USC scientist tackles rogue ladybirds and tree-killing wasps

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USC scientist tackles rogue ladybirds and tree-killing wasps


Helen Nahrung takes a core sample from pine tree in Beerburrum

19 October 2014

USC researcher Dr Helen Nahrung just loves creepy crawlies. Whether they are in their natural habitat or under a microscope, she spends her days studying insects of all shapes and sizes.

With over 220,000 insect species in Australia, it’s no surprise that some insects are considered good while others are bad. But, as an entomologist, Dr Nahrung knows the line is not that clear cut.

“Now everyone loves ladybirds,” she said. “They eat pests in backyard gardens, agriculture and forestry – but even they can be a serious nuisance pest in some situations.”

Dr Nahrung carried out research in Tasmania where two ladybird species were causing major problems by forming huge aggregations and hibernating inside commercial buildings during winter.

“Nobody wants to kill ladybirds because they’re the good guys,” she said. “So the company kept trying to move them – gently brushing them off the walls and sweeping them into bins and taking them away – but they kept coming back to exactly the same spot.”

Dr Nahrung and colleagues from the University of Tasmania, supported through funding from the USC Research Futures Collaborative Research Networks (CRN) program, discovered the ladybirds were leaving a chemical trail in the buildings that was irresistible to other ladybirds.

Ladybirds aren’t considered a pest here on the Sunshine Coast, but there’s another critter she’s studying that we really don’t want to meet.

First found in Tasmania in 1952, the sirex woodwasp has slowly crept north, finally crossing the Queensland border into the pine forests of the cooler temperate Stanthorpe region in 2009.

According to Dr Nahrung it is a major problem in plantation pine forests around the world.

“It is an amazing creature that has a symbiotic relationship with a fungus, so they can’t live without each other,” she said.

“When the sirex lays eggs in the pine tree, it also lays fungus spores and some poisonous mucous. The mucous dries out the tree so the fungus can grow and the wasp larvae can eat the fungus. All of that together actually kills pine trees, which is quite incredible.”

Treatment for the sirex woodwasps involves inoculating some trees with nematodes (a type of worm) which invades the sirex larvae and migrates into their ovaries. When those female sirex mature they lay nematode larvae into other trees.

Dr Nahrung and her collaborator at the Department of Agriculture, Fisheries and Forestry, Dr Manon Griffiths, are trying to work out whether this existing treatment will work on the hybrid pine trees grown on the Sunshine Coast and further north.

Dr Nahrung has just returned from the US where she presented her sirex woodwasp research at the International Union of Forest Research Organisations World Congress in Salt Lake City, Utah.

Dr Nahrung is a CRN Research Fellow working with both the GeneCology and Forest Industry Research Centres at USC.

— Jane Cameron

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