Abstract: The activities of protective enzymes peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) in prediapause, diapause, and postdiapause larvae of Sitodiplosis mosellana Gehin were determined by using protective enzyme testing kits. The results indicated that the activities of the three protective enzymes showed a decreasing trend from prediapause to early diapause larvae. In one-year cycle, the SOD and CAT activities of diapause larvae had the same responses to environmental temperature, i.e., increased at lower temperature but decreased at higher temperature, while POD activity was related to both environmental temperature and the development situation of the larvae. A similar seasonal variation trend was observed in the three protective enzymes of both no-cocooned and cocooned larvae in one-year cycle. The three protective enzyme activities of no-cocooned larvae were higher than those of cocooned larvae at the same diapause stage. No significant difference of the three protective enzyme activities was found between 1st and 2nd year diapause larvae. The activities of the three protective enzymes increased gradually with the development of post-diapause larvae.

Key words: Qinzhou Bay, phytoplankton, species composition, community diversity.