By Trish Grant, Communications Advisor
Zero great white butterfly detections for more than 14 months indicates the DOC-led programme to eradicate the pest in Nelson Tasman has been successful but further searching over autumn will help confirm this.
Since the great white butterfly eradication programme was launched in November 2012, concerted searching of gardens and public reports resulted in 2,696 butterfly, caterpillar, egg and pupae infestations being found.
The last detection was on 16 December 2014 when a male butterfly was caught.
The eradication team had carried out more than 90,000 property searches since the last butterfly find and it was encouraging that these had not turned up any further infestations.
DOC’s advisors have told me that more searching and time is needed to establish if the great white butterfly population has been eradicated. If we continue to have no butterfly detections over the next four months, we will then consult with our experts to assess what the likelihood is of eradication success.
There has been a fantastic team of committed DOC rangers doing a great job in hunting out the great white butterfly. The tremendous support of the Nelson Tasman community has also been essential to knocking down the butterfly population.
DOC is grateful for the support of other agencies including Vegetables New Zealand who have contributed funding. The Ministry for Primary Industries has also funded research to assist the eradication programme and allowed use of its Exotic Pest and Diseases hotline for public reporting of butterfly finds.
Introduced wasps Cotesia glomerata and Pteromalus puparum that parasitize white butterfly caterpillars have also played a significant role in suppressing the butterfly population.
The great white butterfly poses a major threat to native cresses and to commercial and home brassica crops, including sheep and dairy forage crops. Its caterpillars voraciously feed in mobs, rapidly skeletonising host plants.
An assessment by an independent economist found that if the butterfly became widespread in New Zealand it could cost the country $14.5 million a year. The costs would be incurred in spraying home and commercial crops to protect them from butterfly damage and in protection measures for threatened native cresses.
The great white butterfly was first discovered in a Nelson garden in 2010. It spread in the city and into Tasman but has been contained in the region. If it is not stopped it could spread to others parts of New Zealand.