eDNA for monitoring and conserving terrestrial arthropods: Insights from a systematic map and barcode repositories assessments

Abstract In the past decade, environmental DNA (eDNA) assays have become an essential tool to investigate species presence with samples from the environment instead of collected specimens. eDNA sampling techniques have proved their worth in freshwater and marine studies; now, some trends emerge for their use in terrestrial habitats and particularly to study arthropods. After a systematic review of the literature, we illustrate and analyse the diversity of such studies and discuss their benefits and drawbacks. We identified the most relevant research themes and focused on (i) the taxa and environmental sample types targeted and (ii) the details of the survey scheme. In parallel, we also assessed the available number of sequences from cytochrome c oxidase subunit I (COI), 16S and 18S barcode regions for four major taxa (spiders, centipedes, springtails and insects) in relation to their diversity. We found strong taxonomic and geographic biases regarding coverage per barcode. eDNA research on terrestrial arthropods mainly focuses on insect species that affect humanity in a positive or negative way, and the availability of sequences is much higher for species from temperate‐developed countries than from tropical ones. Moreover, although a high variety of environmental samples are being used, most studies do not assess the barcode completeness of the target taxa nor compare the efficacy of eDNA monitoring technique to other well established and known traditional techniques. Careful workflow designs and comparisons are needed before giving any management or conservation advice as eDNA monitoring does not come without error. Strengths and weaknesses of eDNA assays for conservation are discussed.