Commando strike on doublegee by Roger Nicoll


ARMED with an Israeli weevil that effectively attacks the crown of doublegee, CSIRO scientists are engaging in long-term biological warfare against this and related species of Emex.

As part of the current research into the bio-control of doublegee (Emex australias) and lesser jack weeds, CSIRO Entomology scientists are rearing, releasing and monitoring the impact of the red apion weevil, Apion miniatum.

This bio-control research project aims to greatly reduce the incidence of these weeds and thus their impact on grain production.

To date, the research team has released more than 40,000 red apion at approximately 50 sites across the wheatbelt in south-west Western Australia and has supplied starter colonies to research collaborators in NSW and South Australia.

Research project leader, Tim Woodburn of CSIRO Entomology, says scientists have successfully finetuned the mass rearing of red apion in tunnel houses at Floreat, WA, and have made good progress in techniques to successfully oversummer the insects.

"Results from our field cage experiments and our experimental releases of red apion have also been very encouraging," Mr Woodburn says. "The insect effectively attacked doublegee plants at the vast majority of release sites during the first growing season after release.

"All indications are that the insect is establishing well, but we won't really know for three to five years because red apion produce only one generation per year and are slow to build up. At the moment it is hard to gauge progress because finding one insect amongst 10 square metres of plants is like finding the proverbial needle in the haystack."

Slow build-up of a bio-control agent is not uncommon. The 12-year-Iong build-up for the Paterson's Curse crown and root weevils is a good example.

Experimental evidence supports the research team's optimism that red apion can successfully survive the hot and dry West Australian summers. Experiments show that red apion can keep going in the Australian heat without food or water for five months.

"We estimate that 60,000 insects successfully oversummered at our Cunderdin release site alone, although no establishment figures are confirmed at this stage."

Doublegee, or three-cornered jack, has long been a thorn in the side of southern Australian grain growers and continues to cost producers $40 million each year in Western Australia alone. Annual per capita herbicide cost to WA growers, to control doublegee and wild radish, can be as high as $76,000.

"The beauty of bio-control is that it is a target-specific and sustainable method of weed control," Mr Woodburn says. "Biocontrol promotes organic production which is increasingly sought after by the community and is attracting premium prices.

"Over the long term we hope biocontrol will reduce the soil seedbanks and the amount of doublegee that can grow during the pasture phase of crop rotation.

The ultimate aim is to reduce doublegee infestation to a level that has minimal economic impact on farmers."

Program 3.3.3 Contact: Mr Tim Woodburn 0893336647