Assessing the use of 3D printed traps to evaluate Hemlock Woolly Adelgid (Hemiptera: Adelgidae) infestation levels

Hemlock woolly adelgid (HWA), Adelges tsugae (Annaand), is an invasive
insect that has devastated millions of eastern hemlocks, Tsuga canadensis
(L.) Carrière, in eastern North America since the 1950s. In Michigan, HWA
was first detected in 2015 and has spread to several counties in west
Michigan. Conservation practitioners are managing HWA through a statewide,
landscape-level pesticide management plan. The traditional method of using
randomized branch sampling to estimate infestation levels is
time-consuming but allows managers to monitor how HWA responds to
treatments. Our main objective was to determine if molecular techniques
could replace traditional methods for estimating infestation levels. We
selected six treated sites and three untreated sites in west Michigan.
During the fall and winter of 2022, we estimated the densities of the
sistens generation using a randomized branch sampling method, and during
the summer of 2023, we deployed five traps at each site to capture adelgid
crawlers and performed qPCR analysis to quantify HWA DNA. To determine if
qPCR is an appropriate method to assess HWA infestation level, we used
linear regressions to determine whether relationships existed between (1)
crawler counts and qPCR values, (2) sistens counts and qPCR values, and
(3) sistens counts and crawler counts. We found that qPCR analyses and
adelgid crawler counts have comparable, strong correlations with
traditional estimation methods, particularly during the peak crawler
period. Managers can use either qPCR or crawler counts from the peak
crawler period to understand how HWA infestations respond to treatment or
to prioritize treatment in high-risk areas.