A TINY insect could hold the key to tackling flaxleaf fleabane, one of the most invasive and costly weeds in Australian grain production.

Researchers from CSIRO, Australia’s national science agency, are exploring if the stem-boring weevil Lixus caudiger could be used as a biological control agent under a project funded by the Grains Research and Development Corporation.

CSIRO is working closely with collaborators in Brazil and France to identify and test fleabane’s natural enemies.

The weevil, nicknamed “Weevil Knievel”, is native to South America and has shown promising results from early trials.

It feeds on fleabane leaves and stems, while its larvae burrow inside the stem tissue, hollowing out plant structures and weakening them until they collapse. 

The internal feeding often prevents the weed from flowering and setting seed, affecting its ability to spread.

The colony of weevils, housed in CSIRO’s quarantine facilities, is undergoing further testing, with researchers carefully monitoring feeding, mating, egg-laying and larval development across a wide range of test plants. 

If the insect proves safe and effective, CSIRO will prepare submissions for regulatory approval before any potential field release.

The weevil is the focus of CSIRO entomologist Dr Michelle Rafter’s research and is one of several new potential weed biological controls unveiled by Dr Ben Gooden in a keynote presentation on at the South Australian Weeds and Pests Conference in Adelaide recently.

Dr Gooden said the weevil research was part of a broader push to expand weed control options as part of GRDC’s weed management investigations.

“The weevil is just one of four promising fleabane biocontrol candidates, but it’s shaping up as potentially one of the most impactful,” Dr Gooden said.

Dr Rafter said there were promising signs that the weevil was highly specialised to fleabane, while not causing any damage to crops.

“So far, our testing shows the weevil is restricted to fleabane and its close relatives,” she said.

“That’s exactly what we want in a biocontrol agent, something that hones in on the target weed without threatening native plants or crops.”

Dr Rafter said it could be several years before the weevil was released in paddocks.

Flaxleaf fleabane (Erigeron bonariensis) has become a headache for farmers across the northern, southern and western grain growing regions where it flourishes in non-cropped areas such as fence lines and roadsides, sending clouds of wind-borne seed back into cropping paddocks.

GRDC Weeds manager Sarah Morran said investment in biocontrol was a priority because of its potential for cost-effective, long-term weed suppression.

“Weeds cost growers significant amounts of money and impact on crop yields,” she said.

“By investing in innovative approaches like biocontrol, we’re helping growers tackle herbicide resistance, using nature’s own checks and balances to help manage weeds more sustainably.

Ms Morran said weed biocontrol was not designed to eradicate weeds but to reduce their impact and allow other management practices to be more effective.

“Weeds like flaxleaf fleabane won’t be beaten by chemicals alone,” she said.

“Integrated solutions, including biological control, could offer a sustainable pathway to protecting yields and profitability,” she said.