research

Identification, evaluation,
and propagation of adelgid-resistant eastern hemlocks

Although a number of studies have documented the resistance of several hemlock species (Tsuga spp.) to hemlock woolly adelgid (HWA; McClure 1992, Pontius et al. 2002, Lagalante and Montgomery 2003), there is currently no evidence for HWA resistance in either eastern or Carolina hemlocks (Tsuga canadensis and T. caroliniana). Two decades of HWA-linked hemlock death along the East Coast demonstrates that HWA resistance, if it exists, is exceedingly rare among T. carolina and T. canadensis. Despite the adelgid’s devastating effects, however, there is anecdotal evidence for the persistence of a few apparently healthy hemlocks in HWA-infested areas. Evaluation of these surviving hemlocks for HWA resistance in situ is complicated by the fact that adelgid susceptibility is a function of plant health, winter temperatures, and growing conditions in addition to innate plant resistance (McClure and Cheah 2002, Pontius et al. 2006). We are currently surveying HWA-devastated stands of eastern hemlocks for surviving mature trees; our research takes advantage of decades of HWA-mediated natural selection of hemlocks to identify potentially resistant and/or tolerant individuals. When potentially resistant and/or tolerant trees are identified, we will take and propagate cuttings from them in order to evaluate these plants for HWA resistance/tolerance under standardized conditions.

For a great description of the effects of hemlock woolly adelgid, take a look at "A Death in the Forest," written by Richard Preston for The New Yorker.
Click here to download PDF.

  • Lagalante, A., and M. Montgomery. 2003. Analysis of terpenoids from hemlock (Tsuga) species by solid-phase microextraction/gas chromatography/ion-trap mass spectrometry. Journal of Agricultural & Food Chemistry 51:2115-2120.
  • McClure, M. 1992. Hemlock woolly adelgid. American Nurseryman 3/15/1992:82-89.
  • McClure, M., and C. Cheah. 2002. Important mortality factors in the life cycle of hemlock woolly adelgid Adelges tsugae in the northeastern United States. Pages 13-22 in R. Reardon, B. Onken, and J. Lashomb, editors. Symposium on the hemlock woolly adelgid in eastern North America. New Jersey Agricultural Experiment Station, New Brunswick, NJ.
  • Pontius, J., R. Hallett, and M. Martin. 2002. Examining the role of foliar chemistry in hemlock woolly adelgid infestation and hemlock decline. Pages 86-99 in R. Reardon, B. Onken, and J. Lashomb, editors. Symposium on the hemlock woolly adelgid in eastern North America. New Jersey Agricultural Experiment Station, New Brunswick, NJ.
  • Pontius, J., R. Hallett, and J. Jenkins. 2006. Foliar chemistry linked to infestation and susceptibility to hemlock woolly adelgid (Homoptera: Adelgidae). Environmental Entomology 35:112-120.