The quantity of deposited environmental DNA in plant–arthropod interactions depends on taxon, abundance and interaction time

Environmental DNA (eDNA) metabarcoding holds great promise as a simple and efficient tool to detect plant–insect interactions. However, the influence of both abiotic and biotic factors on eDNA deposition in these interactions is not well understood. It especially remains to be tested how much eDNA abundances reflect the frequency or intensity of interactions between insects and plants. We experimentally analysed the quantitative deposition of eDNA from three insect species (the southern green stink bug Nezara viridula, the mustard beetle Phaedon cochleariae and the fall armyworm Spodoptera frugiperda) on leaves of two host plants of varying attractiveness: savoy cabbage (Brassica oleracea var. sabauda, preferred host) and tomato (Solanum lycopersicum, less preferred host). We tested for the effects of insect taxonomy, host plant, exposure time and abundances of interacting insects on the plant material. Our data show a clear quantitative ecological signal in eDNA deposition. Insect abundance and interaction time are reflected in the amount of deposited eDNA. Moreover, significantly more eDNA was deposited on cabbage, the preferred host plant. Besides these ecological drivers, a very strong taxonomic eDNA deposition bias between different insect taxa was observed. eDNA detection is strongly influenced by the ecological interactions of the targeted taxa, highlighting the utility of the tool to specifically detect trophic interactions between plants and arthropods. However, taxonomic biases in eDNA deposition preclude comparative analyses of interactions at the community level.