The public is being called on to help eradicate a notorious pest, the great white butterfly, before it spreads further.
The Department of Conservation is leading a multi-agency approach to stop the butterfly from invading the country and causing millions of dollars of damage to plant life and crops.
The caterpillars are speckled black and greyish-green, with yellow lines along their bodies, and can be identified by feeding in groups on plants - favouring brassica vegetables, particularly cabbages and broccoli.
Surveillance units have already been formed and are scanning Nelson for caterpillars, catching them before they turn into butterflies.
Tasman-based Vegetables New Zealand director Mark O'Connor said crops worth about $80 million a year were at risk of being damaged and wiped out by the pest which also ate oil-seed rape.
New Zealand insect ecologist Richard Toft is leading a team from Entecol to carry out the eradication programme under a contract to DOC. The operation is also in conjunction with the Ministry of Primary Industries, Tasman District Council and Nelson City Council.
DOC Motueka area manager Martin Rodd urged residents to look for the butterfly's caterpillars and eggs and report suspected findings.
He also wanted to hear from residents in Richmond and Tasman to find out if the pest had spread beyond the city.
It was thought the butterfly had so far been kept within a 6-kilometre radius of Port Nelson, but surveillance units were also searching outside that area. After locating the pest they were physically removing the caterpillars and eggs and, when necessary, applying an organic insecticide to host plants, Mr Rodd said.
The first great white butterfly was found in Nelson in 2010 and there have been 275 confirmed species.
"In attempting to eradicate the great white butterfly from Nelson, we are attempting to eradicate it from New Zealand and stop it becoming established as a major pest in this country.
"The species can fly long distances - sometimes hundreds of kilometres - so would eventually spread throughout New Zealand if left unchecked," Mr Rodd said.
To report sightings of any caterpillars and eggs call the Ministry of Primary Industries hotline, ph 0800 809 966.
- © Fairfax NZ News
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