23 Mar 2015

Beetle introduced to tackle weed

2:47 pm on 23 March 2015

In a world first, a Chilean beetle is being introduced in New Zealand as a biocontrol agent to tackle a weed that scientists say could become as big a problem as gorse.

Lindsay Smith

Lindsay Smith Photo: SUPPLED

The weed, Darwin's barberry, is an orange-flowered thorny shrub that originated in Chile.

It has been spreading rapidly across the country, particularly in Southland, and is threatening to overrun native plants and farmland.

Landcare Research scientist Lindsay Smith has been working closely with Chilean scientists for a number of years and said New Zealand would be the first place in the world to use the species - barberry seed weevils - as control agents.

Barberry seed weevil

Barberry seed weevil Photo: SUPPLED

He said at the start of biocontrol programmes, scientists returned to the pest plant's country of origin to try and find control agents that could be used.

"In this case it was South America, Chile, so we surveyed the barberry plants in Chile looking for damaging insects and potential agents," he said.

"In our surveys, we came across two weevils that looked very promising - the seed-feeding weevil and a flowerbud-feeding weevil - and certainly looking at the reduction in seed in Chile by this seed feeder, we thought this would certainly be a great agent to introduce here."

Mr Smith said 70 barberry seed weevils had been released just north of Invercargill and several thousand more were planned to be released early next year.

"Both the adult and the larvae feed on Darwin's barberry. The adult feeds on the new growth of the plant but it's actually the larvae that do the damage," he said.

"They burrow into the berry, feeding on the seeds within the berry, therefore reducing the amount of seed being dispersed by birds."

Mr Smith said extensive tests were carried out on both the adult weevils and their larvae to ensure they can't damage any other plant species.

Get the RNZ app

for ad-free news and current affairs