Polyphagous shot-hole borer

Current situation

The Western Australian Department of Primary Industries and Regional Development (DPIRD) is responding to detections of polyphagous shot-hole borer (Euwallacea fornicatus). The borer, which is a tiny beetle exotic to Australia, bores into living trees and can result in tree death. 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.

Infested trees are being removed or treated and more than 3,000 traps have been deployed to assist with surveillance activities.

DPIRD staff have inspected more than one million trees on over 25,000 properties as part of the surveillance program.

In Australia, the box elder maple (Acer negundo) is considered the main reproductive host and amplifier tree. Other key hosts for surveillance include maple (Acer), oak (Quercus), plane (Platanus), coral (Erythrina), avocado (Persea), locust (Robinia), fig (Ficus) and poplars (Populus) trees.

Movement restrictions in Western Australia

A Quarantine Area is in place across 21 local government areas - covering 623 square kilometres - to help contain the spread of the borer and allow for 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.

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 2mm 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 (referred to as a complex).

The fungus can colonise tissue of susceptible trees though it is likely the beetle and fungus complex, not the fungus alone, which kills susceptible trees.

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 are maple, oak, plane, coral tree, avocado and willows.

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 has become established, the removal and treatment of dead trees in urban areas has caused significant economic impacts.

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.

Government response

DPIRD continues to work closely with the local plant industries, councils, and the community to conduct the surveillance activities.

The Consultative Committee on Emergency Plant Pests (CCEPP) continues to meet in response to these detections and the National Management Group has approved a 3-year phased Response Plan for eradication of the polyphagous shot-hole borer complex. The plan is focused on:

  • removing infested reproductive host trees
  • managing infested non-reproductive trees
  • tracing and surveillance
  • compliance
  • community engagement.

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.