Aims Spodoptera exigua is a serious pest of many agricultural crops. However, the bacterial communities of S. exigua are poorly studied, particularly over their entire life cycle. We aimed to study the biodiversity of the microbiota across the life cycle of S. exigua and to provide a better and obtain insight into new pest control strategies. Methods and Results The bacterial diversity across the life cycle of S. exigua was studied using Illumina MiSeq sequencing of 16S rRNA genes. Spodoptera exigua is dominated by Proteobacteria and Firmicutes, with a total relative abundance of 90.03%. Enterococcus (24.6%), Pseudomonas (12.2%) and Asaia (45.9%) were abundant and active in eggs, while Methylobacterium (18.7%) and Halomonas (16.5%) dominated freshly eclosed larvae. The 3rd and 5th instar larvae were dominated by Enterococcus (76.3 and 62.0%). Pupal stages had the highest microbial diversity. There was no significant difference between newly emerged males and females. Symbionts of eggs were extremely similar and probably vertically transmitted by males during mating. Conclusions The result showed that the bacterial community was affected by the host developmental stages. Our results also suggest that symbionts of egg mass are probably vertically transmitted control by male spawning adults. Significance and Impact of the Study Our study documents the symbiont bacteria across the life cycle of S. exigua. Understanding the microbial symbionts may provide clues to develop potential biocontrol techniques against this pest.