This highly invasive beetle is about the size of a sesame seed, and attacks a wide range of plant species. Photo: DPIRD.
Biosecurity experts urge people thinking of bringing firewood, untreated wood chips or live woody plants here from Perth to think again.
All of these things have the potential to bring a tiny, unseen menace that kills trees and may be impossible to eradicate.
Weekender contacted Dr Carol Booth, spokesperson for the not-for-profit group The Invasive Species Council, after readers asked us to investigate their concerns about polyphagous shot hole borer beetle coming to Esperance.
“Your concerns are real,” she said.
“You only need one female that could establish a population.
“This beetle bores into trees and shrubs and can live for several months if a branch or tree is cut down, and can also survive in wood chipping if the pieces are large enough.
“If somebody brought a woody shrub down in a pot plant, or firewood, or wood chips, there could be a beetle in it.”
Last month DPIRD chief plant biosecurity officer Dr Vincent Lanoiselet told a Parliamentary committee the currently acceptable method for treating wood to use as garden mulch.
“Infested wood is mulched and chipped to less than a 2.5 centimetre diameter and the chipped mulch is moved to a commercial property for hot composting within the quarantine area to create potting mix according to Australian standards,” he said.
“If those steps are followed, there is a greater-than 99.9 per cent kill rate of polyphagous shot hole borer,” he said.
“I think the biggest risk is the people won’t take any notice of the rules,” Dr Carol Booth said.
“If they are moving house and have brought their woody pot plant or are going camping and bring a bit of firewood that is probably where the biggest risk comes from.”
UWA entomologist Theo Evans said it was “really important” to be cautious.
“If I was in Esperance or anywhere outside of Perth I would not be buying any woody sapling from Perth and transporting it out of Perth,” he said.
“The risk is really tiny but it only has to happen once.”
How the killer works
The polyphagous shot hole borer beetle bores tiny holes into trees and then plants a fungus which it feeds on.
The fungus eventually kills the tree.
Associate Professor Evans said the beetle was still being studied and it tended to change its behaviour from one species of tree to another.
“For avocados they seem to attack the branches so you can prune off the invested branches and the tree survives,” he said.
“But they attack the trunk of a mango so it will kill the mango tree because it has attacked the trunk.
“We have got evidence that they are attacking relatively small saplings, so 2-3cm diameter.”
Prof. Evans said he did not know how many species of smaller saplings had been found to host the beetle.
He said it could only have been spread by humans because it could not fly very far on its own and it did not fly at all if the weather was windy.
“They are so small and so bad at flying that if the wind gets too great they just get blown around,” he said.
“All bark beetles that have been studied fly when it is calm or a in very slight breeze which will waft the smell of a host toward them, and they will therefore fly upwind.
“They are only about 1.5mm long, so 20 to 80 metres is a marathon distance for them.”
Prof. Evans said the beetles only had “a certain amount of fat” to keep then going once they left their home tree.
“They are not going to eat until they find a host tree, bore into a host tree, plant the fungus and wait for the fungus to grow so they can eat it,” he said.
“The further they fly, they have got less energy to survive.”
WA Forestry and Agriculture minister Jackie Jarvis has been contacted for comment.
