the total activity per individual of acetylc holinesterase, the target-site enzyme for methiocarb.