Toxicity of cycloxaprid to Aphis craccivora (Koch) and its effects on detoxification enzymes

To investigate the effects of bridged-neonicotinoid compounds on Aphis craccivora (Koch), the toxicity of cycloxaprid and the other three bridged-neonicotinoid compounds on A. craccivora and its effects on detoxification enzymes were determined by leaf dipping method using imidacloprid as the control. The results showed that cycloxaprid and other seven-membered bridged neonicotinoid compounds displayed high insecticidal activities against A. craccivora. The LC50 of cycloxaprid was 3.454 mg/L, which is higher than that of the eight-membered bridged neonicotinoid compounds. The synergistic ratios of enzyme inhibitors DEM and PBO were 4.02 and 3.22, respectively. Both compounds showed remarkable synergistic effects on the toxicity of cycloxaprid, whereas only PBO could significantly enhance the toxicity of imidacloprid. Further enzyme activity tests revealed that the activities of detoxification enzymes, namely, glutathione S-transferase (GSTs) and cytochrome P450 enzymes (7-ethoxycoumarin-O-deethylase) in A. craccivora, could be enhanced significantly (P50 level). Although cycloxaprid could enhance the activities of the above two enzymes to (2.730±0.012) and (0.239±0.009) μmol/(mg pro.·min), respectively, it is still lower than that of imidacloprid. No significant change was observed for the activities of carboxylesterase (CarE). The above results indicated that GSTs and P450s might play key roles during the detoxification of cyclcxaprid in A. craccivora.