Detection of a cryptic terrestrial insect using novel eDNA collection techniques

Abstract

Sensitive detection techniques are key to inform management practices for invasive and pest species by identifying the pest species’ distribution or identifying the presence of biological control agents that may negate the need for chemical control. Environmental DNA (eDNA) can be detected to infer the presence of rare, cryptic, and invasive species. This study provides a method that expands the application of eDNA techniques within terrestrial systems. Our study is focused on a cryptic biological control agent of the pointed snail Cochlicella acuta, the fly parasitoid Sarcophaga villeneuveana, which remains within the snail shell for most of its lifecycle, making it difficult to detect. Three sites were sampled using traditional surveys and three types of eDNA sampling 1/ crushing live snails, 2/ water washing live snails, old snail shells or vegetation, and 3/ vacuuming live snails or vegetation. An assay was developed to amplify a 129 bp fragment of S. villeneuveana, with positive detections recorded in crushed snail samples, water washed live snail, water washed vegetation, and laboratory vacuumed vegetation. Presence of the endoparasitoid was validated by traditional survey techniques conducted at the same time, indicating that all techniques tested are comparable for detection of the parasitoid. The new technique which only requires a small vegetation sample from the field post-harvest and a portable vacuum has great potential to be applied to other insects and environments, particularly cryptic species, pests, and biological control agents in crops.