The Department of Conservation is geared up to mount an intensive strike against a great white butterfly spring breeding surge and is again asking Nelson Tasman residents for help in clearing the pest butterfly from the region and New Zealand.
DOC has set up a dedicated team, numbering up to 25, to carry out concentrated searching of gardens to look for and remove great white butterfly caterpillars and eggs.
The pest butterfly poses a major threat to home and commercial brassica crops and endangered native cresses.
Already this spring, 71 egg clusters have been found and 70 adult butterflies have been killed.
The support of local people is essential to the DOC-led programme to eradicate the great white butterfly in Nelson Tasman.
Householders are asked to look for the butterfly’s caterpillars and eggs in their gardens and report any found to the Ministry for Primary Industries (MPI) hotline 0800 80 99 66. The caterpillars and eggs can be found in clusters on its favoured plants which include nasturtium, honesty and brassica vegetables such as broccoli, cabbage and cauliflower.
The tiny, yellow eggs are found in clusters of 30 to 100. Young caterpillars are also tiny and are yellowish with a shiny black head. The larger caterpillars are speckled greenish-yellow and black with three yellow lines along their bodies and they grow to about 50 mm in length.
DOC is also asking the public to help kill great white butterflies. Female butterflies can lay as many as 750 eggs so killing butterflies helps prevent their numbers increasing and the butterfly spreading to new areas.
People taking trailers, boats and caravans out of the Nelson Tasman region are asked to check no great white butterfly pupae are on board before they leave home. Any pupae found should be reported to the MPI hotline 0800 80 99 66 and removed before leaving to avoid spreading the pest butterfly to new locations.
Large patches of overgrown nasturtium can become butterfly breeding hotspots and these are being cleared where possible. DOC is asking householders to remove or cut back nasturtium. If people don’t want to remove nasturtium plants they are asked to keep checking them for caterpillars and eggs and report any found to the MPI hotline 0800 80 99 66.
Project Manager Bruce Vander Lee said knocking back the pest butterfly’s breeding spikes in spring and autumn was critical to achieving its eradication.
‘We put in an intensive effort against a great white butterfly autumn breeding spurt, searching out and removing infestations, and we are hoping as a result there will be fewer butterflies to set off its spring breeding burst. But that will be determined in how many infestations our field staff find and the public report to us in coming weeks.
‘Many Nelson Tasman residents will be out in their gardens tending to plants over spring. We are asking them to keep watch for great white butterfly caterpillars and eggs.
‘Leaves being rapidly chewed away on plants could be a telltale sign they are being attacked by the mob-feeding caterpillars that can quickly demolish plants.
‘We have had great support from the Nelson Tasman community so far and working together we have a chance of clearing this pest from our region and stopping it becoming a permanent, widespread major pest in New Zealand.’
Garden searches by the eradication team this spring are initially focussed on Nelson city where most infestations occur.
Householders in Richmond and in Tasman should also watch for butterfly infestations as the butterfly can fly to new locations. Infestations were found in Richmond for the first time last summer.
When infestations are found or reported, field staff remove the caterpillars and eggs, mostly by hand. Searches are carried out of neighbouring properties as they could also have infestations. Because the butterfly flies around, repeat visits to properties are needed to check for new infestations.
DOC launched the great white butterfly eradication programme in November last year. Agencies supporting it include MPI, Nelson City Council, Tasman District Council and Vegetables New Zealand.
Eradication team field staff have carried out over 28,000 garden searches since November and 850 butterfly infestations have been found and removed since it was first discovered in a Nelson city garden in 2010.
Over winter, a smaller field team searched for the hibernating pupae and also removed any caterpillars and eggs found that survived the colder conditions.