Biological Invasions

, Volume 1, Issue 2, pp 247–254

Reshaping the Ecology of Invading Populations of Hemlock Woolly Adelgid, Adelges tsugae (Homoptera: Adelgidae), in Eastern North America

  • Mark S. McClure
  • Carole A.S.-J. Cheah

DOI: 10.1023/A:1010051516406

Cite this article as:
McClure, M.S. & Cheah, C.AJ. Biological Invasions (1999) 1: 247. doi:10.1023/A:1010051516406


Hemlock woolly adelgid, Adelges tsugae Annand (Homoptera: Adelgidae), is native to Japan where it is an innocuous inhabitant of Tsuga diversifolia Masters and T. sieboldii Carriere throughout their natural growing areas. Native adelgid populations are regulated by host resistance and natural enemies, in particular the oribatid mite, Diapterobates humeralis (Hermann) and the coccinellid beetle, Pseudoscymnus tsugae Sasaji and McClure. Invading populations of A. tsugae in western North America on T. heterophylla Sargent and T. mertensiana Carriere are mainly regulated by host resistance. However, invading populations in eastern North America attain damaging levels on T. canadensis (L.) Carriere and T. caroliniana Engelmann and are regulated mainly by weather and negative density-dependent feedback mechanisms related to host deterioration. Although A. tsugae is only passively dispersed by wind, birds, forest-dwelling mammals and humans, it is spreading at an alarming rate and is sufficiently cold hardy to threaten the existence of the two eastern hemlock species throughout their natural ranges. The current hope for suppressing invading populations of hemlock woolly adelgid in eastern North America lies with the exotic predator, P. tsugae. Extensive laboratory studies of the biology and predatory ability of P. tsugae revealed that it feeds on all life stages of its prey, that its multivoltine life cycle is well synchronized with that of the adelgid, and that it has great potential for biological control. We have reared and released nearly 130,000 adults of P. tsugae in forests in Connecticut, New Jersey and Virginia during the past four years. P. tsugae has reproduced, dispersed, overwintered and reduced densities of hemlock woolly adelgid by 47–88% in only five months on release branches at these sites. Current studies are investigating the long-term ability of P. tsugae to regulate invading populations of A. tsugae in eastern North America.

Adelges tsugaebiological controlDiapterobates humeralishemlockJapannatural enemiesPicea spp.population dynamicspredatorsPseudoscymnus tsugaeTsuga spp.

Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • Mark S. McClure
    • 1
  • Carole A.S.-J. Cheah
    • 1
  1. 1.Valley LaboratoryThe Connecticut Agricultural Experiment StationWindsorUSA (e-mail