I have carried out study of insect gut diversity using 16srRNA. We got almost sequences of approximately 50 strains and found out in which seven group of distinct genera formed and gut communities dominated by
16SrRNA is not good for differentiatng between strains, sometimes not even between closely related species. Go for MLSA.
16S is not likely to differentiate between bacterial strains. You should be able to download closely related sequences for the purpose of building phylogenetic trees. Try the SILVA curated database (www.arb-silva.de). If you truly have only 10 or fewer species and can culture them or carry out single cell amplification, sequencing the full genomes will give you the most information.
Agreed. 16S will give you no differentiation at strain level. Full genomes (comparative genomics) will probably give you much more information that you need or want. By the way, your diversity analysis looks remarkably restricted for insect gut bacteria (check out some of the published insect gut metagenome studies). It looks as if you have rather poor coverage.