Modeling Hemlock Woolly Adelgid Spread Throughout the Northeast with Updated Parameter Values

Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Biology Dept.


Chris Moore

Second Advisor

Judy Stone

Third Advisor

Justin Becknell


Hemlock woolly adelgids (Hemiptera: Adelidae, Adelges tsugae Annand; hereafter HWA) have been spreading invasively throughout the Northeastern U.S. since 1951 when they were first introduced from Japan. These pests infest hemlock stands and cause high mortality of eastern hemlock and Carolina hemlock. HWA is found from the Carolinas and Georgia, through the Mid-Atlantic, and northward to Maine and southern Nova Scotia. The ability to predict where HWA will to spread is crucial to informing land managers and conservationists on when and how to protect hemlock stands. To create accurate and precise models, it is helpful to model the past spread of the pest to inform scientists how to model future spread. This study uses a model created by Fitzpatrick et al., 2012 as a base, and updates the parameters values based on more current literature. The original model did not accurately predict HWA arrival in different counties as the observed spread was earlier than the predicted dates. My model alters the fecundity, mortality, and long-distance dispersal values from the original model with a range of values that accounts for updates from recent studies. It also attempts to understand why the base model did not accurately predict the HWA infestation dates. Due to modeling challenges my model cannot be directly compared to the original, however, it sheds light on HWA spread and population dynamics. My model found that altering the winter fecundity did not drastically alter how much area of land was infested, but alterations of winter mortality and long-distance dispersal yielded drastic changes in the area infested. Overall, it is important to recognize that there are possible changes in the fecundity, mortality, and long-distance dispersal of HWA due to climate change. An understanding of alterations to the life cycle and spread of the pest can impact the amount of hemlock stands that become infested.


Hemlock Woolly Adelgid, Landscape Epidemiology, Invasive Pest, Long Distance Dispersal

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