Moving eDNA surveys onto land: Strategies for active eDNA aggregation to detect invasive forest insects

Abstract

The use of environmental DNA (eDNA) surveys to monitor terrestrial species has been relatively limited, with successful implementations still confined to sampling DNA from natural or artificial water bodies and soil. Sampling water for eDNA depends on proximity to or availability of water, whereas eDNA from soil is limited in its spatial scale due to the large quantities necessary for processing and difficulty in doing so. These challenges limit the widespread use of eDNA in several systems, such as surveying forests for invasive insects. We developed two new eDNA aggregation approaches that overcome the challenges of above‐ground terrestrial sampling and eliminate the dependency on creating or utilizing pre‐existing water bodies to conduct eDNA sampling. The first, “spray aggregation,” uses spray action to remove eDNA from surface substrates and was developed for shrubs and other understorey vegetation, while the second, “tree rolling,” uses physical transfer via a roller to remove eDNA from the surface of tree trunks and large branches. We tested these approaches by surveying for spotted lanternfly, Lycorma delicatula, a recent invasive pest of northeastern USA that is considered a significant ecological and economic threat to forests and agriculture. We found that our terrestrial eDNA surveys matched visual surveys, but also detected L. delicatula presence ahead of visual surveys, indicating increased sensitivity of terrestrial eDNA surveys over currently used methodology. The terrestrial eDNA approaches we describe can be adapted for use in surveying a variety of forest insects and represent a novel strategy for surveying terrestrial biodiversity.

Comparison of eDNA and visual surveys for rare and cryptic bromeliad-dwelling frogs

“…Surveys targeting eDNA involve the collection of environmental samples from a location which usually comprises water, soil or sediments (Turner et al, 2015;Buxton et al, 2018;Spitzen-van der Sluijs et al, 2020;Valentin et al, 2020). These samples are then processed following forensic protocols for the extraction of DNA that has been released by organisms into the environment.…”

Environmental DNA is effective in detecting the federally threatened Louisiana Pinesnake (Pituophis ruthveni)

“…Both species‐specific and metabarcoding studies have highlighted the importance of sampling strategy for eDNA detection in aquatic and terrestrial systems (Gasparini et al., 2020; Goldberg et al., 2018; Harper, Handley, et al, 2019; Lawson Handley et al., 2019; Leempoel et al., 2020; Valentin et al., 2020). Concerning crayfish burrow commensals, such as the Eastern Massasauga and Kirtland's Snake, crayfish burrows are often complex (Hasiotis & Mitchell, 1993), and snake movements within them are poorly understood.…”

“…These elements individually or combined may explain the low eDNA detection rates observed for semi‐fossorial and/or semi‐aquatic snakes in previous investigations (Baker et al., 2018; Halstead et al., 2017; Merkling, 2018; Ratsch et al., 2020; Rose et al., 2019). As such, snake eDNA detection may be improved through sampling strategies that consider species’ ecology and behavior, enable greater and continuous soil coverage at higher replication (Leempoel et al., 2020; Zinger et al., 2020) or aggregate eDNA on various terrestrial substrata (Valentin et al., 2020), and account for abiotic and biotic factors.…”

“…Over the past decade, the utility of eDNA analysis has grown rapidly, and its efficacy has been demonstrated from freshwater, marine, subterranean, terrestrial, and airborne samples (e.g., Franklin et al., 2019; Harper et al., 2020; Johnson, Cox, & Barnes, 2019; Niemiller et al., 2018; Thomsen et al., 2012). Since eDNA analysis was first applied to macrobiota (Ficetola et al., 2008), it has become an important conservation and management tool that is capable of detecting both invasive and imperiled species at low abundances in numerous contexts (e.g., Gasparini, Crookes, Prosser, & Hanner, 2020; Goldberg, Strickler, & Fremier, 2018; Kessler, Ash, Barratt, Larson, & Davis, 2020; de Souza, Godwin, Renshaw, & Larson, 2016; Tréguier et al., 2014; Valentin et al., 2020; Wacker et al., 2019).…”

Soil stabilisation for DNA metabarcoding of plants and fungi. Implications for sampling at remote locations or via third-parties

“…As the use of eDNA metabarcoding has extended to the study of soils in more remote locations (Tedersoo et al 2014;Detheridge et al 2020) and to more applied deployment in nature conservation site monitoring by statutory organisations (Geml et al 2014;Detheridge et al 2018;Latch 2020;Valentin et al 2020), the issue of soil storage between sampling and subsequent analysis has become an important consideration. Such concerns have interested soil scientists for many decades, but usually in relation to the metabolic status of soil organisms, assessed via community level physiological profiles (CLPP), soil respiration etc.…”