The Relationships among MFO, Glutathione STransferases, and Phoxim Resistance in Helicoverpa armigera

Relationships among MFO, glutathione S-transferases, and phoxim resistance in Helicoverpa armigera (Hübner) were studied. The bioassay results showed that pretreatment of piperonyl butoxide (PBO), O,O-diethyl-O-phenylthiophosphate (SV1), and diethyl maleate (DEM) could increase the toxicity of phoxim in the resistant strain. PBO and SV1 both significantly increased the toxicity of phoxim in R strain; the synergistic ratio (SR) was 3.1- and 6.4-fold, respectively. DEM also had significant synergism on R and S strains; the SR was 6.9- and 2.3-fold, respectively. Relationships among MFO, glutathione Stransferases, and phoxim resistance were determined by biochemistry assay. The results showed that MFO was important for phoxim resistance. The activities of aldrin epoxidase and pNA O-demethylase in the resistant strain were much higher than those in the susceptible strain; the differences were 2.30- and 3.40-fold, respectively, when enzyme activity is expressed in units of mu mol/mg protein/30 min. O-Demethylase might play a more important role than the epoxidase in phoxim-resistant H. armigera. A significant increase in GST activity in the resistant strain was examined and it implied that there is a strong correlation between the enzyme activity and resistance to phoxim.