Polyphagous Shot Hole Borer

The Polyphagous Shot Hole Borer, Euwallacea sp., is a boring beetle from the same family as bark and ambrosia beetles. PSHB is a non-native species originating from South East Asia, and was identified in2003 in Los Angeles County. Over 130 species of tree are susceptible to attack from PSHB, but the severity of injury can vary from single branch dieback to entire tree death. However, the PSHB can complete its life cycle in only about 20 tree species. Trees are not killed directly by the boring of the beetle, but by the symbiotic fungus the beetle carries with it, Fusarium euwallaceae. The fungus clogs the conductive tissues of the tree cutting off the flow of water and nutrients to the tree.

Treatment Strategy

Treatment can be tricky since the PSHB does not directly feed on the tree; rather, it feeds on the fungus grown in the galleries. This makes systemic insecticides ineffective and the results unreliable. Bark sprays have been seen to have the best results teamed with a fungicide to control already infected trees, or in preventing attacks on trees.

Trunk/Limb Spray Using Tengard

Signs of Damage

  • Symptoms can vary depending on the host tree
  • Check for entry holes about 0.03” wide (about size of pen tip) from the upper canopy of the tree to the trunk at eye level
  • Sometimes you can still see the abdomen of the female protruding from the hole
  • Early detection is best detected by vascular wilt symptoms, such as branch dieback, and staining of the wood around the entry holes
  • Other symptoms include: wet staining on bark from leaking xylem fluid, white powdery exudate (sometimes referred to as sugar volcanoes), and frass (sawdust)

Photo: Eskalen Lab, UC Riverside

Photo: Entomology Today

Photo: Natural History of Orange County, California

Trees At Risk

  • Avocado (Persea americana)
  • Big leaf maple (Acer macrophyllum)
  • Box elder (Acer negundo)
  • California sycamore (Platanus racemosa)
  • Castor bean (Ricinus communis)
  • English oak (Quercus robur)
  • London plane (Platanus x acerifolia)
  • Red willow (Salix laevigata)

Biology

  • Ambrosia refers to the symbiotic fungus the beetle carries with it and lines its galleries with, Fusarium euwallacea, which causes a disease in trees called Fusarium dieback.
  • The beetle is very small, measuring at about 0.07” –0.10” long and anywhere from brown to black in color.
  • The female beetle bores into susceptible trees lining the galleries with the spores of the Fusarium fungus.
  • After about 8 days the female lays her eggs in a pile at the end of the gallery.
  • The larvae hatch after a few days and begin to feed on the fungus spores in the gallery.
  • The larvae pupate and become adults after about a month.
  • Males from the same offspring mate with the females, and once inseminated the female leaves to find new host and create her own boring galleries.
  • PSHB can have multiple generations in a year.

References

Akif Eskalen. Kabashima, John. Dimson, Monica. (2016). Polyphagous Shot Hole Borer and Fusarium Dieback Field Guide [Brochure]. CA: Author.

University of California
http://ucanr.edu/sites/socaloakpests/Polyphagous_Shot_Hole_Borer/

Richard Stouthamer. The Polyphagous Shot Hole Borer, Euwallacea fornicatus, a New Invasive Pest in Southern California [Powerpoint]. Department of Entomology, University of CA, Riverside

http://caforestpestcouncil.org/wp-content/uploads/2008/07/Polyphagous-Shot-Hole-Borer.pdf

University of California Riverside
http://cisr.ucr.edu/polyphagous_shot_hole_borer.html

United States Department of Agriculture
http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5441594.pdf

A Treatment Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments by forestryimages.org

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