The defending enzymes in abamectin resistant Plutella xylostella

Key Words：Plutella xylostella, abamectin, resistance, defending enzymes

Abstract：         The endogenous enzymes of the immune systems of abamectin susceptible (ABM-S) and resistant (ABM-R) Plutella xylostella (L.), including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), were examined to determine whether their activities were affected by insecticide resistance. These three enzymes′ activities were positively correlated with larval stage in terms of enzyme activity per larva. On the whole, SOD, POD and CAT activity was lower in the ABM-R strain than in the ABM-S strain. Differences in SOD activity between the two strains decreased with each developmental stage. In the first to second instars, SOD activity in the ABM-S strain was 14.27fold higher than in the ABM-R strain. The biggest difference in POD activity was observed in the third instar, in which there was 4.28fold difference between strains. There was no significant difference in CAT activity between the late fourth instars of each strain but 1 to 2 fold difference in the activity of this enzyme was found in other developmental stages. These results indicate that pesticide resistance does not induce an increase in antioxidant enzyme activity, which suggests that there is a kind of energy conservation in the insect enzyme system.