Abstract: 【Aim】 This study aims to uncover the antioxidant defense mechanisms in Spodoptera liturae larvae infected by the fungus Nomuraea rileyi.【Methods】 We measured the changes in the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in the infected larvae of S. litura at different instars and compared the influences of different inoculation approaches including spraying method and dipping method on antioxidase activities in the infected larvae. 【Results】 The POD activity was not detected in both the infected larvae and the non-inoculated larvae (the control) of S. litura. The activities of SOD and CAT in the infected larvae were significantly higher than those in the control at the early stages of infection. However, the activities of SOD and CAT in the infected 2nd and 3rd instar larvae dropped sharply after reaching the peak at 16 h after inoculation. The antioxidase activities in the infected 4th and 5th instar larvae kept a high level for a long time and then turned lower than those of the control at 60-72 h after infection. The activities of SOD and CAT in the infected larvae which were inoculated with dipping and spraying methods were significantly higher than those of the control, and the dipping method had a greater effect on antioxidase activities than the spraying method in the 2nd and 3rd instar larvae, but there was no significant difference in the effects on the antioxidase activities in the 4th and 5th instar larvae between the two methods. 【Conclusion】 The antioxidase activities in S. litura larvae are greatly affected by the infection of N. rileyi. The activities of SOD and CAT increase first, and then decrease, and the trend of the change is closely related to the developmental stage of the larvae. The dipping method has a stronger influence on the SOD and CAT activities in the 2nd and 3rd instar larvae than on those in the 4th and 5th instar larvae when the body integument inoculation quantities are at the similar level.

Key words: Spodoptera litura, Nomuraea rileyi, antioxidant defense, antioxidant enzymes, superoxide dismutase, catalase, enzyme activity