Gall flies released on Croker Island
In early December 2025, the NT Government’s Weed Management Branch (WMB) released gall flies (Cecidochares connexa) on Croker Island as part of collaborative research with the Queensland Department of Primary Industries.
This biocontrol agent targets siam weed (Chromolaena odorata) an invasive plant that threatens biodiversity, livestock, and human health. The release marks a bold step in long‑term weed management.
For more information about the siam weed, go to the Northern Territory Government website.
Led by WMB’s Joshua Maeer and Gerald Danao, the team worked with Garngi Rangers Ashley and Mike and Northern Land Council Ranger Coordinator, Stuart Hicks. Together, they combined monitoring with the release. Despite damage from Cyclone Fina, transects remained intact and quadrat sampling was partially completed. Genetic sampling was also undertaken to trace where the siam weed on the island originated.
The highlight was the mass release: an estimated 1,200 gall flies were introduced, including 50 adults already emerging at the site. By laying eggs inside siam weed stems, gall flies create galls that stunt growth and reduce reproduction. If established, they could weaken siam weed’s dominance and allow native ecosystems to recover. Quarterly monitoring and further releases are planned to strengthen populations.
This first mass release on Croker Island marks a turning point in the Territory’s fight against siam weed, a hopeful sign that persistence, science, and collaboration can restore ecological balance.
Do not attempt to control siam weed by yourself. If you have seen siam weed, contact the WMB by calling 08 8999 4567 or emailing weedinfo@nt.gov.au.
