The Sydney golden wattle (Acacia longifolia), native to south-eastern Australia, was introduced to New Zealand for ornamental planting and dune stabilisation.
However, this fast-spreading species poses a serious threat to our fragile dune and wetland ecosystems, particularly in disturbed and coastal areas. Each tree produces vast quantities of seeds that can remain viable for decades, allowing it to rapidly invade new environments.
It has invaded coastal areas of Tasman, particularly the Moturoa/Rabbit Island sand dunes, where it thrives right down to the high tide mark. It is highly adaptable, growing in various soil types and tolerating salt exposure.
In December 2024, Manaaki Whenua Landcare Research supplied us with 150 gall-forming wasps, which were released at Moturoa/Rabbit Island to help control the spread of Sydney golden wattle. Over time, these wasps are expected to spread to other infested areas, hopefully providing a long-term, sustainable control solution.
South Africa has also struggled with Sydney golden wattle invasions, and has implemented a successful biocontrol programme. Their initiative, launched in the early 1980s, introduced two natural enemies from Australia: a seed-feeding weevil and a gall-forming wasp (Trichilogaster acaciaelongifoliae). These biocontrol agents have significantly reduced seed production by more than 90 percent.
Extensive research before the wasp’s release in New Zealand confirmed its high host specificity, meaning it poses no risk to native plants. Additionally, the wasps are harmless to humans. These tiny wasps (3 – 4 mm in size) lay their eggs inside the plant’s flower and vegetative buds, causing large growths (galls) to form instead of flowers and new shoots. This process suppresses seed production which reduces spread.
Sydney golden wattle gall-forming wasp:
Large galls formed by wasps:
