Weevils with a big job to do

Two hundred tiny weevils on a big mission are being released in Southland this week.

The Darwin's barberry seed weevils are being released as part of a biocontrol trial aimed at reducing the spread of Darwin's barberry, a pest plant with the potential to overrun native plants and farmland.

Southland played host to the world's first biocontrol release of the weevils last year, and they have now also been released in the Wellington and Manawatu regions.

Environment Southland senior biosecurity officer Randall Milne says the Chilean weevils have been bred in a containment facility in Lincoln by Landcare Research and will be released in a valley on Bushy Park Road, near Waimumu. The release site has been selected as it has areas of regenerating shrubland with Darwin's barberry that the landowner is willing to leave as a trial site. This provides a suitable situation for the weevils to establish and Environment Southland can then follow their progress over time.

Randall says the use of the weevils as a biocontrol agent is still very much in a trial phase.

It is still unknown how they establish themselves in the field and what level of impact they will have, but they are a natural pest of Darwin's barberry in Chile.

The adult weevils feed on the new growth, but it is the larvae which will have the biggest impact by feeding on the seeds. If successful, the weevils will help reduce the spread of Darwin's barberry.

Extensive tests were carried out on the Darwin's barberry seed weevil to ensure it does not damage any other plant species.

A further release of 200 more weevils will also be carried out at another location in Southland if the weevils have had a good breeding season.