Biological Invasions

, Volume 20, Issue 8, pp 2141–2155 | Cite as

Reproduction and potential range expansion of walnut twig beetle across the Juglandaceae

  • Andrea R. HeftyEmail author
  • Brian H. Aukema
  • Robert C. Venette
  • Mark V. Coggeshall
  • James R. McKenna
  • Steven J. Seybold
Original Paper


Biological invasions by insects that vector plant pathogens have altered the composition of natural and urban forests. Thousand cankers disease is a new, recent example and is caused by the complex of walnut twig beetle, Pityophthorus juglandis, and the fungus, Geosmithia morbida, on susceptible hosts, notably some Juglans spp. and Pterocarya spp. Host colonization by P. juglandis may be particularly important for disease development, but the beetle’s host range is not known. In the United States and Italy, this insect has expanded its geographic range by colonizing naïve hosts. The objective of this study was to characterize limits to, and variation within, the host range of P. juglandis and infer the extent to which hosts might constrain the geographic distribution of the insect. We examined colonization and reproduction by P. juglandis in no-choice laboratory experiments with 11 Juglans spp., one Pterocarya sp., and two Carya spp. over 2 years and found that all but the Carya spp. were hosts. Reproduction was generally greater on Juglans californica, J. hindsii, and J. nigra, than on J. ailantifolia, J. cathayensis, J. cinerea, J. major, J. mandshurica, J. microcarpa, or J. regia. Escape of an insect vector into populations of evolutionary-naïve hosts can facilitate rapid range expansion by the pest and massive mortality to hosts. Multi-continental plantings of suitable species may facilitate geographic range expansion of P. juglandis and place other, native Juglans spp. at risk.


Host-range expansion Host suitability Pityophthorus juglandis Thousand cankers disease Juglans 



We thank Charles Leslie, Department of Plant Sciences, University of California, Davis, CA; John Preece, USDA ARS NCGR, Davis, CA; Andrew D. Graves and James Jacobs, USDA Forest Service Forest Health Protection, Albuquerque, NM; Minnette Marr, Lady Bird Johnson Wildflower Center, Austin, TX; and the University of Minnesota Landscape Arboretum, Chaska, MN for assistance with procuring host material for testing. We thank Cliff Beumel, Director of Product Development, Sierra Gold Nurseries, Yuba City, CA for access to a commercial walnut seed orchard for collection of walnut twig beetles; J. Preece for access to the USDA ARS NCGR for the same purpose; and University of Minnesota undergraduate research assistants, Joe Pohnan and Collin Smith. We also thank Carlos H. Crisosto and Sebastian S. Silva (both Department of Plant Sciences, University of California, Davis) for providing information on walnut production in South America. We greatly appreciate the staff at the MDA/MAES Plant Growth Facility for support with biocontainment. Funding was provided by the NSF-IGERT Risk Analysis of Introduced Species and Genotypes program at the University of Minnesota (DGE-0653827) and a USDA-Forest Service Special Technology Development Program grant (R2-2012-01) that was administered by Jeffrey Witcosky and Stephanie Stephens, USDA Forest Service, Lakewood, CO. Participation of MVC and SJS in this project was coordinated and supported by USDA National Institute of Food and Agriculture, Specialty Crops Research Initiative Program Project (11684658), “Development of Disease-resistant Walnut Rootstocks: Integration of Conventional and Genomic Approaches.”

Author Contributions

ARH, RCV, BHA, MVC, JRM, and SJS all contributed to the experimental design of host assays. ARH performed all assays. ARH, BHA, and RCV analyzed the data. SJS, MVC, and JRM provided host material. SJS provided insects. ARH, BHA, RCV, and SJS wrote the manuscript; other authors provided editorial advice.

Supplementary material

10530_2018_1692_MOESM1_ESM.docx (21 kb)
Supplementary material 1 (DOCX 20 kb)


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Copyright information

© This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply [2018] 2018

Authors and Affiliations

  1. 1.Department of EntomologyUniversity of MinnesotaSt. PaulUSA
  2. 2.USDA Forest Service Northern Research StationSt. PaulUSA
  3. 3.The Center for AgroforestryUniversity of MissouriColumbiaUSA
  4. 4.Hardwood Tree Improvement and Regeneration CenterUSDA Forest ServiceWest LafayetteUSA
  5. 5.USDA Forest Service Pacific Southwest Research StationDavisUSA
  6. 6.Forest Health Protection, Southern CA Shared Service AreaUSDA Forest ServiceSan BernardinoUSA

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