Establishment, hybridization and impact of Laricobius predators on insecticide-treated hemlocks: Exploring integrated management of the hemlock woolly adelgid

Listen to a brief audio clip by author Albert (Bud) Mayfield describing this publication. • Text Transcript


An integrated management approach is needed to maintain eastern hemlock (Tsuga canadensis (L.) Carrière) in eastern North America and to minimize tree damage and mortality caused by the invasive hemlock woolly adelgid (Adelges tsugae Annand). This study examined the hypothesis that chemical control with low rates of insecticide and biological control can be combined in the same stand to impact adelgid populations, prolong crown health, and allow predator proliferation. Sixty T. canadensis trees in northern Georgia were individually treated via soil injection with 0%, 10%, or 25% of the label rate of imidacloprid insecticide, and the biological control predator Laricobius nigrinus Fender was released in the stand, two and four years later. By year seven, hemlocks treated with the 25% imidacloprid rate lost their insecticide protection, had significantly better crown health and higher adelgid densities than untreated trees, and supported as many Laricobius predator larvae as untreated trees. In year seven, no residues of imidacloprid were detected in Laricobius larvae feeding on previously-treated hemlocks. Most (77%) of the predators collected on study trees were identified as L. nigrinus, 12% were the native congener Laricobius rubidus LeConte, and 11% were hybrids between the introduced and native species. The hybridization rate remained stable over time. The density of undisturbed A. tsugae ovisacs was twice as high on branches protected from predators as compared with branches exposed to predators. Results suggest that chemical and biological control of A. tsugae can be successfully integrated to help prolong hemlock health, although additional predators may be necessary to protect hemlock trees in the southern Appalachians.

Sound Research audio clip of this publication is available.

  • Citation: Mayfield, Albert E. III; Reynolds, Barbara C.; Coots, Carla I.; Havill, Nathan P.; Brownie, Cavell; Tait, Andrew R.; Hanula, James L.; Joseph, Shimat V.; Galloway, Ashley B. 2014. Establishment, hybridization and impact of Laricobius predators on insecticide-treated hemlocks: Exploring integrated management of the hemlock woolly adelgid. Forest Ecology and Management 335 (2015). 10 p.
  • Keywords: Adelges tsugae, Biological control, Imidacloprid, Laricobius nigrinus, Olefin-imidacloprid, Tsuga canadensis
  • Posted Date: October 21, 2014
  • Modified Date: July 6, 2021
  • Print Publications Are No Longer Available

    In an ongoing effort to be fiscally responsible, the Southern Research Station (SRS) will no longer produce and distribute hard copies of our publications. Many SRS publications are available at cost via the Government Printing Office (GPO). Electronic versions of publications may be downloaded, printed, and distributed.

    Publication Notes

    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
    • Our online publications are scanned and captured using Adobe Acrobat. During the capture process some typographical errors may occur. Please contact the SRS webmaster if you notice any errors which make this publication unusable.
    • To view this article, download the latest version of Adobe Acrobat Reader.