Abstract: 【Aim】 The effective coordination between symbiont and host insect innate immunity is an important physiological basis for maintaining their reciprocal relationship. Rickettsia is a dominant symbiont in the whitefly, Bemisia tabaci. The aim of this study is to investigate the regulation of Rickettsia on the expression of the immune genes of B. tabaci adults at different day-old ages. 【Methods】 The expression levels of immune key factor lysozyme gene BtLyz1 and defensin gene Btdef in adult B. tabaci lines with 100% infection, 45.83% infection and no infection by the symbiont Rickettsia were detected and compared, respectively, using qRT-PCR. The expression levels of BtLyz1 and Btdef, apoptosis gene BtCaspase and Rickettsia 16S rRNA gene in 100% Rickettsia-infected adults newly emerged within 24 h and adults at the 3-7-day-old and over 15-day-old were detected, respectively, using qRT-PCR. The correlations between the expression level of 16S rRNA gene of Rickettsia and the expression levels of BtLyz1 and Btdef in B. tabaci adults at different day-old ages were analyzed. 【Results】 The expression levels of BtLyz1 and Btdef in B. tabaci adults infected with the symbiont Rickettsia were significantly increased as compared to those in B. tabaci adults non-infected with Rickettsia. The highest expression level of BtCaspase was observed in B. tabaci adults at over 15-day-old infected with Rickettsia. The expression levels of Rickettsia 16S rRNA gene, BtLyz1 and Btdef  in the 3-7-day-old adults of B. tabaci were significantly higher than those in adults newly emerged within 24 h and at over 15-day-old. The expression level of Rickettsia 16S rRNA gene was significantly positively correlated with the expression levels of BtLyz1 and Btdef in B. tabaci adults newly emerged within 24 h and at the 3-7-day-old, while there was no correlation between the expression level of Rickettsia 16S rRNA gene and the expression levels of BtLyz1 and Btdef in adults at over 15-day-old. 【Conclusion】 The symbiont Rickettsia can upregulate the expression levels of immune-related genes in the host B. tabaci. However, this regulatory effect decreases significantly when the host becomes aging.

Key words: Bemisia tabaci; symbiont, immune gene, lysozyme gene, defensin gene