Journal of Chemical Ecology (2014) 40, 1003-1012

E. Alexa McKenzie, Joseph S. Elkinton, Richard A. Casagrande, Evan l. Preisser and Mark Mayer (2014)
Terpene chemistry of eastern hemlocks resistant to hemlock woolly adelgid
Journal of Chemical Ecology 40 (9), 1003-1012
Abstract: Recent studies have identified a small number of individual eastern hemlock trees that demonstrate relative resistance to the introduced sap-feeding insect, the hemlock woolly adelgid. Using gas chromatography, we compared concentrations of twenty-two terpenoids in susceptible and relatively resistant trees, both in the forest and in propagated cuttings in a common-garden setting. Terpenoid concentrations were higher in twig tissue of resistant versus susceptible trees, across six sampling dates and at both sites. These changes may be particularly important because the hemlock woolly adelgid feeds on twig tissue. Because the common-garden cuttings were free of herbivores, the higher terpenoid concentrations are interpreted as a constitutive defense. Increased levels of monoterpenes and sesquiterpenes imply an overall increase in the input of carbon precursors to both terpenoid synthesis pathways.
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Link to article at publishers website

Research topic(s) for pests/diseases/weeds:
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Adelges tsugae	Hemlock (Tsuga)