Unbound MEDLINE

False ring formation in eastern hemlock branches: impacts of hemlock woolly adelgid and elongate hemlock scale.

Abstract

Herbivores can alter plant physiology through the induction of abnormal wood formation. Feeding by some insects induces the formation of false rings, a band of thick-walled latewood cells within the earlywood portion of the tree ring that reduces water transport. Hemlock woolly adelgid (Adelges tsugae Annand) and elongate hemlock scale (Fiorinia externa Ferris) are invasive insects that both feed on eastern hemlock [Tsuga canadensis (L.) Carrière]. Adelges tsugae has a greater effect on tree health than F. externa, but the mechanism underlying their differential effect is unknown. We explored the effects of these herbivores by assessing growth ring formation in branches of trees that had been experimentally infested for 4 yr with A. tsugae, F. externa, or neither insect. We measured false ring density, ring growth, and earlywood: latewood ratios in the two most recently deposited growth rings. Branches from A. tsugae-infested trees had 30% more false rings than branches from F. externa-infested trees and 50% more than branches from uninfested trees. In contrast, branches from F. externa-infested trees and control trees did not differ in false ring formation. Radial growth and earlywood: latewood ratios did not differ among treatments. Our results show that two invasive herbivores with piercing-sucking mouth parts have differing effects on false ring formation in eastern hemlock. These false rings may be the product of a systemic plant hypersensitive response to feeding by A. tsugae on hemlock stems. If false rings are responsible for or symptomatic of hemlock water stress, this may provide a potential explanation for the relatively large effect of A. tsugae infestations on tree health.

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    • Authors

    Gonda-King L, Radville L, Preisser EL

    Institution

    Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA.

    Source

    Environmental entomology 41:3 2012 Jun pg 523-31

    MeSH

    Animals
    Food Chain
    Hemiptera
    Herbivory
    Introduced Species
    Massachusetts
    Species Specificity
    Trees
    Tsuga

    Pub Type(s)

    Journal Article
    Research Support, U.S. Gov't, Non-P.H.S.

    Language

    eng

    PubMed ID

    22732610