Volatile Profiles and Resistance to Herbivory in Eastern Hemlock

DEDICATION I fondly dedicate this thesis to the friends and family members who supported me throughout this project and pulled me out of the lab for important life experiences – and especially to Eli Sennesh, for broadening my horizons and enriching my life in countless ways. v ACKNOWLEDGEMENTS I owe tremendous thanks to Joshua Pezet, OEB graduate and Elkinton lab veteran, who pioneered the methods I am using and who trained me in their use. I also gratefully acknowledge the other members of the Elkinton lab for their support, especially Jeff Boettner for his constant advice and encouragement, and Liz Sussky for use of her adelgid population data and for all her efforts in maintaining the Quabbin study site. I am also grateful to my labmates Natashia Manyak, Tessa Dowling, and Courtney Hoffman for their efforts in logistical support. My work on the resistant hemlocks would not have been possible without the prior work of University of Rhode Island investigators, especially Evan Preisser, Richard Casagrande, and their lab members. A special thanks also to Elwood Roberts, who grew the trees I sampled at URI and who climbed a cliff in the rain with me to find good control trees at the New Jersey field site. Many thanks to my advisor and thesis committee members for their insight and generosity with their time: Eastern hemlock hosts the hemlock woolly adelgid, an introduced sap-feeding insect that causes rapid deterioration of the host. Like most conifers, eastern hemlock produces a variety of constitutive and induced defenses, primarily terpenoids. To explore the relationship of terpenoid defenses with adelgid infestations, we artificially infested hemlocks at a forest site and a plantation site, and compared their terpenoid concentrations to those in control trees. Infested trees showed lower terpenoid concentrations than control trees, suggesting that eastern hemlock not only fails to induce production of terpenoids in response to adelgid infestation, but becomes less able to produce carbon-based defenses due to loss of carbon resources to the adelgid. Greater light intensity may account for consistently higher terpenoid concentrations at the plantation site, supporting the explanation that carbon limitation restricts terpenoid production. Recent studies have identified a small number of individual eastern hemlock trees that demonstrate relative resistance to the hemlock woolly adelgid. We compared concentrations of terpenoids in susceptible and relatively resistant trees, both in the forest and in propagated cuttings in a common-garden setting. Terpenoid concentrations were …