Prickly acacia weapon approved in 'world first'

In what could be a major win for farmers, the federal government recently approved a proposal by the Queensland Department of Agriculture and Fisheries to release the sucking insect, gall-inducing thrips (Acaciothrips ebneri), for the control of the weed.

According to DAF, this is the first time a rosette-gall inducing thrips has been evaluated as a weed biological control agent for any weed around the world.

Native to northern Africa, thrips induce rosette galls on shoot tips and buds, resulting in shoot-tip dieback, stunted plant growth in young plants and no flowering in mature plants.

Six insects have been released for the control of prickly acacia but their impact has been relatively small or isolated.

Prickly acacia infests over seven million hectares of the Mitchell grass downs in western Queensland and costs primary producers $9 million a year by decreasing pasture production and forming impenetrable thickets that hinder mustering and restrict watercourses.

A Biosecurity Queensland spokesperson said the thrips has now been removed from quarantine in Brisbane to a glasshouse for mass rearing and field releases.

"Research has shown that the gall thrips are highly host specific and have the potential to cause serious damage to prickly acacia shoot tips," they said. They said testing confirmed the gall thrip didn't pose a risk to any non-target plants.

Flinders Shire Council Mayor Jane McNamara said prickly acacia was widespread in the shire and there had long been the desire for biological control for the weed.

"Many years of research have gone into such controls and we welcome another weapon to fight the widespread infestations of prickly acacia," Ms McNamara said.

Southern Gulf NRM CEO Geoff Penton has also welcomed the news but warns it is too early to see the thrips as the ultimate cure.

"It's possible that some landholders will see the news of the new control and go, 'okay, we can down tools'," Mr Penton said.

"We've seen that before with other biological control releases and then it doesn't live up to people's expectations. We just need to understand what impact it will have before people decide to stop doing their current control strategy."

The NRM is looking to run 12 to 18 months of field trials across about 20 sites to understand what impact the Ethiopia-derived insect is going to have.

"We don't know how it will perform in the wild. We've got a lot of native insects, so it could get predated and not generate enough numbers to have a big impact," Mr Penton said.

"Because it's so tiny, it might move on the wind and be fantastic, but if it can't move to neighbouring plants, that might become very labour intensive to move.

"It might be really good for dense infestations, but no good for scattered infestations. It might be really good on small plants, but doesn't have a big enough impact on big plants. It might be really good in dry climates but not in humid."

Gall thrips occurs widely in regions of Ethiopia, so surveys were conducted and 1600 insects were imported in 2015-16 into the Ecosciences Precinct in Brisbane.

Prickly acacia first spread widely in the early 1900s, and in 1926, the Queensland government recommended planting it for shade and fodder.

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