Environmental DNA source material
In each experiment, we used an existing assay that targets the internal
transcribed spacer subunit 1 (ITS1) of the brown marmorated stink bug
(Halyomorpha halys ), an invasive pest in many parts of its range
(Valentin et al., 2018). We created a homogenous solution of H.
halys DNA, in multiple states, (i.e. intracellular, intraorganelle, and
extracellular) by collecting paper towels that lined the floor of
enclosures containing H. halys colonies and placing these into 50
ml falcon tubes filled with double deionized water. The tube was shaken,
using a 50 ml vortex adapter, for five minutes to free the excrement
from the paper and suspend it in solution; hereafter called ‘slurry’.
The slurry was removed and evenly distributed among five 5 ml tubes,
which were then stored at –20 C until used for the experiments
described below. We expected freezing would result in some cells within
the slurry to lyse, which would provide us with all three representative
eDNA states (i.e. intracellular, intraorganellar, and extracellular
eDNA) being present for our experiments. The slurry was created to
remove our reliance on H. halys individuals, and its behavior, by
allowing us to ourselves deposit eDNA for experimentation. Furthermore,
given that insect cells, and more generally animal cells, are largely
within the same size range (i.e. 10-20 μm, (Price & Ratcliffe, 1974;
Guertin & Sabatini, 2005) it allowed us to generalize our study for a
wide variety of aboveground species.