Fly Release to Weed out Biosecurity Threats in the Cassowary Coast

The Cassowary Coast is flying in to weed out a noxious plant species thanks to hungry fly larvae with a taste for Siam weed (Chromolaena odorata).

Council’s Natural Environment and Sustainability team culminated a four-year project of mass-rearing and releasing of a biological control fly called the Siam gall fly (Cecidochares connexa) at infested sites including Fishers Creek Road, Stoters Hill and Mena Creek Road.

Cassowary Coast Councillor for Development, Planning and Environment Jeff Baines explained how the flies are bred by Biosecurity Queensland (BQ) for their insatiable appetite for Siam weed.

“The flies are reared by BQ in Charters Towers as an important weapon in the battle to control this weed which is widely considered to be the world’s worst,” Councillor Baines said.

“The female Siam fly deposits its eggs into the stems of the plant and when the larvae feed on the plant material inside the stem it causes a gall to form.

“Over the next sixty-five days the galls restrict the plant’s ability to flower and produce seed resulting in stunted regrowth with less seed and lower viability.”

Councillor Baines congratulated Council’s Natural Environment and Sustainability team on a job well done as they observed galls from previous releases were still taking effect.

“It’s good to see evidence that the program is working across these key release sites, in particular at Stoters Hill where the fly has established and is spreading in the area.

The collective effort between Council and the Queensland Department of Agriculture and Fisheries, Department of Environment, Science and Innovation and HQ Plantations as well as landholders, has seen over 14,500 flies and 2,540 galled-stems released at 67 sites within Cassowary Coast Regional Council over the last four years.

With the flies having established and spread, in the years to come it’s intended that they’ll spread further to help control and manage this serious weed in northern Queensland.

Image Caption: Councillor Baines at Stoters Hill with the Siam Weed