Invasive Shot Hole Borers
Invasive Shot Hole Borers
Invasive Shot Hole Borers
University of California
Invasive Shot Hole Borers

Look-alikes

The first step to managing PSHB is identifying the insect. Unfortunately, many other pests and diseases cause similar symptoms on the same host trees. For example, dark staining is frequently reported on Tipu tree (Tipuana tipu), but it is rarely positive for PSHB because an entry-hole is often absent.

Do these scenarios apply to the symptoms you see? If so, consider these lookalike pests, diseases, and conditions:

Staining, exudate, or frass without entry-hole Entry-hole is not round Entry-hole bigger than ball-point pen tip Entry-hole smaller than ball-point pen tip

Some trees are host to many common PSHB lookalikes. If examining one of these species, consider its other pests and diseases:

Pest Profiles

Western oak bark beetle may vector the Foamy bark canker disease (Jack Kelly Clark / UC IPM)

Western oak bark beetle may vector the Foamy bark canker disease (Jack Kelly Clark / UC IPM)

Western oak bark beetle and Foamy bark canker

Pseudopityophthorus pubipennis and Geosmithia species #41 (fungus)

Host trees: Coast live oak

Beetle size: 1.7-2.3 mm long

Entry-hole: Smaller than PSHB

Symptoms: Beetle produces light-colored frass and light staining; symptoms of disease include wet discoloration of bark, reddish sap and/or foamy liquid oozing from entry-hole, and dead wood around the entry-hole beneath the bark

Note: The beetle is native to California and typically attacks stressed or dying oaks; some of the beetles vector the Foamy bark canker disease, which was discovered relatively recently. See the UC ANR pest alert for more information.


Native to Europe, Fruittree bark beetle has become common throughout most of the United States (Jack Kelly Clark / UC IPM)

Native to Europe, Fruittree bark beetle has become common throughout most of the United States (Jack Kelly Clark / UC IPM)

Fruit tree bark beetle

Scolytus rugulosus

Host trees: Many deciduous fruit and nut trees, including stone fruits, apples, almonds

Beetle size: Beetle: 2-2.5 mm long

Entry-hole: Larger than PSHB

Symptoms: Copious gumming, oozing sap, or frass from entry-hole; tend to bore galleries close to bark surface


Monarthrum scutellare typically attacks stressed trees (Jack Kelly Clark / UC IPM)

Monarthrum scutellare typically attacks stressed trees (Jack Kelly Clark / UC IPM)

Monarthrum oak ambrosia beetles

Monarthrum dentiger, Monarthrum scutellare

Host trees: Oak species, tanoak, California buckeye; usually attacks trees that are already stressed by other pests or conditions

Beetle size: 3.5-4.1 mm (M. scutellare) or 1.9-2.44 mm (M. dentiger) long

Entry-hole: Larger than PSHB

Symptoms: Bleeding, frothing, white boring dust from entry-hole


Xyleborus saxeseni mainly attacks stressed or dying trees (Cristoph Benisch / www.kerbtier.de)

Xyleborus saxeseni mainly attacks stressed or dying trees (Cristoph Benisch / www.kerbtier.de)

Lesser shothole borer

Xyleborinus saxeseni

Host trees: Stressed or dying trees

Beetle size: 1.7-2.3 mm long

Entry-hole: Smaller than PSHB

Symptoms: Reddish frass and/or sap; wet staining and/or dead tissue around entry-hole


Rough bark and reddish frass produced by western sycamore borer (John Kabashima / UC Cooperative Extension)

Rough bark and reddish frass produced by western sycamore borer (John Kabashima / UC Cooperative Extension)

Western sycamore borer

Synanthedon resplendens

Host trees: Sycamore species (Platanus spp.), oak species (Quercus spp.), Ceanothus

Larva size: 25-38 mm long

Entry-hole: Larger than PSHB, irregular shape

Symptoms: Roughened bark, reddish frass and/or larvae pupal cases caught in bark crevices

Note: Most trees can tolerate extensive boring by this common native insect, and management is usually unnecessary


Characteristic D-shaped entry-holes of Gold-spotted oak borer (Tom Coleman / US Forest Service)

Characteristic D-shaped entry-holes of Gold-spotted oak borer (Tom Coleman / US Forest Service)

Gold-spotted oak borer

Agrilus auroguttatus

Host trees: Coast live oak, Canyon live oak, California black oak

Beetle size: ~10 mm long

Entry-hole: less than 4 mm wide, characteristic D-shape

Symptoms: Red or black staining running down bark, blistering and oozing on bark surface, crown thinning, twig and branch die-back

Resources: gsob.org


Discolored cavity beneath the bark of a tree infected with Xanthomonas campestris (Akif Eskalen / UC Riverside)

Discolored cavity beneath the bark of a tree infected with Xanthomonas campestris (Akif Eskalen / UC Riverside)

Xanthomonas campestris (pathogenic bacteria)

Host trees: Many, including avocado

Entry-hole: No entry-hole, but a long, deep cavity is often present

Symptoms: Exudate and bleeding (reddish on avocado) from cavity in the bark


Physical injury

Many trees respond to PSHB attacks the same way that they react to other kinds of damage: by producing staining, gumming, or exudate. Be aware of any recent management activity on the suspected tree, and look for entry-holes of the typical PSHB size and shape to avoid a misidentification of tree symptoms.

Sources of injury: pruning cuts, injections sites, staples (often used to hang strings of lights around trunk/branches), nails, other mechanical damage

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