Evaluation of sample collection and storage protocols for surface eDNA surveys of an invasive terrestrial insect

Environmental DNA surveys have revolutionized monitoring of rare or cryptic species and species inhabiting areas where conventional sampling is difficult or dangerous. Recent advancements within terrestrial environments include the capture of eDNA deposited by animals on surfaces such as tree bark and foliage, hereafter “surface eDNA.” Notably, a technique which uses commercial paint rollers to aggregate surface eDNA has been deployed with success to detect the presence of forest insect pests providing a potentially powerful new management tool. However, before widespread adoption is feasible, the efficiency and logistics of roller sample collection and study design, especially relative to realistic survey conditions, must be evaluated. We compared the performance of two DNA preservation treatments—cold and ethanol—on their ability to reduce the loss of captured eDNA on rollers over time. Additionally, we evaluated how the detection probability of our target species, the spotted lanternfly (Lycorma delicatula), varied with sampling effort (time spent rolling per sample) and the initial quantity of eDNA present. Finally, we evaluated how the number of trees sampled per roller influenced the final concentrations of lanternfly eDNA remaining on the roller. We found storing rollers with ethanol or cold temperatures resulted in 3–10-fold greater concentrations of experimentally controlled eDNA relative to no treatment after 24 h. Detection probability declined as the amount of lanternfly eDNA decreased, but did not change in response to sampling effort over sample time (10–80 s/tree). Finally, recovered lanternfly eDNA decreased as more trees were sampled by a single roller—a 91% reduction after 7 trees—potentially due to captured DNA being transferred back from the roller onto the bark. Our results provide improved guidance for deploying roller surface eDNA methods for spotted lanternfly surveys, and for invasive insect pest surveillance and monitoring programs generally.