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Date of Award

9-2011

Document Type

Campus Access

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Organismic and Evolutionary Biology; Entomology

First Advisor

Joseph S. Elkinton

Second Advisor

Benjamin B. Normark

Third Advisor

Roy G Vandriesche

Subject Categories

Ecology and Evolutionary Biology | Entomology

Abstract

The hemlock woolly adelgid, Adelges tsugae, is an invasive insect from Osaka, Japan threatening populations of eastern hemlock, Tsuga canadensis, and Carolina hemlock, Tsuga caroliniana, in the eastern United States. Previous studies of adelgid population dynamics and hemlock response in the early-1990s suggested that once infested, trees were likely to die within 4 to 6 years; widespread eradication of hemlock throughout the region was expected. However, the vast majority of hemlocks in western Massachusetts are still alive and many are not yet infested, despite the adelgid having been present in the state for 17 years. Many examples of individual trees in Massachusetts harboring adelgid for over ten years have been documented. In order to understand this discrepancy, we conducted detailed lifetable studies of the hemlock woolly adelgid at six locations in Connecticut and Massachusetts from 2004-2008. Adelgid density, fecundity, and survival data as well as temperature and precipitation data were examined to document and understand the apparent stability of adelgid populations in the northeast. These data were also used along with climate projection models to predict the range of suitable habitat for adelgid under two scenarios of carbon emissions through the year 2100.

In an attempt to regulate adelgid populations, several species of biological control agents have been released, including Laricobius nigrinus Fender (Derodontidae), Sasajiscymnus tsugae Sasaji and McClure (Coccinellidae), and Scymnus ningshanensis Yu and Yao (Coccinellidae). Since few studies have addressed the efficacy of these beetles above the branch level, we conducted an experiment to test their effects on adelgid populations using whole-tree enclosures. These data, in addition to adelgid demography data will be useful in predicting future outbreaks, constructing simulations of adelgid growth and spread, and determining the amount of additional mortality needed from a biological control agent to stabilize adelgid populations.

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