Prickly acacia weapon approved in 'world first'

In what could be a major win for farmers, the federal Department of Agriculture, Water and the Environment 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, the adult thrips induce rosette galls on shoot tips and buds.

As the gall development progresses, deformation occurs, resulting in shoot-tip dieback, stunted plant growth in juvenile plants and no flowering or fruiting in mature plants.

A total of six insects have been released as biological agents for the control of prickly acacia, and while two agents have become established, the impact of one is relatively small while the other has established only at coastal sites.

Prickly acacia is a Weed of National Significance that infests over seven million hectares of the Mitchell grass downs in western Queensland, as well as scattered infestations in coastal Queensland, NT, SA and WA.

It also costs primary producers $9 million a year by decreasing pasture production and forming impenetrable thickets that hinder the mustering of livestock and restrict their access to watercourses.

Flinders Shire Council Mayor Jane McNamara said prickly acacia was widespread in the Flinders Shire and along the Flinders River 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 which was introduced into Australia as a fodder plant by the government ...," Ms McNamara said.

A Climate Change, Energy, Environment and Water spokesperson said after considering the information available, federal Environment Minister Tanya Plibersek decided to include gall-inducing thrips in the list of specimens taken to be suitable for live import under national environment law.

They said the addition to the live import list would help the Queensland government in continuing its research and biological control of prickly acacia in Western Queensland.

In its native range, the gall-inducing thrips occurs widely in regions of Ethiopia, so surveys were conducted there at several sites from 2014 to 2017 and 1600 insects were imported in 2015 and 2016 into a quarantine facility at the Ecosciences Precinct in Brisbane.

Adults can now be transferred into cages with prickly acacia in a non-quarantine glasshouse for mass rearing.

Stem galling thrips with adults and larvae established on prickly acacia in the non quarantine glasshouse will be transferred to the Tropical Weeds Research Centre in Charters Towers for mass-rearing and field release.

Mature galls from infested plants will be collected and field released in prickly acacia infestations in north and central Queensland in partnership with Prickly Acacia Alliance Forum and other NRM groups.

After releases in Queensland, additional releases will be made in the NT and WA.

Prickly acacia first spread widely in Australia in the early 1900s when it was planted as a shade and ornamental tree in the Bowen and Rockhampton districts.

In 1926, the Queensland Department of Agriculture recommended planting it for shade and fodder for sheep in western Queensland, however, the introduction of cattle into the area and good wet seasons in the 1950s and 1970s contributed to an explosion of the weed.

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