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1 February 2006 Foliar Chemistry Linked to Infestation and Susceptibility to Hemlock Woolly Adelgid (Homoptera: Adelgidae)
Jennifer A. Pontius, Richard A. Hallett, Jennifer C. Jenkins
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Hemlock woolly adelgid (Adelges tsugae Annand) is an invasive insect pest that is causing widespread mortality of eastern hemlock. However, some stands remain living more than a decade after infestation. To date, this has been attributed to site and climatic variables. This multi-tiered study examines the role foliar chemistry may play in A. tsugae success and subsequent hemlock decline. Comparisons of resistant and susceptible hemlock species indicate higher concentrations of P and lower concentrations of N in resistant species. On experimentally colonized hemlocks, the numbers of live sistens present after two A. tsugae generations was correlated with higher K and lower P concentrations. A regional T. canadensis monitoring effort showed that concentrations of Ca, K, N, and P were most strongly correlated with A. tsugae densities, which was the driving factor in hemlock decline. From the results of this study, we hypothesize that higher N and K concentrations may enhance hemlock palatability, thereby increasing A. tsugae population levels, whereas higher concentrations of Ca and P may deter more severe infestations. Foliar chemistry alone can explain over one-half of the variability in hemlock decline witnessed at 45 monitoring plots across the northeastern United States. Combining chemistry and traditional site factors, an 11-class decline rating could be predicted with 98% 1-class tolerance accuracy on an independent validation set. These results suggest that foliar chemistry may play a role in eastern hemlock susceptibility to A. tsugae infestation and should be included in risk assessment models.

Jennifer A. Pontius, Richard A. Hallett, and Jennifer C. Jenkins "Foliar Chemistry Linked to Infestation and Susceptibility to Hemlock Woolly Adelgid (Homoptera: Adelgidae)," Environmental Entomology 35(1), 112-120, (1 February 2006).
Received: 2 April 2005; Accepted: 1 July 2005; Published: 1 February 2006

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eastern hemlock
exotic pest
forest health
Tsuga canadensis
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