Abstract: 　Objective] To explore the relationship between the hemolymph phenol oxidase and melanization of oocysts. [Methods] Anopheles stephensi Plasmodium yoelii system was used to determine the activity of monophenol oxidase (MPO) and o diphenol oxidase (o DPO) in the hemolymph collected from 4 groups of mosquitoes by polyacrylamide gel electrophoresis (PAGE) followed by density scanning. The 4 groups of mosquitoes were: non blood fed (N), normal blood fed (B), infected blood fed (I) and nitroquine administrated (D), respectively. [Results] No significant difference was found in the activities of MPO and o DPO between groups N and B.The activities of MPO and o DPO were not obviously modified in group I, but were significantly increased on day 10 and decreased on day 15 after blood feeding in the group D as compared with those in the groups N and B. [Conclusion]The alteration in the mosquito hemolymph PO activity coincided at each time point with the melanization of Plasmodium yoelii oocysts.

Key words: Plasmodium yoelii, Anopheles stephensi, hemolymph, phenol oxidase, melanization.