Abstract: [Objective] The combined use of abamectin and triflumuron has synergistic effect on the control of gypsy moths, but the synergy mechanism of abamectin and triflumuron is still unknown. In order to clarify the synergy mechanism of abamectin and triflumuron, 3rd-instar Lymantria dispar larvae were treated with abamectin and triflumuron alone or their combination, and then the activities of detoxification enzymes and protective enzymes were determined, which would provide theoretical basis for the mixture use of the two pesticides. [Method] Abamectin acetone solution of 9 000 μg·mL^-1 or triflumuron acetone solution of 25 000 μg·mL^-1, and the two combination were added to the artificial diet for preparation of poisonous feed for L. dispar larvae. In a low concentration group, the content of drugs was 0.50 μg·g^-1 abamectin or 8.30 μg·g^-1 triflumuron in single pesticide treatment group, and 0.50 μg·g^-1 abamectin plus 8.30 μg·g^-1 triflumuron in mixed pesticide group. In a high concentration group, the content of drugs was 1.10 μg·g^-1 abamectin or 16.60 μg·g^-1 triflumuron in single pesticide treatment group, and 1.10 μg·g^-1 abamectin plus 16.60 μg·g^-1 triflumuron in mixed pesticide group. The third instar L. dispar larvae were fed with the poisonous artificial diet for 24 h. Survivors were counted following activity determinations of detoxification enzyme and protective enzyme. [Result] Mortality analysis showed that all larvae of the control group, single abamectin treatment, and single triflumuron treatment survived from this experiment. The mortality of mixed pesticide treatment group was 1.15% at a low concentration, and 4.11% at a high concentration. There was no significant difference between low concentration group and control, but there was significant difference between the high concentration group and control. Detoxification enzyme activities analysis showed that the activities of CarE and GST of larvae treated with abamectin or triflumuron were significantly higher than those of the control group, while there were no significant differences in the enzymes activities between the mixed pesticide treatment and the control group. Protective enzyme activities assay showed that activities of SOD, CAT and PPO of larvae treated with abamectin, triflumuron, and the two combination were higher than those of control group, however POD activities of treated larvae were lower than that of the control. Meanwhile, activities of SOD, POD and CAT of larvae treated with the mixed pesticides were higher than that treated with either single pesticide, while the case for PPO activity was opposite. [Conclusion] It is concluded that the combined effect of abamectin and triflumuron on Lymantria dispar larvae is mainly through inhibiting the activity of the detoxifying enzymes CarE and GST, and supplemented by inhibiting the activities of protective enzymes PPO, so as to improve the toxicity effect.

Key words: combined mechanism, detoxification enzyme, protective enzyme, pesticide, Lymantria dispar