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.

Environmental DNA (eDNA) analyses have become invaluable for detecting and monitoring aquatic and terrestrial species and assessing site biodiversity within aquatic environments or soil. Recent studies have extended these techniques by using eDNA to identify the presence of aboveground terrestrial arthropods directly from aboveground substrates. However, while the dynamics of eDNA state, transport, and fate (its ‘ecology’) have been explored within aquatic environments and soil, they have yet to be explored within aboveground terrestrial systems. Here we explore the ecology of terrestrial eDNA deposited by fluid-feeding arthropods on leaf surfaces. We carried out a series of experiments to evaluate the optimal filter pore size for intracellular eDNA collection, how eDNA is affected by rain events, and its degradation rate under different solar radiation conditions. We found that the captured concentration of intracellular eDNA was not significantly affected by an increase in filter pore size, suggesting a wide range of viable pore size options exist for targeting intracellular eDNA. We also found extracellular eDNA from fluid excrement degrades more rapidly than intracellular when exposed to solar radiation, indicating the latter is a more viable target for collection. Finally, we identified that rainfall or mist will remove most terrestrial eDNA present on vegetation surfaces. We provide researchers and environmental managers key insights into successfully designing and carrying out terrestrial arthropod eDNA surveys that maximize detection probability.

Environmental DNA (eDNA) analysis has become a valuable tool for detecting aquatic and terrestrial species for monitoring efforts and site biodiversity assessments. However, if aboveground terrestrial eDNA surveys are to be widely adopted, it is necessary to first understand how terrestrial conditions affect the state, transport, and ultimate fate (or ‘ecology’) of terrestrially deposited eDNA. Many of the processes that affect the state, transport, and fate of eDNA in aquatic environments may not be applicable in aboveground systems, warranting an exploration of the terrestrial processes that likely do affect eDNA. Here we explore the ecology of aboveground terrestrial eDNA through a series of experiments evaluating the optimal filter pore size for intracellular eDNA collection, how eDNA is affected by rain events, and its degradation rate under different solar radiation conditions. We found that the captured concentration of intracellular eDNA was not significantly affected by an increase in filter pore size, suggesting there is a wide range of viable pore size options for targeting intracellular eDNA. We also found extracellular eDNA degrades more rapidly than intracellular forms when exposed to solar radiation, indicating the latter is a more viable target for collection. Finally, we identified that rainfall or mist will remove most terrestrial eDNA present on vegetation substrate. This study provides researchers and managers key insights into successfully designing and carrying out terrestrial eDNA surveys that maximize detection probability and minimize false positive results.

Environmental DNA (eDNA) has become a valuable tool for monitoring species of concern or site biodiversity, including expanded use of surveys designed to detect fully terrestrial species. However, if aboveground terrestrial eDNA surveys are to be widely adopted, it is necessary to first understand how terrestrial conditions affect the state, transport, and ultimate fate (or ‘ecology’) of terrestrially deposited eDNA. Many of the processes that affect eDNA’s state, transport, and fate in aquatic environments may not be applicable in aboveground systems, warranting an exploration of the terrestrial processes that likely do affect eDNA. Here we explore ecology terrestrial eDNA through a series of experiments exploring the optimal filter pore size for eDNA collection, how eDNA is affected by rain events, and its degradation rate under different solar radiation conditions. We found that the capture concentration of intracellular eDNA was not significantly affected by an increase in filter pore size, suggesting there is a wide range of viable pore size options for targeting intracellular eDNA. We also found extracellular eDNA degrades more rapidly than intracellular forms when exposed to solar radiation, indicating the latter is a more viable target for collection. Finally, we identified that rainfall or mist will remove most terrestrial eDNA present on vegetation substrate. This study provides researchers and managers key insights into successfully designing and carrying out terrestrial eDNA surveys that maximize detection probability and reduce production of false positive survey results.