Abstract: 【Aim】 Ultraspiracle protein (USP) belongs to an essential component of a heterodimeric receptor complex with the ecdysone receptor (EcR) which binds ecdysteroids. This study aimed to explore the distribution of USP mRNA in heads of different castes of Polyrhachis vicina Roger adults for inferring the influence of PvUSP on the function or behavior of cranial nerve of P. vicina, and to assess the influence of PvUSP on physiological functions in the body and the relationship with EcR gene by feeding PvUSP dsRNA as RNAi to different castes of P. vicina adults. 【Methods】 We used real-time fluorescent quantitative PCR technique and fluorescence in situ hybridization to test the distribution of PvUSP mRNA expression level in the head of different castes of P. vicina adults, conducted RNAi on different castes of P. vicina adults by feeding PvUSP dsRNA, and used the real-time fluorescent quantitative PCR technique to detect the changes in PvUSP and PvEcR mRNA levels. 【Results】 PvUSP was widely expressed in the head of different castes of P. vicina adults, and especially concentrated in the mushroom body. However, its expression level was quite different in the three castes. The highest expression level was found in the head of workers, the moderate expression level was in the head of male adults, and the lowest was in the head of female adults. After using RNAi technique to silence PvUSP, the expression level of PvUSP mRNA decreased obviously in bodies of different castes of P. vicina adults as compared to the control, and an extremely significant difference was observed (P<0.01), while the expression levels of PvEcR mRNA all increased in different castes. The changes in PvEcR mRNA level in workers and male adults were not distinct （P>0.05), while those in the female body showed a dramatic increase (P<0.05). 【Conclusion】 PvUSP may be related to the structure and functions of nervous system of P. vicina. PvUSP and PvEcR may have relevance in the formation of heterogeneous dimers or function complementarily. PvUSP may influence the reproductive functions of female adults of P. vicina.

Key words: Polyrhachis vicina, ultraspiracle protein (USP), RNAi, ecdysone receptor (EcR), developmental regulation