How to Manage Pests
UC Pest Management Guidelines
Polyphagous Shot Hole Borer and Kuroshio Shot Hole Borer
Scientific name: Euwallacea spp.
(Reviewed 9/16, updated 12/17)
In this Guideline:
Description of the pests
Polyphagous shot hole borer (PSHB) and Kuroshio shot hole borer (KSHB) are genetically different invasive species, but morphologically they are indistinguishable. Females are black and 0.07 to 1.0 inch (1.8–2.5 mm) long. Males are brown and smaller than females at 0.06 inch (1.5 mm) long. The female tunnels into a wide variety of host trees forming galleries, where it lays its eggs. More females are produced than males. Mature siblings mate with each other so that females leaving to start their own galleries are already pregnant. Males do not fly, but stay in the host tree.
Both beetle species have a special structure in their mouth called a mycangium with its own novel symbiotic fungal species. Polyphagous shot hole borer carries three fungi: Fusarium euwallaceae, Graphium euwallaceae and Paracremonium pembeum. Kuroshio shot hole borer carries two different species for fungi: Fusarium sp. and Graphium sp. The beetle grows these fungi in their galleries. The fungi cause FUSARIUM DIEBACK disease, which interrupts the transportation of water and nutrients in the host tree.
A host tree's visible response to a beetle's attack varies among host species. Staining, sugary exudate (also called a sugar volcano), gumming, and frass may be noticeable before the tiny beetles are found. The beetle's entry and exit holes, which are about 0.03 inch (0.85 mm) in diameter, can be located beneath or near the symptoms. The abdomen of the female beetle can sometimes be seen sticking out of the hole, guarding the developing larvae. Advanced fungal infections will eventually lead to branch dieback.
Rapid spread of the beetle and fungi throughout various land-use areas is attributed to the diverse range and quantity of suitable hosts in Southern California.
Early detection of infestations and removal of the infested branches will help reduce beetle numbers and therefore, also reduce the spread of the fungus.
KNOWN REPRODUCTIVE HOSTS OF POLYPHAGOUS SHOT HOLE BORER AND KUROSHIO SHOT HOLE BORER
Polyphagous shot hole borer attacks hundreds of tree species, but it can only successfully lay its eggs and grow the fungi in certain hosts.
Known suitable reproductive host trees of polyphagous shot hole borer:
Known suitable reproductive host trees of Kuroshio shot hole borer:
UC IPM Pest Management Guidelines:
A. Eskalen, Plant Pathology, UC Riverside
Acknowledgment for contributions to Invertebrates:P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura County
M. Blua, Entomology, UC Riverside
P. Oevering, UC Cooperative Extension, Ventura County
D. Machlitt, Consulting Entomology Services, Moorpark, CA
T. Roberts, Integrated Consulting Entomology, Ventura, CA
B. B. Westerdahl, Nematology, UC Davis