Host Plant Effects on Activities of Detoxification Enzymes and Insecticide Tolerance in Western Flower Thrips, Frankliniella occidentalis (Insecta)

The polyphagous western flower thrips, Frankliniella occidentalis, is a severe pest of horticultural crops. Individuals from a laboratory population adapted to bean plants were transferred to new host plants, sweet pepper and chrysanthemum, to establish two new populations. The thrips appeared to perform poorly on the new host plants, as the total protein content of individual adults was lowered in the new populations. The specific activities of two insect detoxification enzyme systems, esterases and glutathione S-transferases, were assayed in vitro in the three populations. Host plant shifts had no effect on the level of general esterase activity to α-naphthyl acetate and only a minor effect on the level of glutathione S-transferase activity to 1-chloro-2,4-dinitrobenzene. The new population on pepper plants had slightly lowered glutathione S-transferase activity. The level of tolerance to the insecticide, methiocarb, was not affected by culturing the thrips on new host plants, nor was the total activity per individual of acetylcholinesterase, the target-site enzyme for methiocarb.