Polyphagous Shot Hole Borer – A New Invasive Borer Found in WA

An invasive species of timber borer has been detected in Western Australia.

The polyphagous shot hole borer (PSHB; Euwallacea fornicatus), an invasive pest, has been detected in Perth, Western Australia. The tiny beetle is part of the ambrosia group of beetles (bark beetles and pinhole borers). However, it is not a pest of timber in service, but rather a major threat to live trees and of particular concern to the nursery, fruit and nut tree industries. As it attacks a wide range of trees (as its polyphagous name suggests), if it becomes established it could affect general amenity trees and have a significant environmental impact. Although not a pest of timber in service, pest managers have a role to play in helping in its detection to prevent establishment in Australia.

The polyphagous shot hole borer was first detected in east Fremantle (WA) in August of 2021 when a member of the public reported symptoms of dieback and dead branches in their maple tree.

Native to Southeast Asia, the small, dark brown/black beetle (pictured above) is around 2 mm long and the adult beetles bore into live trees. 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 poplar (Populus) trees.

One of the key aspects of its biology is that it has a symbiotic relationship with a Fusarium fungus, which it introduces to the trees. The fungus provides a food source for both the larvae and adult beetle. It is the Fusarium fungus that causes Fusarium dieback disease in trees, especially those already suffering from a large level of borer infestation.

 

Borer tunnels stained brown/black by the Fusarium fungus (photo credit: PIRD/Government of Western Australia)

 

As with any exotic pest incursion, the Western Australian Government is undertaking a massive surveillance program. Currently staff from the Department of Primary Industries and Regional Development (DPIRD) have inspected over 1.2 million trees on 35,000 properties. They are also using over 3,000 traps to aid with the monitoring program. Infested trees are removed and destroyed. Spring and autumn are when the beetle is most visible, when the newly mated female borers disperse to find new host trees.

The government has also set up a quarantine area across 21 local government areas – covering 623 square kilometres – to help contain the spread of the borer and focus surveillance activities. A communication program is in place to educate the public in what to look for and make them aware of the restriction on the movement of plants and timber that apply to the quarantine area. Anyone living or working in the quarantine area cannot move any bark, potted plants, firewood, tree prunings, logs, plant cuttings, mulch, timber, wood or wood chips above a certain size outside of the area.

 

Characteristic pinhole damage caused by a shot
hole borer (photo credit: DPIRD/Government of Western Australia)

 

As pest managers are regularly out and about visiting properties, their expert knowledge will be useful in detecting potential infestations on properties they visit. Although the obvious symptoms of a well-developed infestation are wilting and dieback of tree branches and leaves, often starting in the upper canopy, a number of signs of infestation can be picked up by inspecting the tree trunks:

  • Multiple entrance holes on the trunk or branches that are up to 2 mm or the size of the tip on a ballpoint pen
  • Frass (powdery substance) extruding from the tree and/or crystalline foam that looks like sugar volcanoes exuding from the entry holes
  • Thick resin or sap on the tree branches or trunk (which can sometimes push the beetle out of the gallery)
  • Dark brown to black staining of the wood around entrance holes.

 

Sugar volcanos are a typical symptom around borer exit holes (photo credit: FABI/University of Pretoria)

 

It is important that all pest managers are aware of this issue, not only those who operate in Perth or WA. As this is the first detection of PSHB in Australia, other states and jurisdictions are on alert for this exotic pest. Through the combined effort of surveillance, trapping, tree management and quarantine restrictions, together with public information, every effort is being made to contain the spread of PSHB in WA. Early detection is key to preventing PSHB spread and establishment and observant pest managers can offer valuable help.

It is important for pest managers to report suspected borer damage via the MyPestGuide app or by calling the Exotic Plant Pest Hotline on 1800 084 881. This provides valuable surveillance data and helps to inform nationally coordinated response actions.

Choose Your Country or Region

Asia Pacific