Assessing the use of 3D-printed traps to evaluate Hemlock woolly adelgid (Hemiptera: Adelgidae) infestation levels

Hemlock woolly adelgid, 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, Hemlock woolly adelgid was first detected in 2015 and has spread to several counties in west Michigan. Conservation practitioners are managing Hemlock woolly adelgid 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 Hemlock woolly adelgid responds to treatments. Our main objective was to determine if alternative sampling techniques produce data that is equivalent to field methods, such as randomized branch sampling, for estimating infestation levels. We selected 6 treated sites and 3 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 5 traps at each site to capture adelgid crawlers and performed qPCR analysis to quantify Hemlock woolly adelgid DNA. To determine if trap data could be used as a method to assess Hemlock woolly adelgid infestation levels, we evaluated the relationships between (i) crawler counts and qPCR values (gene copies/reaction), (ii) sistens counts and qPCR values, and (iii) sistens counts and crawler counts. We found that trap data (ie qPCR values and adelgid crawler counts) had comparable correlations with traditional methods, particularly during the peak crawler period. However, the strength of these relationships is influenced by factors such as infestation level and temporal variation.