Correlation of catalase and peroxidase to pesticide tolerance in diamondback moth Plutella xylostella (L.)

Catalase (CAT) and peroxidase (POD) were found to exist in the larvae of the diamondback moth Plutella xylostella (L.). Five hours after chlorfluazuron treatment, the activities of CAT in the larvae of three instars all decreased sharply, which were 71.9%, 80.9% and 90.2% of the control respectively. Ten and fifteen hours after treatment, the activity of CAT in the fourth instar larvae rose more than that in the other instar larvae. After treatment with chlorfluazuron to the larvae, the activities of POD in the larvae of three instars were all higher than the control, while the activities of POD in the second and third instar were only 65.0% and 99.2% of those in the control. The result indicated that the CAT and POD activities of diamondback moth showed correlation to the pesticide tolerance. Based on the results of toxicity test, it was clear that the pesticide tolerance of diamondback moth increased with larval instars. The lethal dosage of chlorfluazuron to larvae in the third and fourth instars were 2.65 and 4.07 times respectively, as compared with that in the second instar. The activities of CAT and POD were linear with respect to the quantity of H 2O 2 up to 1.17 and 0.1 mL respectively.