Polyphagous shot-hole borer

Current situation

The WA Department of Primary Industries and Regional Development (DPIRD) is currently responding to detections of polyphagous shot-hole borer (Euwallacea fornicatus). The borer is a tiny beetle which is exotic to Australia.  

The first detection was made in East Fremantle, WA in August 2021 when a member of the public reported symptoms of dieback and dead branches in their maple tree.

DPIRD’s sampling and laboratory testing detected the suspect borer, with confirmatory diagnostics completed by the Queensland Department of Agriculture and Fisheries.

A Quarantine Area is in place across 17 local government areas to prevent further spread of the pest and allow for urgent surveillance activities.

To date, positive samples have been taken from numerous species of trees including: box elder maple, coral tree, sophora, poinciana, mango and sea hibiscus.

The Consultative Committee on Emergency Plant Pests (CCEPP) met in October and November 2021 to discuss this detection. It was recommended that the polyphagous shot-hole borer and the fungus associated with it, are emergency plant pests as defined by the Emergency Plant Pest Response Deed. The committee agreed that more information is needed in terms of its current distribution, before they can make a recommendation on the technical feasibility of eradication.

DPIRD is working closely with the local plant industries, councils, and the community to conduct the surveillance and tracing activities recommended by CCEPP.

About polyphagus shot-hole borer

The polyphagous shot-hole borer is a tiny beetle that bores into living trees which can result in tree death. It is considered both an agricultural and environmental pest with more than 400 host species including horticulture production, native and amenity trees.

The adult female beetle is 2 millimetres long and tunnels into the tree’s stems and branches, causing damage and dieback.

The polyphagous shot-hole borer has a symbiotic relationship with the Fusarium fungus, which is used as a food source for the beetle and its larvae.

The fungus disrupts water and nutrient movement within the vascular system of susceptible trees, causing the disease Fusarium dieback. Symptoms are wilting and dieback of tree branches and leaves, often starting in the upper canopy.

The borer spreads with the movement of infested trees, firewood, and green waste material.

After mating, female borers disperse to look for suitable host trees and may fly up to 400 metres. Spring and autumn are when the beetle is most likely to be seen, when it moves to new trees.

Trees in which the beetle can breed and multiply (referred to as reproductive host trees) are maple, oak, plane, coral tree, avocado and willows.

Eucalyptus, citrus, and olive trees are considered non-reproductive host trees. This means that the beetle will attack the tree but it doesn’t establish tunnels (also called galleries). And the beetle does not breed in these trees.

If the borer spreads beyond urban amenity trees, it could impact the nursery, fruit, and nut tree industries. It may also have potential impacts on the forestry industry.

In South Africa where it is has established, the removal and treatment of dead trees in urban areas has caused significant economic impacts.

Movement restrictions in Western Australia

A Quarantine Area Notice is in place across 17 local government areas to help contain the spread of the borer and allow for urgent surveillance activities.

Anyone living or working in the Quarantine Area cannot remove any bark, potted plants, firewood, tree prunings, logs, plant cuttings, mulch, timber, wood or wood chips above a certain size outside of the Quarantine Area.

The polyphagous shot-hole borer does not affect grass, so lawn clippings can be disposed of as normal.

A detailed map of the quarantine area is available at on the DPIRD website.

What to look for

The adult beetles and their larvae can be hard to spot as they spend most of their lives inside a tree, however, there are several signs that indicate the borer could be present including:

  • multiple entrance holes on the trunk or branches that are up to 2 millimetres or the size of the tip on a ballpoint pen
  • frass (powdery substance) extruding from the tree and crystalline foam which look like sugar volcanoes exuding from the entry holes
  • thick resin or sap on the tree’s branches or trunk – this can sometimes push the beetle out of the gallery
  • dark brown to black staining of the wood around entrance holes
  • wilting and dying branches and eventually tree death. Symptoms usually start in the upper canopy.

Spring and autumn are when the beetle is most visible.

Polyphagus shot-hole borer in a maple tree.  Photo courtesy P Scanlon DPIRD, WA.
Polyphagus shot-hole borer in a maple tree. Photo courtesy P Scanlon DPIRD, WA.
Exit holes in a tree created by polyphagus shot-hole borer. Photo courtesy P Scanlon DPIRD, WA.
Exit holes in a tree created by polyphagus shot-hole borer. Photo courtesy P Scanlon DPIRD, WA.

Report sightings

Residents and people working in the affected areas are encouraged to check their trees for signs of borer damage and wilting.

If you see any signs of the polyphagous shot-hole borer in trees or plant material, keep the material on your property and report it immediately to DPIRD through their MyPestGuide Reporter app or phone the Exotic Plant Pest Hotline on 1800 084 881.

More information

Visit the DPIRD website to get more information about the polyphagous shot-hole borer. Their website has more detailed photos, maps of the restricted areas and information about their response activities.