Shothole borer beetle: US expert Shannon Lynch says Australia has perfect climate for destruction by pest

A highly regarded US expert on a tiny beetle killing Perth trees says Australia still has a window of opportunity to get on top of the invasive pest before it leads to the destruction recorded in California.

University of California Davis forest pathology assistant professor Dr Shannon Lynch said she was envious of Australia’s $41 million war chest and confident Western Australia had the capability to manage the polyphagous shot-hole borer outbreak.

“It’s a lot. I’m jealous. I’m really impressed with just the dedication to biosecurity that Western Australia has,” she said.

“It seems like Australia is really on top of eradication efforts and has those mechanisms in place.”

While the first shot hole borer recorded in the US was found in a Californian trap in 2003, it largely went unnoticed until 2012 when Dr Lynch’s and her colleague Akif Eskalen found an infested backyard avocado tree.

Since then, she’s been at the forefront of the Californian response.

Speaking at a public lecture at Murdoch University on Tuesday evening, Dr Lynch revealed the results of a targeted management operation at Californian’s Disneyland which has about 16,000 trees.

Across a three-year period from 2017-2019, her team recorded dramatically reduced beetle numbers collected on monitoring traps through consistent management activities.

“The beetle population severely, dramatically dropped because of the management practices we were doing in the park,” she said.

“I think with good management and sanitation practices applied with monitoring, it’s possible to reduce the population of the beetle.”

Dr Lynch said she was surprised but not shocked to when she was told the Southeast Asian borer was first detected in Australia in August 2021 near Fremantle.

She said the State’s climate it would be an ideal location for the borer to thrive.

“I was not shocked because it’s another Mediterranean climate like Israel, South Africa, and California. These are all places that look like each other in that sense,” she said.

The entire Perth metropolitan is under a quarantine zone, with trees in at least 26 local governments infested and more than 3000 trees destroyed because of it.

Globally, it has threatened urban tree canopies, forests, and avocado production.

Dr Lynch highlighted that not all trees would be killed after a borer attack, with some just showing dieback before recovering and growing over the borer holes.

The borer also doesn’t target the truck of some species, such as avocado trees, with the branches preferred instead, making infections easier to manage.

Dr Lynch also used the Murdoch talk to address myths and provide tips from her decade of dealing with the pest.

It included removing the complete stump where borers can survive and to not hang traps in branches as they will act like a bait to the tree rather than draw borers out of the truck.

Dr Lynch highlighted a gap in Australian research which could explain key differences in WA’s spread, saying the beetle’s co-existing fungus was different in WA than other global discovers.

The fungus can only survive when transported by the borer, which in turn uses it as a food source and to lay larvae — making them mutually beneficial destructive duo.

In Israel, California, and South Africa the borer carries a fungus known as A-2, however, in WA a new A-18 strain has been found.

“We originally thought that there was a one-to-one relationship between the beetle species and fungus species that it carries,” Dr Lynch said.

“We now understand — through some research and obviously through what the beetle carries in Western Australia — that this relationship with this ambrosia fusarium group is not exclusive.”

The visiting academic said without further studies, how the different strain might impacted the rate of spread and treatment options in WA was unknown.

“We just don’t know. Maybe it’s the infectivity that might be different between this particular Australian fungus from the one that we have in California. There’s just not any research that’s being done into that yet,” Dr Lynch said.

A federal Department of Agriculture spokeswoman said research into alternative trapping, treatment and pruning was being undertaken at a State level.

“The Australian government and all state and territory governments are contributing to the cost of the eradication. Funding is for emergency response, it is not for funding research and development programs,” she said.

A Department of Primary Industries and Regional Development spokeswoman said the agency had engaged with international experts, such as Dr Lynch, since late 2021.

“The US has been battling PSHB for more than 20 years and South Africa for about seven years. Both countries have undertaken significant research,” she said.

Dr Lynch travelled to Israel in 2013 to assess the spread there and South Africa in October last year.

She’s expected to travel to Hyde Park, Kings Park and other locations during her visit to examine the spread in WA through collaborations with Murdoch University, DPIRD and DBCA.