Author: Spencer  Christian  DeBrock

Major: Zoology

Graduation Year: 2018

Thesis Advisor: Allison Gardner

Description of Publication: The black-legged tick (Ixodes scapularis) has recently made a tremendous impact in Maine due to its role as a vector for the bacterial pathogen Borrelia burgdorferi, the causative agent of Lyme disease. A lesser known, but equally concerning, invasive insect is the hemlock woolly adelgid (HWA; Adelges tsugae), a sap-sucking scale that is primarily responsible for the ongoing widespread decline of eastern hemlock in the northeast. Maine is currently experiencing a co-invasion of these species, and this study tests the hypothesis that the phenomenon of hemlock loss may facilitate the invasion of the black-legged tick by a combination of indirect effects. By killing eastern hemlock trees, the HWA alters forest structure (e.g., letting more light through the canopy) and changes the species composition of plant and wildlife communities, including important hosts of the black-legged tick. My study simulates the consequences of HWA infestation by comparing tick abundance and nymphal infection prevalence (NIP) in hemlock and hardwood stands in southern Maine and the Bangor area. I hypothesized that the HWA is indirectly increasing both tick abundance and Lyme disease risk in Maine by creating ecological conditions that alter abundance of deer and provide a more suitable microhabitat for the tick. I also predicted that NIP would differ between the two treatments, with ticks collected in deciduous stands having higher infection prevalence. My results showed no significant difference in either tick abundance or NIP between the two treatments. Additionally, I tested one mechanism that could explain these patterns by conducting deer scat surveys using standardized transects. There was no significant difference in deer scat counts between the treatments. Conclusions from this work could inform park managers and Maine citizens about the likelihood of Lyme infection or tick bites in certain areas of forests or parks.

Location of Publication:

URL to Thesis: https://digitalcommons.library.umaine.edu/honors/322