The UT Knoxville Libraries, where I am employed as a librarian (https://libguides.utk.edu/veterinaryinformation) subscribe to the Web of Science Core Collection database. We also provide access to other databases relevant to this review on the Web of Science platform, including CAB ABSTRACTS, Biological Abstracts, BIOSIS citation index, Zoological Record, and SciELO Citation Index. These plus all several others are searched if "All Databases" is selected via the drop-down menu via the "Select a database" function at the top of the screen.
Which additional databases are available on the Web of Science platform by choosing "All Databases" varies from institution to institution. Example: I searched on 1/7/2018 after choosing "All Databases" the same keywords yielded 405 citations:
405 TOPIC: (wolbachia AND coleoptera) OR TOPIC: (wolbachia AND beetles)
So I suggest that more specific information be supplied about which databases were searched, perhaps in the supplemental information section of the preprint.
For more information about how to do this according to PRISMA checklist, please see items #7 (Information Sources--it asks that authors supply "databases and dates of coverage") and #8 (Search--"Present full electronic search strategy for at least one database, including any limits used, such that it could be repeated") on the PRISMA checklist.
Please also consider searching Google Scholar. Please see Bramer et al " Optimal database combinations for literature searches in systematic reviews: a prospective exploratory study." https://www.ncbi.nlm.nih.gov/pubmed/29208034