Non-stinging wasp creates positive buzz as control tool against invasive pest plant in Horizons region

Horizons and Manaaki Whenua staff members inspecting galls on a Sydney golden wattle plant. Photo / Supplied

A non-stinging wasp introduced by Horizons Regional Council is showing promising signs of being a viable control tool against a pest plant along the region’s coasts.

Horizons was granted permission by the Environmental Protection Authority to introduce the bud-galling wasp Trichilogaster acaciaelongifoliae in late 2022 as a potential way to control the highly invasive plant Sydney golden wattle. The wasp has previously been deployed successfully against the wattle in South Africa and Portugal.

The plant was introduced to Aotearoa as an ornamental plant in the 1800s but now dominates vast swaths of habitat along the west coast from Whanganui to Waikawa.

Horizons environmental manager Craig Davey said the plant had a significant impact on the environment.

“It suffocates other native species, preventing their growth and creating a monoculture of Sydney golden wattle.

“People are likely familiar with the plant, especially in places like Himatangi Beach where the infestation covers most of the dunes, although they may not realise it is a pest.”

The plant is also an invader of wetlands and a known cause of hay fever.

Davey said a recent inspection found the wasps had created galls on the plants along the western coastline.

“This was a really exciting discovery because it was the first opportunity for our pest plant team to determine if the release of this friendly, non-stinging wasp has been successful; finding galls means it has.”

The wasp lays its eggs on an area of the plant that will become flower buds. The plant then produces growths, known as galls, which prevent flowering and seed production.

“No flowers, no seed, no spread of Sydney golden wattle,” Davey said.

The wasp spends almost all of its life feeding on the galls inside the plant, spending only about three days outside the plant to find a mate and, if female, lay eggs before dying.

It lives purely to attach itself to Sydney golden wattle, meaning it will not impact native plants and has no bite or sting.

Davey said coastal communities in places like Whanganui were the motivating factor behind securing permission to release the wasp.

“These communities have experienced first-hand the devastating impact on dunes.”

He thanked staff from Manaaki Whenua Landcare Research for their assistance throughout the many years of the project and with inspecting the sites of the wasp’s release.