Effects of abamectin on the three detoxification enzyme systems in Bactrocera cucurbitae(Coquillett)

【Objective】 The purpose of the study was to explore the effects of abamectin on the detoxification enzyme system of Bactrocera cucurbitae(Coquillett), to clarify the relationship between abamectin resistance and detoxification enzymesin B. cucurbitae,and to provide theoretical basis for the comprehensive management of B. cucurbitae resistance and the scientific use of medication.【Method】 The feeding toxicity method was used to determine the sublethal concentration(LC₂₅) and lethal concentration(LC₅₀) of abamectin on susceptible strain(SS) and abamectin resistant strain(RS) of adult B. cucurbitae. Microplate method was used to determine the activities of glutathione S-transferase(GSTs) and carboxylesterase(CarE) in adults of SS and RS strains and those treated with LC₂₅ and LC₅₀ doses for 12,24,48 and 72 h. Cytochrome P450 monooxygenases(P450s) content was determined by ELISA kit method. The changes in GSTs, Michaelis constant(K_m) and maximal velocity(V_max) values and synergistic effects of synergists diethyl maleate(DEM),triphenyl phosphate(TPP) and potentiometric booster ether(PBO) on abamectin were tested and analyzed in the adults of SS and RS strains.【Result】 The activities of GSTs and CarE in the RS strain were significantly increased(P<0.05,the same below) compared with those in the SS strain,which were 2.92 and 1.46 times of that in the SS strain,while the P450 content was significantly decreased,which was 68.0% of that in the SS strain.After being exposed to LC₂₅ for 12,48 h and LC 50 for 12,24,48 h in SS strain and LC₂₅ for 12 h,LC₅₀ for 72 h in RS strain of abamectin,theactivities of GSTs were induced to be significantly enhanced. CarE activity was induced to be significantly enhanced at 24 h after LC₂₅ dose treatment in the SS strain and was significantly inhibited at 72 h after LC₂₅ treatment and at all times after LC₅₀ treatment in the RS strain. The content of P450s was decreased at 12 h after LC 50 treatment and was increased at 72 h after LC₅₀ treatment. Compared with SS strain,the K_m value of GSTs in the RS strain was significantly reduced and V_max was significant increased,and the K_m and V_max of CarE were not significantly changed. The synergistic ratios of synergists DEM,TPP and PBO were 1.03,1.04 and 2.08 in the SS strain and 3.45,2.52 and 2.26 in the RS strain,with relative synergistic coefficients of 0.71,0.60 and 0.54 respectively.【Conclusion】 The GSTs and CarE detoxification enzymes are involved in the formation of resistance to abamectin in B. cucurbitae.Among them,GSTs activity has quantitative and qualitative changes, and their increased affinity for substrates and faster metabolism play a leading role in B. cucurbitae to form abamectin metabolic resistance.