Comparison of presence of the Elongate Hemlock Scale and Hemlock Wooly Adelgid in Central and Western Massachusetts

The eastern hemlock (Tsuga canadensis) is an important species that is present in northeastern forests because it provides habitat for numerous native species and has an important role in the structure and function of forests. However, its future is being threatened by two invasive insect species: the hemlock wooly adelgid (Adelges tsugae) and the elongate hemlock scale (Fiorinia externa). Both species feed on the sap created by hemlock trees through photosynthesis, leading to needle loss and eventually the tree dies from the insects themselves or being weaker to stressors such as drought or windstorms. In our capstone research project, we examined hemlock trees in towns throughout central and western Massachusetts of varying elevations to determine the impact of average annual temperature on the survival of these invasive insect species. Since both species of insects are killed by extreme cold, we predicted that there would be fewer insects and healthier trees at higher elevations.We observed 30-40 hemlock trees per site along 100m-long transects and recorded insect species abundance into the following categories: not sighted (N.S.), low, mild, and high. Needle coverage on the hemlocks were also categorized as: 0-25%, 25-50%, 50-75%, 75-100%, which was also used as an indication of overall tree health. We found a statistically significant, positive relationship between elevation and low and mild abundance of both species, which means that as elevation increases low or mild abundances increase as well. However, there is not a significant relationship between elevation and high abundance of either insect.