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Northern Research Station
One Gifford Pinchot Drive
Madison, WI 53726
(608) 231-9318
(608) 231-9544 TTY/TDD

Hemlock Woolly Adelgid

Genetics and Taxonomy of Laricobius

Research Issue

[photo:] Laricobius rubidus is native to eastern North America.Laricobius nigrinus is a predaceous beetle species native to western North America and has been released in eastern North America as a biological control of the hemlock woolly adelgid (HWA). In eastern North America there is a congeneric native species Laricobius rubidus that feeds on pine bark adelgid, Pineus strobi, and sometimes on HWA but without significant population impact. A phylogenetic analysis of the members of the genus Laricobius that feed on adelgids showed that L. nigrinus and L. rubidus are very closely related.

Our Research

We are using microsatellite markers to examine population genetic structure within and between L. nigrinus and L. rubidus. This will help us determine historical and current gene flow between the species.

Expected Outcomes

We will determine the amount of gene flow between the two species in areas where Laricobius nigrinus was released in the eastern U.S. The microsatellite markers can also be used to assess genetic variation in laboratory colonies and to target collection sites to best maintain colony diversity.

Research Results

Using DNA sequence data from both mitochondrial and nuclear DNA, we determined the phylogenetic relationships among the three Laricobius species native to North America, plus three Asian and one European species. Laricobius nigrinus from western North America and L. rubidus from eastern North America were very closely related. Using mitochondrial DNA sequence data, we developed a polymerase chain reaction restriction length polymorphism (PCR-RFLP) diagnostic assay to distinguish L. nigrinus from L. rubidus maternal lineages and efficiently track the establishment and spread of L. nigrinus after its release in eastern North America.

Using microsatellite markers, Laricobius nigrinus was found to be hybridizing with the native species, L. rubidus in sites where L. nigrinus was released and became established. On hemlock, there is mostly L. nigrinus with a lower proportion of hybrids and L. rubidus. On white pine, the opposite pattern was found, with mostly L. rubidus and fewer hybrids and L. nigrinus. Since L. nigrinus was more dominant on hemlock and L. rubidus was more dominant on white pine, this may demonstrate that each beetle species prefers a different habitat which could promote preservation of each pure species despite hybridization.

Fischer, M. J., N. P. Havill, C. C. Brewster, G. A. Davis, S. M. Salom, and L. T. Kok. 2015. Field assessment of hybridization between Laricobius nigrinus and L. rubidus, predators of Adelgidae. Biological Control 82: 1-6.

Mayfield, A. E. I., B. C. Reynolds, C. I. Coots, N. P. Havill, C. Brownie, A. R. Tait, J. L. Hanulaf, S. V. Joseph, and A. B. Galloway. 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: 1-10.

Jones, C. E., N. P. Havill, J. L. Hanula, and S. K. Bramans. 2014. Post release recovery of hemlock woolly adelgid predators in the North Georgia mountains. Journal of Entomological Science 49: 383-400.

Havill, N. P., G. Davis, D. L. Mausel, J. Klein, R. McDonald, C. Jones, M. Fischer, S. Salom, and A. Caccone. 2012. Hybridization between a native and introduced predator of Adelgidae: An unintended result of classical biological control. Biological Control 63: 359-369.

Davis, G. A., N. P. Havill, Z. N. Adelman, A. Caccone, L. T. Kok, and S. M. Salom. 2011. DNA barcodes and molecular diagnostics to distinguish an introduced and native Laricobius (Coleoptera: Derodontidae) species in eastern North America. Biological Control 58: 53-59.

Havill N, Klein J, Keena M, Caccone A. 2009. Characterization of microsatellite loci for Laricobius nigrinus and L. rubidus, predators of adelgids in North America. In: McManus, Katherine A; Gottschalk, Kurt W., eds. Proceedings. 20th U.S. Department of Agriculture interagency research forum on invasive species 2009; 2009 January 13-16; Annapolis, MD. Gen. Tech. Rep. NRS-P-51. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 76.

Research Participants

Principal Investigators

  • Nathan Havill, Research Entomologist, U.S. Forest Service, Northern Research Station
  • Adalgisa Caccone, Yale University, Department of Ecology and Evolutionary Biology

Last Modified: 05/08/2015

About this Research Area

Science theme: Forest Disturbance Processes

Science Topic: Invasive Species


About Hemlock Woolly Adelgid
Biological Control
Featured Publication

Havill N, Klein J, Keena M, Caccone A. 2009. Characterization of microsatellite loci for Laricobius nigrinus and L. rubidus, predators of adelgids in North America. In: McManus, Katherine A; Gottschalk, Kurt W., eds. Proceedings. 20th U.S. Department of Agriculture interagency research forum on invasive species 2009; 2009 January 13-16; Annapolis, MD. Gen. Tech. Rep. NRS-P-51. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 76.