## 5 Conclusions  
In conclusion, a preliminary investigation of bacterial communities associated with _O. excavata_ nest was conducted by high-throughput sequencing of the full-length 16S rRNA. These results showed that the bacterial communities in the gut of _O. excavata_ larvae were similar in different samples. This may be caused by similar habitat conditions, which results in a large number of identical bacterial communities in the brood provision and nest soil of different sampling plots. Subsequently, some bacteria entered the larval gut and survived. There was no significant correlation between bacterial communities in the natal environment (brood provision, soil) and the gut of _O. excavata_ larvae. The environment around the nest, including the temperature, light, precipitation, soil moisture, pH and other factors may affect the gut microbiota of bee larvae by affecting the nesting material and nectar source plants. Our findings will contribute to a better understanding of bacterial communities in _O. excavata_ and other wild solitary bees.  
**Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app13031524/s1](https://www.mdpi.com/article/10.3390/app13031524/s1)]([https://www.mdpi.com/article/10.3390/app13031524/s1](https://www.mdpi.com/article/10.3390/app13031524/s1)), Figure S1: The species accumulation curves of sample sizes; Table S1: Bacterial 16 srRNA gene sequencing data; Table S2: Statistics of the number of OTUs at different taxonomic levels; Table S3: Nonparametric multivariate analysis of variance.  
**Author Contributions:** Conceptualization, W.L., Y.L. and D.H.; methodology, W.L., Y.L. and H.L.; software, W.L., Y.L., H.L. and K.Z.; validation, W.L., Y.H., X.D. and Z.Z.; formal analysis, W.L., Y.L., Y.H.; investigation, W.L., Y.L., C.Z., H.L. and H.Z.; resources, Z.Z. and D.H; data curation, W.L., Y.L., H.L. and X.F.; writing--original draft preparation, W.L., Y.L., Y.H. and H.L.; writing--review and editing, W.L., Y.L., D.H., K.Z. and A.L.; visualization, W.L., Y.L. and Y.H.; supervision, D.H.; project administration, D.H. and Z.Z.; funding acquisition, D.H. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by National Natural Science Foundation of China, grant number 31970484; Research on Basic Resources of Science and Technology, grant number 2018 FY100405; The National Natural Science Foundation of China, grant number 32070465; The Key Laboratory of Animal Evolution and Systematics, Chinese Academy of Sciences, grant number E052G21305.  
**Institutional Review Board Statement:** All experiments procedures for this study complied with the current animal ethics guidelines and did not involve any protected animals.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The sequence data that support the findings of this study are openly available in GenBank of NCBI at [[https://www.ncbi.nlm.nih.gov/](https://www.ncbi.nlm.nih.gov/)]([https://www.ncbi.nlm.nih.gov/](https://www.ncbi.nlm.nih.gov/)) (accessed on 18 September 2021). The associated BioProject, SRA, and BioSample numbers are PRJNA763777, SRR15925876, and SAMN21449395, respectively.  
**Acknowledgments:** We are grateful to the editor and reviewers for helpful comments.  
**Conflicts of Interest:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.