A new Curtin University study warns that large parts of Australia, including major cities and farming regions, could be highly vulnerable to a fast-spreading invasive beetle, already causing severe damage across the Perth metropolitan area.
The study looked at the full life cycle of the polyphagous shot hole borer (PSHB), a tiny insect which releases a fungus that can starve trees of nutrients, killing them in the process. The study resulted in a model to analyse where new outbreaks are most likely to occur in Australia.
Researchers combined daily climate data, vegetation maps and biological parameters to predict where the beetle can survive, grow and spread.
The research found the destructive pest thrives in many Australian climates, and several other states like Queensland and New South Wales are at high risk of future PSHB infestations.
Lead author Dr Andrew Coates, from Curtin's School of Molecular and Life Sciences, said the modelling showed the PSHB was capable of extremely rapid population growth and could spread far beyond its current range in Perth, if not tightly contained.
"Our modelling shows that the east coast in particular offers ideal conditions for this beetle to establish and grow," Dr Coates said.
"The biggest risk is the beetle hitchhiking long distances in infested plant material such as unseasoned firewood or green wastes. If it reaches the east coast, the impact on urban trees, bushland and crops could be very serious."
Without human assistance, the beetle could advance up to three kilometres per year, but the movement of infested plant material could transport the PSHB much faster.
Summer is the highest-risk period for new outbreaks in most areas, as warm conditions cause beetle numbers to surge.
Co-author Professor Ben Phillips, also from Curtin's School of Molecular and Life Sciences, said the model was the most detailed ever built for this invasive pest.
"By looking at the beetle's full life cycle and the temperatures it experiences inside trees, we can identify where outbreaks are most likely, and when," Professor Phillips said.
"This gives agencies a powerful tool to plan surveillance, respond to new detections and hopefully limit the establishment and spread."
The PSHB has already had a devastating impact on Perth's urban tree canopy and has triggered a multi-million dollar response effort in Western Australia.
Last year, the National Management Group determined the borer was no longer technically feasible to eradicate and a national Transition to Management plan is now in place, which includes a quarantine area for the Perth metropolitan area.
The study highlights the importance of preventing the beetle from reaching other states.
The model was also applied across California, South Africa, Israel and South America, where the PSHB is already established.
The research team says the modelling system can now be used to forecast future hotspots, guide national biosecurity decisions and test how different control strategies could slow the beetle's spread.
The researchers have also created an online app called the 'PSHB Survey Planner', which lets the user see the best times of year to look for the PSHB, anywhere in Australia.
Early detection is critical for controlling the PSHB, but the resources for continuous surveillance are not always available.
The app is a tool to help make decisions on when monitoring efforts should be prioritised. Conducting surveys when there's the best chance of detecting the PSHB can help stop the beetle in its tracks.
The PSHB Survey Planner is quick and easy to use, and can be found at: https://coates-a.shinyapps.io/Shiny_PSHB/
The work was funded by the WA Government through the WA Premier's Science Fellowship Program, which supports Professor Phillips as a Premier's Science Fellow.
The paper 'Boring Beetles and Super Models: Mapping Potential Distributions of a New Invader' was recently published in the international Journal of Biogeography.
