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Harvard Forest Symposium Abstract 2006

  • Title: Population dynamics of the Hemlock Woolly Adelgid
  • Primary Author: Annie Paradis (University of Massachusetts at Amherst)
  • Additional Authors: Joseph Elkinton (University of Massachusetts )
  • Abstract:

    The hemlock woolly adelgid, Adelges tsugae Annand, was originally introduced to the eastern U.S. in the early 1950’s from Osaka, a lowland region of Japan. The insect reached Springfield, Massachusetts in 1991, and currently, inland populations occur as far north as central Massachusetts with some coastal areas infested as far north as Maine. Unlike hemlock stands farther south described by McClure (1987), in which trees die within four to six years, many trees in Massachusetts have been infested for over ten to twelve years. Furthermore, the spread of adelgid across the state has been slower than predicted based on adelgid spread rates occurring further south. In order to document the population dynamics of the adelgid in the northern part of the range where cold temperatures negatively impact survival and fecundity, we constructed a lifetable with data collected between March 2004 and October 2005. This information was then used to determine the conditions under which we expect adelgid populations to stop increasing. We also compared adelgid population rates of increase at several sites in the presence and absence of Sasajiscymnus tsugae (Coleoptera: Coccinellidae) in order to begin assessing the efficacy of this biological control agent.


    Adelgid survival and fecundity both decrease significantly with several aspects of overwintering temperatures, and are positively correlated with tree health. The amount of overwintering mortality required to keep the populations studied from expanding are within the range of values observed in 2003-04. There were no significant differnces in adelgid population rates of increase at sites containing S. tsugae and control sites in 2004 or 2005 (p=0.434; p=0.483). Currently, nothing in our data indicates a difference in adelgid population growth rate between S. tsugae and non-S. tsugae sites.


  • Research Category: Invasive Plants, Pests & Pathogens