A group of high school students is waging biological warfare against an invasive weed threatening Northland's native bush.

The Tradescantia Terminators are a Year 9-10 community problem-solving group at Kerikeri High School who have made it their mission to rid a newly opened walkway of Tradescantia — also known as wandering jew or wandering willy — to stop the mat-like weed smothering native seedlings.

Charlie Potter, 14, said many of the group's nine members lived near the Wairoa Stream track which links the Stone Store, Wairere Falls and Cobham Rd.

The tiny, gold-coloured beetles are fussy eaters, feeding only on Tradescantia leaves. Photo / Peter de Graaf
The tiny, gold-coloured beetles are fussy eaters, feeding only on Tradescantia leaves. Photo / Peter de Graaf

When walking the track the students noticed "heaps" of Tradescantia and realised it would make an ideal challenge for their community problem-solving team.

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First they had to find the best way to get rid of the weed.

"We thought of spraying but the problem is the Tradescantia is so close to the river. Plus we'd need a permit, which is expensive. Then we thought of weeding but there's so much of it and it grows so quickly."

Ngati Rehia kaumatua Alan Munro speaks about protecting the children of Tane Mahuta. Photo / Peter de Graaf
Ngati Rehia kaumatua Alan Munro speaks about protecting the children of Tane Mahuta. Photo / Peter de Graaf

Another option was to try biological control. The students found beetles had been used in other places around the world where Tradescantia was a problem, so they sought advice from Northland Regional Council insect expert Jenny Dymock.

A little beetle called Neolema ogloblini, which eats only Tradescantia, was introduced to New Zealand from Brazil in 2011, and to Northland a few years ago.

Fellow team member Jeany Kim, 14, said the group knew the beetles could be found on King St in central Kerikeri so they made a contraption called a "pooter" to suck the beetles up.

Tradescantia Terminators, from left, Jessica Mooney, Emilia Finer, Wilson Hookway, Michael Mitchell, Emilie Jones, Charlie Potter, Jeany Kim, Charlotte Gamble and Faith Hohepa.
Tradescantia Terminators, from left, Jessica Mooney, Emilia Finer, Wilson Hookway, Michael Mitchell, Emilie Jones, Charlie Potter, Jeany Kim, Charlotte Gamble and Faith Hohepa.

On Thursday, after a blessing by Ngati Rehia kaumatua Alan Munro — who said he hoped it would be for the betterment of Tane Mahuta's children — the students released the beetles in a thick patch of Tradescantia next to Wairoa Stream.

Jeany said research had found the beetles ate only Tradescantia so they posed little risk to native plants.

Emilia Finer, 13, said the problem with Tradescantia was that it smothered and shaded out native seedlings so they couldn't grow and the forest couldn't regenerate.

Faith Hohepa, 14, said the group also wanted to make people aware that even the "littlest bit" of Tradescantia dropped on the ground could grow into new plants and form a dense mat.

Kerikeri High School kapa haka group Te Pou o Manako sings a waiata before the release. Photo / Peter de Graaf
Kerikeri High School kapa haka group Te Pou o Manako sings a waiata before the release. Photo / Peter de Graaf

"It's cool to be able to contribute to the community and make a change," she said.

The students plan to come back regularly to monitor the beetles' progress.

The beetles released on Thursday are informally known as "shinies", due to their iridescence. The adults feed on the edges of the leaves while the larvae strip the centre. The students also hope to release beetles nicknamed "knobblies" which attack Tradescantia's stems.

The Terminators were accompanied by the school's kapa haka group, who sang waiata, and members of the Friends of Wairoa Stream, a volunteer group which built and maintains the track.

Friends member Rob Muir said it was great to see young people taking an interest in the environment. He hoped their commitment to the track would continue.

Jeany Kim releases the beetles into their new home while teammates, from left, Emilie Jones, Charlie Potter, Faith Hohepa and Charlotte Gamble look on. Photo / Peter de Graaf
Jeany Kim releases the beetles into their new home while teammates, from left, Emilie Jones, Charlie Potter, Faith Hohepa and Charlotte Gamble look on. Photo / Peter de Graaf