Abstract: Third-instar nymphs of Oedaleus asiaticus were fed on artificial diet mixed with combinations of O. asiaticus  entomopoxvirus (OaEPV) and the insecticides of malathion, chlorpyrifos, β-cypermethrin, cyfluthrin and deltamethrin, in which OaEPV was used as a synergist. Mortalities were observed, and LC₅₀ values and the synergic ratios were determined. The specific activities of two enzymes (carboxylesterase, CarE; glutathione S-transferases, GSTs) in relation to the pest resistance to insecticides were also assayed. The results showed that combinations of OaEPV and chlorp yrifos, β-cypermethrin, cyfluthrin, deltamethrin had no distinct synergism, whereas the combination of OaEPV and malathion was more effective than malathion alone in some degree. The synergic ratio of OaEPV to malathion was 1.42 times. Except del tamethrin, the specific activities of CarE in the midgut of O. asiaticus nymphs treated with mixtures of OaEPV and other insecticides mentioned above were inhibited obviously as compared to insecticide treatments alone. The highest inhibition ratio of CarE specific activity, 4.21 times, appeared when OaEPV was m ixed with malathion. The specific activities of GSTs in the midgut of O. asiaticus treated with the mixtures of OaEPV and cyfluthrin or OaEPV and delta methrin were evidently inhibited as compared to insecticide treatments alone. The specific activities of CarE and GSTs in the fat body of O. asiaticus treated with the mixtures, however, were not significantly changed as compared to insecticide treatments alone. The results suggest that OaEPV enhances the insecticidal effects of chemical insecticides against O. asiaticus by inhibiting the specific activity of CarE in the midgut.

Key words: Oedaleus asiaticus entomopoxvirus (OaEP V), chemical insecticides, synergism, carboxylesterase （CarE）, glutathione S-transferases (GSTs), enzyme activity