Status of the BOLD reference library of DNA barcodes of caddisflies (Insecta: Trichoptera) from the Western Balkans

Background and purpose: Available data in research literature suggest that the Western Balkan countries hold a rich diversity of caddisflies. Assessment and biomonitoring of such rich diversity could be facilitated through DNA-based high-throughput approaches like DNA metabarcoding that depend on the availability of comprehensive reference libraries. Materials and methods: We assessed the status of the COI barcode sequence data for a total of 112 caddisflies species in the investigated region by determining the gaps in representative sequences in the Barcode of Life Data System (BOLD) and examining the accuracy of available records using the Barcode, Audit and Grade System (BAGS). Results: Results revealed a considerable underrepresentation of surveyed geographic region in BOLD records for the target insect group. Moreover, the large majority of the species records were rated “discordant” (72.80% grade E), and only 15.20% were classified as “consolidated concordance or basal concordance” (3.20% grade A and 12.00% B). Approximately 3.20% of the records pertaining to species occurring in multiple BINs (Barcode Index Number) and 8.80% were poorly represented (i.e., less than three specimens, grade D). A fraction of the species graded discordant were deemed concordant after detailed inspection of individual data, decreasing by 14.07%. Conclusions: The assessment of the current state of BOLD entries indicated that DNA barcoding is still not widely applied in Albania, Bosnia and Herzegovina, Montenegro, North Macedonia, Serbia, and Slovenia, emphasizing that Croatia has the most barcoded caddisflies species. The finding that available BOLD Trichopteran records for investigated countries were mainly graded as “discordant” indicates the need for better quality control of reference libraries.