Beetle army wages war on pest weed

An army of 400 small beetles will be deployed to combat a big pest weed problem that's taken root in New Zealand's oldest arboretum.

The beetles have been specially bred by Landcare Research to tackle tradescantia – also known as wandering willie – in the William Hall Arboretum and Walk which is located in Thames.


Waikato Regional Council's Whitianga-based pest plant officer Benson Lockhart releasing small beetles to help tackle the tradescantia problem at Thames' William Hall Arboretum and Walk. Photo: WRC

Their release is being carried out by the Waikato Regional Council in partnership with the Thames-Coromandel District Council and Forest & Bird.

For the past two days WRC's Whitianga-based pest plant officer Benson Lockhart has been releasing the beetles with the help of TCDC and Forest & Bird staff, plus community volunteers.

'We've released three different types of beetle, with each one attacking different parts of the plant – the leaf, stem and tip,” explains Benson.

'These beetles have got a big job ahead of them, because tradescantia is thick throughout the arboretum.”

Landcare Research supplied 200 tradescantia tip beetles and 100 tradescantia stem beetles, while Benson harvested the 100 leaf beetles from a Hahei site where they've been deployed to combat the tradescantia problem for several years.

At Hahei, where the beetles are well established and working together, tradescantia is noticeably diminished and allowing native karaka seedlings to come back through.

'The beetles have had time to get established at Hahei and it's awesome to see some good results starting to show. We're hoping to see the same here at the arboretum.”


Tradescantia fluminensis, also known as ‘wandering willie'. Photo: www.weedbusters.org.nz

Tradescantia smothers the ground, preventing native tree regeneration. The plant is also a real nuisance for home gardeners, as well as causing allergic responses in dogs.

The pest plant is so widespread in New Zealand that manual or chemical control on a large scale is simply not feasible.

'That's where biological control – or biocontrol – comes in. It uses a living organism to control another, and it's a method that has been used very successfully across New Zealand since the 1920s to safely control a number of different weeds.”

These biocontrol agents take time to establish, explains Benson. But it's expected the tradescantia beetles will support pest plant control work already being carried out by TCDC, Forest & Bird and community groups in the arboretum.

Landcare Research undertake rigorous testing to ensure biocontrol agents are host specific in New Zealand conditions. The tradescantia beetles have been approved since 2011.


The beetle army consists of 200 tradescantia tip beetles, 100 tradescantia stem beetles, and 100 leaf beetles harvested from a Hahei site where they've been successfully deployed for several years. Photo: WRC

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