24-06-2025
Shot-hole borer's spread into Western Australia's forests 'inevitable', experts say
Biosecurity experts say it is only a matter of time until the invasive polyphagous shot-hole borer breaks quarantine lines in metropolitan Perth and spreads throughout the state.
The invasive beetle has already had a devastating impact on Perth's urban tree canopy, felling thousands of trees.
It is feared the effects could be replicated in the native forests of Western Australia's South West.
The WA government last week announced it efforts to eradicate the polyphagous shot-hole borer had failed.
It has changed its strategy from eradication, to management.
It has since poured an additional $26.5 million into its shot-hole borer response, which includes the continuation of two quarantine zones in Perth for at least 18 months.
The shot-hole borer is less than two millimetres long and spreads a fungus that can starve trees of nutrients, killing them in the process.
Experts are unsure how the pest arrived in the country.
Jacquie Rusha, who manages a native plant nursery in Bunbury, said biosecurity would become increasingly important as the beetle spread.
"It was inevitable that they were going to have to accept that it wasn't going to be contained," Ms Rusha said.
The nursery specialises in propagating and growing local native species for retail and landscaping projects.
Plants are grown onsite and are only shipped to the site under strict quarantine protocols.
However, Ms Rusha said she was concerned about the unknown impacts on the native environment as a whole.
"If we were to come across an infestation here, we would be able to quarantine immediately and find it a lot sooner than we would in the wild," she said.
"We don't know how this will all end up looking in the end, but we might lose some of those really key species of plants, particularly marri.
"This change in management certainly doesn't mean that we give up and go, 'oh well, it's just here now'.
"It means that if anything, we become more vigilant."
Introduced species of trees, including the box elder maple and coral tree, are extremely susceptible to the shot-hole borer.
But many Australian natives are also at high risk, including the Moreton bay fig, marri and red flowering gum.
Invasive Species Council policy director Carol Booth said 15 native tree species in WA had already been identified as highly or very highly susceptible to the pest.
"Now that eradication is off the table, the priority must be stopping the borer from spreading beyond the Perth region," Dr Booth said.
Ecologist Bruce Webber said the breach of containment lines in Perth was "inevitable" due to the eventual shift from cost-sharing between state and federal governments to just state funding.
The WA government said the quarantine zones would be maintained for the next 18 months as authorities transitioned to management of the pest.
"After that period, the federal and state cost-sharing model disappears, and this simply then becomes yet another invasive species added to the very long list that are being managed and funded at the state level," Dr Webber said.
What was less certain was the impact the beetle would have on the environment once it arrived.
"It's simply going to be a matter of suck it and see, and that's a pretty scary outcome given we know there are already impacts identified to our native species," Dr Webber.
"We don't know the full extent of the species that will be impacted as the borer inevitably spreads out to these native landscapes," Dr Webber said.
"But if it's anything to go by from what we've seen in Perth, there's serious concerns for how our native landscapes will be impacted in the long term.
"We're essentially flying blind as this beetle moves into our native landscapes."
Federal Agriculture Minister Julie Collins has been contacted for comment.
