Why it's a pest
The great white butterfly (Pieris brassicae) is a significant pest of brassica crops in numerous countries across Europe and western Asia. In some countries, it is called the large white butterfly.
Its caterpillars feed voraciously in groups, rapidly reducing host plants to a skeleton.
The butterfly can fly long distances – sometimes hundreds of kilometres – so can become widespread.
The great white butterfly was first found in a Nelson garden in 2010. It is thought to have arrived as pupae on goods shipped into the city’s port.
DOC launched a programme to eradicate the butterfly in 2012 out of concern at the threat it posed to endangered native cresses. New Zealand has around 79 native cress species, especially the 57 at risk of extinction.
The great white butterfly also posed a threat to commercial brassica vegetable crops and to farm brassica crops grown to feed dairy herds and sheep.
Other agencies worked with DOC on the eradication programme including the MPI, Horticulture New Zealand, AgResearch and Plant and Food Research.
DOC rangers carried out intensive searching of gardens in Nelson city and surrounding areas to find and remove great white butterfly infestations. The Nelson Tasman community also played a vital role, supporting the eradication programme by keeping watch for the pest, reporting finds and allowing repeated searches of their gardens.
A great white butterfly found in December 2014 turned out to be the last find of the pest. Searches continued until June 2016 but there were no further finds of great white butterflies or of the caterpillars, eggs and pupae.
Following scientific assessment of the eradication effort, DOC and MPI in November 2016 determined the eradication programme had been successful – the great white butterfly was declared to be no longer in New Zealand.
You can help
The great white butterfly is currently not known to be in New Zealand but a watch is still needed should it be found here again. Keep an eye out for the great white butterfly in your garden.
The great white butterfly is most easily identified by its conspicuous caterpillars feeding in groups on its favoured plants and by its clusters of eggs.
If you see any suspected great white butterfly caterpillars and eggs, report it to the MPI hotline 0800 80 99 66.