Objective To investigate the variation and diversity of symbiotic bacteria both in the second-instar male and female of Ericerus pela .

Method The V3-V4 region of the 16S rRNA was performed using high-throughput sequencing technology. Uparse software was used to cluster the qualified labels. Species annotation was taken by using the Mothur and SILVA's SSUrRNA database to analysis the differences in species abundance and diversity between male and female symbiotic bacteria.

Result There were 1798646 qualified labels identified in this experiment. Cluster analysis was performed with 97% similarity as the standard, and 1 334 OTUs (operational taxonomic unit) were obtained. After the annotation, 14 phylums, 29 classes, 60 orders, 109 families, 165 genera, and 55 species were obtained. E. pela is significantly different from the other insects. For the second-instar nymph, Rickettsia (85.740% in female, 95.462% in male) was the dominant bacteria while Buchnera and Wolbachia were absent. A total of 386 symbiotic bacteria were identified in the second-instar nymphs.

Conclusion The endosymbiotic bacteria of E. pela are quite different from that of other insects. Rickettsia has an absolute advantage in the second-instar nymph of E. pela . Rhizobiales and Bacillales with nitrogen fixation, Sphingomonadales which can synthesize carotenoids, are the subdominant bacteria and occupy a certain proportion in symbiotic bacteria. The unique phenomenon of the E. pela symbiotic bacteria may be related to its unique biological habits, ecological characteristics and nutrition.