The impact of competing invasive herbivores on eastern hemlocks

The hemlock woolly adelgid, Adelges tsugae, has been implicated in the decline of hemlock throughout the eastern United States. Eastern hemlock is also attacked by the elongate hemlock scale, Fiorinia externa, which has invaded at least 10 states in the northeast. The interactions between the adelgid and scale, and the role of dispersal and cold tolerance in their range expansion, have never been studied; the results are increasingly important as hemlock stands decline in health and the scale expands its range into that of the adelgid. My work addresses both basic and applied ecological questions in this system and aims at understanding the spread of these invasive species. Some of my research in this area involves assessing the intensity and outcome of adelgid-scale competition occurring when both species colonize the same host plant. The results of these experiments are of considerable practical significance, since understanding how these invasive species interact is essential for predicting their individual and joint effects on hemlock health.