Scientists have discovered a new biocontrol measure to fight a destructive wasp that attacks the softwood pine trees we rely on to build our homes and furniture.
Key points:
- The Sirex wasp decimated pine plantations when it reached Australia
- Biological controls have helped keep the wasp’s damage in check
- A new nematode could be bred and released in the battle against the wasp
The Sirex wood wasp drills through the bark of pine trees to deliver a double whammy — injecting its venom as well as a fatal wood-rotting fungus that pre-digests the wood for its larvae.
The invasive insect almost destroyed Tasmania’s radiata pine industry when it arrived in Australia in the 1950s, and killed millions of trees in the late 1980s on the South Australia-Victoria border.
Biological controls have been crucial to limiting its damage to Australia’s plantation softwood industry, valued at $1.22 billion in 2020–21.
Former CSIRO scientist Robin Bedding pioneered mass-rearing a nematode to control the wasp after discovering a roundworm with a double life cycle, capable of both sterilising Sirex females and feeding on the fungus spread by the wasp.
It has kept the wasp and its damage in check, but there have been challenges in breeding it.
New biocontrol option
Now, a Queensland scientist has helped identify a new weapon in the war against the invasive wasp.
Researchers discovered a nematode called Deladenus siricidicola (Lineage D) in forests in New South Wales, South Australia, Tasmania, Victoria and on New Zealand’s North Island.
Helen Nahrung from UniSC’s Forest Research Institute shares credit for the discovery with the NSW Department of Primary Industries, the University of Pretoria and Scion, the New Zealand Forest Research Institute.
It is considered both “exciting and significant” for adding much-needed genetic diversity to the timber industry’s biocontrol options.
“It has two very distinct forms — one which feeds on the Sirex fungus, and then when it’s in proximity to Sirex larvae, it converts into a parasitic form and burrows into the larvae, reproduces and invades the reproductive organs of the developing females,” Dr Nahrung said.
“And then when the wasp emerges, instead of laying eggs into the next tree, it lays this packet of nematodes and then they go on to sterilise the next generation of females.
“It’s amazing. It’s such a complicated system, it’s really crazy.”
Dr Nahrung said the new roundworm posed no threat to the environment because it only attacked wood wasps.
“It’s a very safe system; I know with biocontrol, people freak out because of all the mistakes made from the past with the cane toad, but no, this is very safe.”
She explained how the nematodes were released in pine plantations.
“They use a trap tree plot program where they stress trees using herbicides so they’re attractive to the wasps, and the wasps then concentrate on that trap tree plot.
“Then the tree is felled with the wasp larvae in it and then the nematodes are inoculated into it with a specially designed hammer and punch and they parasitise the Sirex larvae.”
The Sirex wasp has not been detected in Western Australia or the Northern Territory but has arrived in Queensland, where it is yet to reach the crucial coastal plantation regions of Beerburrum north of Brisbane and the Fraser Coast.
Timber Queensland chief executive Mick Stephens said the industry remained vigilant against the threat of the pest taking hold in the state.
“This biotechnology is an important defence against the Sirex wasp and helps to protect our valuable forest products and timber industry in Queensland,” he said.
Dr Nahrung said researchers had been collecting samples of the new nematode from pine plantations for mass-rearing it for release against the Sirex wasp.
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