Foliar Chemistry Linked to Infestation and Susceptibility to Hemlock Woolly Adelgid (Homoptera: Adelgidae)

• Published in: Environmental entomology 2006-02, Vol.35 (1), p.112-120
• Main Authors: Pontius, Jennifer A, Hallett, Richard A, Jenkins, Jennifer C
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Autoecology; Biological and medical sciences; eastern hemlock; exotic pest; forest health; Fundamental and applied biological sciences. Psychology; Plants and fungi; PLANT–INSECT INTERACTIONS; Tsuga canadensis
• ISSN: 0046-225X; 1938-2936
• DOI: 10.1603/0046-225X-35.1.112

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.