Using Airborne eDNA to Assess Hemlock Woolly Adelgid (Adelges tsugae) Infestations and Their Impact on Michigan Coastal Forests

Invasive species colonization degrades ecosystem structure and function, creating a cascade of ecological consequences. Hemlock woolly adelgid (HWA, Adelges tsugae) is an invasive insect that has killed millions of eastern hemlocks (Tsuga canadensis), a foundation species in North America. HWA feed on eastern hemlocks, resulting in tree mortality within several years. In Michigan, land managers depend on early detection to contain infestations and respond through forest-level management. Environmental DNA (eDNA) applications have recently become a powerful biomonitoring tool for invasive species detection. This thesis had two main objectives: we investigated whether molecular analyses could assess HWA infestation level and we used eDNA applications to determine if the presence of HWA is altering plant and arthropod communities. To explore both objectives, we deployed 100 airborne eDNA traps to sample nine infested and six uninfested sites in west Michigan. In Chapter II, we compared relationships among HWA crawler counts, qPCR values, and HWA sistens counts from infested sites. We found that qPCR values and crawler counts are good predictors of HWA infestation levels. We recommend that managers use crawler counts to assess infestation levels because it is an accessible method. In Chapter III, we used amplicon sequencing approaches to assess whether HWA infestations are impacting biodiversity. We compared the plant and arthropod genera detected between infested and uninfested forests and across sites. Plant genera were different across sites, but not between infested and uninfested forests. Arthropod genera differed between infested and uninfested forests and across sites. Results indicated that plant communities are not yet impacted by HWA infestations, but that arthropod communities may be responding to the presence of HWA and hemlock decline. Overall, this thesis provides managers with a tool to optimize management strategies and baseline data to understand how HWA may change communities in the Great Lakes region.