Abstract: 【Aim】 This study aims to explore the characteristics of the symbiotic bacterium Tremblaya princeps in Phenacoccus solenopsis through observing its morphology, location and dynamics in different stages of hosts. 【Methods】 The ultrastructure of T. princeps was observed by transmission electron microscopy, and its location and quantitative changes were determined using real-time PCR. 【Results】 T. princeps is located in different tissues compared between females and males of the host P. solenopsis. In females, T. princeps is located only in bacteriome, but not in any other tissues or organs of the host. Size of bacteriome had a significant linear relationship with host body size, and its expanding rate accelerated as the host adults developed. In males of the host, the density of T. princeps increased dramatically before the pupal stage, and then decreased as the adult emerged. Bacteriome collapsed when the males of the host entered the pre-pupal stage. 【Conclusion】 Our results suggest that the infection status of T. princeps is varied with host sexuality and correlated to host individual development.

Key words: Phenacoccus solenopsis, Tremblaya princeps, symbiont, bacteriome, ultrastructure