Integrating Environmental <scp>DNA</scp> Into Early Detection Efforts for an Invasive Terrestrial Beetle

ABSTRACT The economic cost of invasive species continues to rise as more species are introduced globally every year. One of the most effective ways to reduce these costs is to implement robust early detection and rapid response (EDRR) programs, in which invasive populations are detected at low enough abundances that control efforts are effective and cost‐efficient. Environmental DNA (eDNA) surveys have become increasingly common in aquatic invasive species EDRR programs, but they have not been explored for use in terrestrial ecosystem invasions. Here, we investigate the deployment of eDNA surveys to detect invasive coconut rhinoceros beetles ( Oryctes rhinoceros ; CRB) on the island of Oʻahu, Hawaiʻi, USA. CRB impose substantial economic and cultural impacts across Pacific Island nations and territories, with the potential to spread globally. We designed a sensitive, species‐specific molecular assay targeting a 64‐bp segment of the COI region. We tested four field sampling methods at CRB‐positive sites, with roller and mulch‐rinse samples successfully capturing CRB eDNA. We estimated these two methods had per‐sample detection probabilities of 0.47 and 0.54, respectively, in sites with known CRB presence. We then evaluated how these methods performed at low‐ or unknown‐CRB‐abundance sites. The overall per‐sample probability of detection dropped to 0.09 and 0.06 for the roller and mulch methods, respectively, due to low eDNA concentrations in samples. Finally, we compared eDNA detection probability with co‐located pheromone‐baited traps to assess the performance of eDNA against a standard early‐detection protocol. We found that roller eDNA sampling exhibited twice the per‐sample detection probability of traps, with mulch sampling showing comparable patterns, though with greater uncertainty. Our results indicate that eDNA surveys for CRB can be a feasible and useful addition to EDRR programs in Hawaiʻi, and perhaps other sites where CRB are likely to be introduced.