In short:
Efforts to curb the spread of the shot-hole borer infestation destroying Australia’s urban canopy must ramp up before beetle activity escalates in the warmer months, experts say.
The pest is currently contained within a quarantine site in Perth, where upwards of 3000 trees have been destroyed.
What’s next?
Scientists want more research to be conducted into alternative management options, including chemical treatments.
Authorities are in a race against time to stop a tiny beetle from stripping Australia’s urban tree canopy, amid fears the pest could enter an “explosive phase” as spring approaches.
Native to South-East Asia, the polyphagous shot-hole borer is the size of a sesame seed and was first detected in Western Australia in 2021.
When coupled with a fungus, the pair can kill a tree within two years by blocking the flow of water between the roots and leaves,
Cost of damage unknown
The borer is believed to be contained in a quarantine zone in Perth, having destroyed more than 3,000 trees within it.
The spread of the pest is relatively slow in cooler weather, but if it manages to escape when breeding picks up in spring, it’s unknown what it will cost Australia.
The beetle is predicted to leave a $28 billion hole in South Africa’s economy over the next decade, and has also wreaked havoc on avocado, mango and macadamia trees in California and Israel.
Short window to stop pest
University of Western Australia associate professor of applied entomology Theo Evans is part of an advisory group assisting the Department of of Primary Industries and Regional Development (DPIRD) in its efforts to eradicate shot-hole borer.
He said there was an urgent need for action before the warm weather started, when the beetles are at their most active.
“Many scientists who work on invasions fear that we are entering the explosive phase,” Dr Evans said.
“We have a short opportunity of time to eradicate the beetle.”
He said current research had barely scratched the surface of possible treatment options.
“We’ve tested well under one per cent of the full range of [treatment] products. There is some way to go in deciding whether or not chemicals are effective or not,” Dr Evans said.
“We have several biocontrol options that are effective against a wide range of beetle species which are available in Australia now and nobody has tested those options.”
There have been signs of success elsewhere in the world, with researchers in California developing traps to attract and kill the borer in avocado orchards.
DPIRD deputy director general of biosecurity Mia Carbon said local scientists were meeting regularly and had developed priorities for the department to consider.
But despite the urgency to stop the beetle, Dr Evans said the advisory group has not met with the department in months.
“There are no [future] meetings organised,” he said.
‘We’re flying blind’
CSIRO principal research scientist Bruce Webber said a national cost-benefit analysis was needed to know whether a $41 million national eradication response over three years was enough.
“Until you actually quantify that, it’s really hard to justify how much to spend on an eradication program or how long to pursue eradication for if it’s proving challenging,” Dr Webber said.
Trees grown for timber are among those in the firing line, with ash, elm and oak trees included in the more than 400 targeted species.
Fig and plane trees are both victims and the borer has torn through popular attractions like Hyde Park and Kings Park in Perth — trees that are densely featured in other capital cities.
“If you look at the tree canopy cover across Sydney and Brisbane, figs are a much bigger feature than they are here,” Dr Webber said.
“Look at the cover of plane trees in Melbourne, if we lose all of those, those cities will be very different places.
“We are flying blind without knowing the full extent of the impact of this beetle.”
Hardline approach
DPIRD is spearheading the national eradication program with a hardline approach of pruning or removing host trees, which Ms Carbon said was the only proven way to kill the pest. .
“I’m very hopeful, as is everybody involved, that in the future that will change, and we will have other technologies available to us,” she said.
“We work nationally with all the national scientists and the chief plant biosecurity officers on the response plan, and in addition to that we’re working with local scientists with a WA scientific advisory group.
“But at the moment there have been no effective chemical treatments found anywhere in the world.”
‘Crying out to help’
Dr Evans warned it could be dangerous to take notes from other countries who have given up on eradicating the pest.
Authorities in California initially misidentified the borer and missed the window of opportunity to kill it off.
Dr Evans said the spread of the beetle in WA is relatively small so eradication is still feasible, but it would require a new approach.
“The little bit [DPIRD] told us suggests that they are repeating trials that have been done elsewhere and have not had a high mortality,” he said.
Dr Webber said the response effort must be collaborative.
“We’re crying out to help,” he said.
“Now is the time where we need critical action and we need to be deploying that at scale.”
Dr Webber said people on the ground in Perth could find innovative solutions to the shot-hole borer problem, given the resources.
“There’s huge potential to achieve something really ambitious here and we all need to be digging in,” he said.
“The impact for not achieving success in this space is too great to walk away from.”
