New Zealand is the first country to wipe out invasive butterfly

Entomologist Richard Toft searching for great white butterflies in Nelson, New Zealand

Tim Cuff/Alamy

By Alice Klein

Bye bye butterfly. New Zealand has become the first country to successfully eradicate an invasive butterfly species.

The great white butterfly (Pieris brassicae) is found in Europe, Africa and Asia. A member of the species was spotted in New Zealand for the first time in 2010.

An elimination plan was soon launched by the government to protect agricultural crops from being destroyed by the invaders.

Before morphing into a butterfly, P. brassicae starts out as a caterpillar that feeds voraciously on brassica crops – including cabbage, broccoli, cauliflower and Brussel sprouts. It can also eat New Zealand’s 79 native cress species, 57 of which are at risk of extinction.

“The caterpillars feed in groups on a wide range of host plants and will completely defoliate a plant, and can travel more than 100 metres to find another,” says Jaine Cronin at New Zealand’s department of conservation.

Without swift intervention, the butterfly was predicted to spread rapidly through the country.

Bounty hunters

Between 2010 and 2014, the department of conservation carried out more than 263,000 searches of 29,000 properties in Nelson on the South Island, where the pest was first discovered, to wipe them out. The species is thought to have arrived by ship at the city’s port.

To encourage children to join the eradication effort, the department also offered a NZ$10 bounty for every dead great white butterfly brought in during the 2013 spring school holidays.

Children captured 134 great white butterflies, while department staff caught 3000 butterflies, pupae, caterpillars and egg clusters. Killing was done by hand or using insecticide spray, and care was taken not to destroy any native butterfly species. Wasps that attack P. brassicae were also released in 2015 to bolster the efforts.

Banished from New Zealand

S Sepp/New Zealand Department of Conservation

Since the NZ$3 million campaign finished in December 2014, careful searches have not found any more great white butterflies. “We’re confident we can declare them eradicated,” says Primary Industries Minister Nathan Guy.

“If none have been seen for two years despite intensive searches, that is a reasonable claim,” says Myron Zalucki at the University of Queensland, Australia.

The success of the programme was probably down to the butterflies being plucked out early, he says. In countries like Australia and the US where pest butterflies are widespread, it has not been possible to eradicate them. Similarly, another pest butterfly in New Zealand – the small white butterfly (Pieris rapae) – is believed to be too firmly established to eliminate.

New Zealand’s great white butterfly eradication is part of a larger scheme to remove all introduced pests. In July, the government announced that it would also wipe out all rats, stoats and possums by 2050.

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