The polyphagous shot-hole borer (Euwallacea fornicatus) is a destructive, invasive beetle threatening trees in Australia. Originally from parts of Southeast Asia, this tiny pest was first detected in Western Australia in 2021 and has quickly become a serious concern for urban landscapes, parks, and gardens.
Despite being only 2 mm long, this beetle can cause significant damage by boring into trees and introducing harmful fungi that disrupt the tree’s ability to transport water and nutrients.
What Is the Polyphagous Shot-Hole Borer?
The polyphagous shot-hole borer (PSHB) is a type of ambrosia beetle that tunnels into tree trunks and branches to cultivate a symbiotic fungus, Fusarium euwallaceae, which it relies on for food. Unfortunately, this fungus blocks the tree’s vascular system, leading to branch dieback, canopy thinning, and even death in susceptible trees.
This beetle is highly polyphagous, meaning it targets a wide range of tree species — over 100 known hosts — including:
- Plane trees (Platanus)
- Maple (Acer)
- Oak (Quercus)
- Avocado (Persea)
- Coral trees (Erythrina)
Where Do Polyphagous Shot-Hole Borers Live?
Native Range — Southeast Asia
In Southeast Asia, the polyphagous shot-hole borer naturally occurs in:
- Thailand
- Vietnam
- Malaysia
- Indonesia
- Sri Lanka
- India
In these countries, it typically targets weakened or dead trees, where natural predators help keep its population under control.
Invasive Range — Australia
The beetle was first identified in East Fremantle, Western Australia, in August 2021. It has since spread through nearby Perth suburbs. The Perth metropolitan area, with its warm climate and variety of host trees, has provided an ideal environment for the beetle’s establishment.
While currently contained within parts of Western Australia, there is a significant risk of spread to other warm, coastal regions of the country, including:
- Southwest Western Australia
- Northern New South Wales
- Southeast Queensland
- Coastal Victoria and South Australia
How to Spot the Polyphagous Shot-Hole Borer
Early detection is critical. Signs to watch for include:
- Tiny, perfectly round entry holes (1–2 mm in diameter)
- Sawdust-like frass (fine wood dust) near holes or at the base of trees
- Sticky, sugary ooze leaking from entry points
- Branch dieback or canopy thinning in otherwise healthy trees
If you notice these symptoms, it’s important to contact your local biosecurity authority immediately.
How to Protect Trees in Australia
To minimise the impact of the polyphagous shot-hole borer, use a combination of the following tree protection strategies:
- Surveillance and Early Detection
Inspect susceptible trees regularly, especially in urban landscapes, streets, and parks. Immediate reporting helps prevent wider spread. - Movement Restrictions
Avoid transporting wood, green waste, mulch, firewood, or pruned branches from infested areas to other regions. These materials can easily carry beetles and fungal spores. - Tree Removal and Disposal
Infected trees or branches may need to be removed and destroyed — usually through chipping, deep burial, or incineration. This prevents beetles from spreading to new areas. - Chemical Treatments
Chemical control options are currently limited, and primarily used on high-value or heritage trees. Some systemic insecticides and fungicides may help reduce infestations, but should always be applied by certified professionals. - Host Plant Management
Where practical, limit or replace highly susceptible tree species in urban plantings and streetscapes. This reduces available breeding sites and helps slow the beetle’s spread.
The Final Word: “Bore No More!”
The polyphagous shot-hole borer might be small, but its impact on Australian trees is enormous. With early detection, smart tree management, movement control, and careful surveillance, it’s possible to protect both urban and natural tree populations from this invasive pest.
If you’re interested in broader threats to forests, check out our articles on invasive species for more information on how other non-native pests and plants can disrupt ecosystems.
Staying alert and taking proactive steps now is the best way to avoid long-term damage. Don’t let your trees become the next victims of this tiny tunneler.