Abstract: Objective To clone, locate and differentially analyze the transcription factor Relish gene from Anopheles stephensi, and to examine its signals-modulating action on prophenoloxidase cascade and melanization of Plasmodium yoelii oocysts. Methods Relish cDNA of total mosquitoes was amplified by RT-PCR with degenerated primers. Target PCR product was purified，cloned，sequenced and identified. Special Relish gene was amplified with specific primers from hemocytes or midgut，respectively. Semi-quantitative analysis was made under different feeding conditions. Relish message ribonucleic acid was identified with hybridization in situ. Results One cDNA segment of Relish similar to An.gambiae was acquired from An. stephensi. The same Relish gene was also manifested in the hemocytes and midgut. Marked up-regulation expression of Relish was observed at 6，12，24 or 48 h of Plasmodium yoelii infection and at 12 and 24 h after sucking nitroquine-acetate sucrose solution，that was before inducible oocyst melanization. Relish was also expressed in the hemocytes and midguts by ISH. Conclusion Transcription factor Relish of An. stephensi might play a role in signal modulation of Plasmodium yoelii infection and oocyst melanization.

Key words: Anopheles stephensi, Transcription factor, Signal modulation