Abstract: The aims of this study were to reveal the diversity and population differences of symbiotic bacteria of weevils (Curculio spp.) from different host sources, to explore the effects of different host plants on symbiotic bacteria of weevils, and to facilitate further research on the roles of symbiotic bacteria in promoting weevil host adaptation. Two species of weevil were examined, Curculio bimaculatus (multiple hosts), which feeds on Lithocarpus polystachyus, Castanopsis tibetana and Castanopsis sclerophylla, and Curculio davidi (specialized host), which feeds only on Castanopsis tibetana. High-throughput sequencing of the 16S rRNA V3-V4 region sequences of the symbiotic bacteria of weevil larvae was performed using Illumina technology. Community alpha and beta diversity based on OTU (operational taxonomic unit) were calculated. After Illumina quality control, a total of 919980 high quality sequences were obtained, which belonged to 914 OTUs in 24 phyla, 53 classes, 129 orders, 219 families and 400 genera. Proteobacteria, Firmicutes, Actinobacteriota were dominant in all four groups of samples. The alpha diversity of symbiotic bacteria differed between the weevils feeding on different plants, but the community structure was similar as indicated by beta diversity index. Wolbachia and Erwinia were not found in both weevils feeding on Castanopsis tibetana, without significant difference in their alpha diversity. Curtobacterium, Streptomyces and Rhodococcu were lacking in Curculio davidi, and the abundance of Sodalis and Rickettsia was very low. The diversity and abundance of symbiotic bacteria were strongly influenced by plant species that the weevils fed on, while the species of the weevils mainly influenced community structure of symbiotic bacteria. This study may provide a reference for further investigation of the role of symbiotic bacteria in driving the differentiation and adaptation of weevils’ hosts.

Key words: symbiotic bacteria, Curculio spp., 16S rRNA, community structure, host adaptation