Building a reliable 16S mini-barcode library of wild bees from Occitania, south-west of France

DNA barcoding and metabarcoding are now powerful tools for studying biodiversity and especially the accurate identification of large sample collections belonging to diverse taxonomic groups. Their success depends largely on the taxonomic resolution of the DNA sequences used as barcodes and on the reliability of the reference databases. For wild bees, the barcode sequences coverage is consistently growing in volume, but some incorrect species annotations need to be cared for. The COI (Cytochrome Oxydase subunit 1) gene, the most used in barcoding/metabarcoding of arthropods, suffers from primer bias and difficulties for covering all wild bee species using the classical Folmer primers.

We present here a curated database for a 250 bp mini-barcode region of the 16S rRNA gene, suitable for low-cost metabarcoding wild bees in applications, such as eDNA analysis or for sequencing ancient or degraded DNA. Sequenced specimens were captured in Occitania (south-west of France) and morphologically identified by entomologists, with a total of 530 individuals belonging to 171 species and 19 genera. A customised workflow including distance-tree inferences and a second round of entomologist observations, when necessary, was used for the validation of 348 mini-barcodes covering 148 species. Amongst them, 93 species did not have any 16S reference barcode available before our contribution. This high-quality reference library data are freely available to the scientific community, with the aim of facilitating future large-scale characterisation of wild bee communities in a context of pollinators' decline.