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    Author(s): Michael E. Montgomery; Anthony F. Lagalante
    Date: 2008
    Source: In: Onken, Brad; Reardon, Richard, comps. Fourth Symposium on hemlock woolly adelgid in the eastern United States; 2008 February 12-14; Hartford, CT. FHTET 2008-01. Morgantown, WV: U.S. Forest Service, Forest Health Technology Enterprise Team: 118-123.
    Publication Series: Other
    Station: Northern Research Station
    PDF: View PDF  (405.81 KB)

    Description

    The terpenoid profiles in the needles of the hemlock species were found to be related to geographic distribution of the species and their presumed ancestry. Although a definitive association of individual terpenoids with resistance to the hemlock woolly adelgid (HWA), Adelges tsugae Annand, was not identified, isobornyl acetate and α-humulene seem to be linked with resistance. Variability in space and time of several components may be as important in determining resistance as the level of a specific terpenoid. Seasonal variability is higher in the leaf cushion, where HWA feeds, than in the needle where the terpenoids are stored. High levels of isobornyl acetate (or its isomer bornyl acetate) are also a characteristic of the foliage of many other North American conifers. We hypothesize that selective pressure from native defoliators such as the hemlock looper, in the absence of native adelgids and scale insects, may have resulted in the phytochemistry of the Tsuga species in eastern North America drifting away from protection against sucking insects. Studies of the nutrients and semiochemicals in the leaf cushion xylem ray parenchyma, where the adelgid feeds, are needed to further define the basis of hemlock resistance to HWA.

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    Citation

    Montgomery, Michael E.; Lagalante, Anthony F. 2008. The role of volatile terpenoids in the relationship of the hemlock woolly adelgid and its host-plants. In: Onken, Brad; Reardon, Richard, comps. Fourth Symposium on hemlock woolly adelgid in the eastern United States; 2008 February 12-14; Hartford, CT. FHTET 2008-01. Morgantown, WV: U.S. Forest Service, Forest Health Technology Enterprise Team: 118-123.

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