Using surface environmental DNA to assess arthropod biodiversity within a forested ecosystem

Terrestrial arthropods are abundant and diverse with outsized ecological and economic importance. Our ability to monitor this diversity is hampered by the variety of sampling techniques and taxonomic expertise required to catalog the species in an area. DNA metabarcoding approaches show promise but have mainly been limited to trapping studies where DNA is extracted from captured individuals. Here we illustrate the promise of terrestrial plant surfaces as reservoirs of environmental DNA (eDNA) that is rich in arthropod biodiversity information. We posit that collection of surface eDNA will enable easier and more rapid arthropod inventories. We collected 40 paired samples using two novel terrestrial surface eDNA sampling techniques – ‘roller’ tree bark and ‘spray’ foliage sampling – in a New Jersey, USA pine barrens forest. Metabarcoding using two primer sets (COI and 16S) revealed the presence of 177 arthropod families (from 21 orders), representing 80% of the family-level diversity expected in the area based on accumulation curves. Spray samples revealed more families than roller (148 vs. 126), while the two methods showed distinct, though overlapping, community composition. The two primer sets revealed similar alpha diversity, although they also captured different taxonomic subsets. A more limited comparison of roller and spray sampling with traditional aquatic and soil eDNA samples revealed a greater family diversity in surface samples, especially compared with soil. Our study highlights the value of eDNA metabarcoding surveys for achieving the elusive goal of rapid, cost-effective arthropod inventories, and thus realizing a range of ecological research and management goals.