Agriculture: Avocado Pest Management Guidelines

Polyphagous Shot Hole Borer and Kuroshio Shot Hole Borer

  • Euwallacea spp.
  • Description of the Pest

    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.

    Damage

    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.

    Management

    Early detection of infestations and removal of the infested branches will help reduce beetle numbers and therefore, also reduce the spread of the fungus.

    • Chip infested wood onsite to a size of one inch or smaller. If the branch is too large to chip, solarize them under a clear tarp for several months
    • Avoid movement of infested firewood and chipping material out of infested area
    • For more informationvisit the UC Riverside Eskalen Lab website.

    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:

    (* species known to be susceptible to Fusarium dieback)

    • acacia (Acacia spp.)
    • American sweet gum (Liquidambar styraciflua)*
    • avocado (Persea americana)*
    • bigleaf maple (Acer macrophyllum)*
    • black cottonwood (Populus trichocarpa)
    • Black Mission fig (Ficus carica)
    • blue palo verde(Cercidium floridum)*
    • box elder (Acer negundo)*
    • brea (Cercidium x sonorae)*
    • Californiasycamore(Platanus racemosa)*
    • camellia(Camellia semiserrata)*
    • castor bean (Ricinus communis)*
    • Chinese holly(Ilex cornuta)*
    • coast live oak (Quercus agrifolia)*
    • coral tree(Erythrina corallodendron)*
    • cork oak (Quercus suber)*
    • Engelmann oak (Quercus engelmannii)
    • English oak (Quercus robur)*
    • evergreen maple (Acer paxii)*
    • Fremont’s cottonwood (Populus fremontii)
    • Goodding's black willow (Salix gooddingii)
    • Japanese beech (Fagus crenata)
    • Japanese maple (Acer palmatum)*
    • Japanese wisteria (Wisteria floribunda)*
    • Kurrajong (Brachychiton populneus)
    • London plane (Platanus x acerifolia)
    • mesquite amargo (Prosopis articulata)
    • Mexican sycamore (Platanus mexicana)
    • Moreton Bay chestnut (Castanospermum australe)*
    • palo verde (Parkinsonia aculeata)*
    • Persian silk tree(Albizia julibrissin)*
    • red flowering gum (Corymbia ficifolia)
    • red willow (Salix laevigata)
    • titoki (Alectryon excelsus)*
    • tree of heaven (Ailanthus altissima)
    • trident maple (Acer buergerianum)*
    • valley oak (Quercus lobata)*
    • weeping willow(Salix babylonica)
    • white Alder (Alnus rhombifolia)

    Known suitable reproductive host trees of Kuroshio shot hole borer:

    (* species known to be susceptible to Fusarium dieback)

    • arroyo willow (Salix lasiolepis)
    • avocado (Persea americana)*
    • black poplar (Populus nigra)
    • black locust (Robinia pseudoacacia)
    • black willow (Salix nigra)
    • California sycamore (Platanus racemosa)*
    • castor bean (Ricinus communis)*
    • coast live oak (Quercus agrifolia)*
    • cork oak (Quercus suber)*
    • dwarf coral tree (Erythrina humeana)*
    • Fremont's cottonwood (Populus fremontii)
    • Persian silk tree (Albizia julibrissin)*
    • red willow (Salix laevigata)
    • strawberry snowball tree (Dombeya cacuminum)*
    Text Updated: 12/17