Millions poured into Queensland fruit fly fight, but the cost is defended as necessary to protect export industry

A close-up shot of a Queensland fruit fly on a feijoa leaf. Photo / File

More than $4 million was poured into the fight against the Queensland fruit fly scare in Auckland between February and June 15. But Biosecurity New Zealand told the Herald the cost was a necessary evil.

"[That] sounds like a lot to spend in a short space of time but [not] when you consider what you're protecting," spokeswoman Dr Catherine Duthie said.

"We're talking about the protection of a multimillion-dollar industry, probably costs into the billions, that could have been affected."

Figures obtained from the Ministry for Primary Industries through the Official Information Act revealed 13 fruit flies were found at a total cost of $4.1 million.

New Zealand was most at risk of the pest making its way to the country during the Australian growing season - our summer months.

The first Queensland fruit fly was found on February 14 in Devonport.

Another nine were found in Northcote, on February 20, 23, 28, March 4, 10, 14, April 25, May 10 and 31.

Elsewhere, three Facialis fruit flies, which originate from Tonga, were found in Ōtara on February 18, 21 and March 5.

Duthie said most of the costs were attributable to staff hours as "huge manpower" was needed to take on the fruit flies.

She said Biosecurity NZ teams worked to an international standard and she was confident in their methods of trapping.

"We're really happy with our surveillance system, we've put in the appropriate controls when we do find one of two or three flies.

Biosecurity surveillance coordinator Kerry King working in Devonport. Photo / Michael Craig

"We're very confident that we can detect flies at very low areas, the flies in that area we will catch with the technology we have available."

The traps only attract males and have a particular cue which told them there was a potential for mating in the area.

No females had been caught during the campaign, Duthie said.

"The poor lab technicians have cut up tonnes of fruit and dissected it and they have not found any evidence of eggs or larvae in that."

No homes were sprayed during the response but operations included the application of an insecticide bait.

Baiting, unlike trapping, was attractive to both females and males and between March and June Biosecurity NZ staff visited 19,494 homes on the North Shore.

The total number of homes visited in Northcote was 5238, 6301 in Birkenhead, 6329 in Northcote Pt and 1626 in Chatswood.

Two components were used in the bait, a protein to attract adult fruit flies and a very low concentration of the insecticide fipronil to kill the insects.

The amount of fipronil was similar to the amount used to treat a large dog for fleas.

Over winter, Queensland fruit flies still in Auckland would be hiding underneath leaves and waiting until the warmer weather came back to the region.

Duthie said it was hard to discuss whether the campaign had been successful, a better picture would be painted in spring, but action needed to be taken.

"It's not really about the number of fruit affected although that would be the direct impact, it's the indirect impacts we're trying to protect," she said.

Rod Emmerson's take on the fruit fly discovery. Photo / Rod Emmerson

"We have a huge competitive advantage because New Zealand hasn't got any fruit flies ... that would cause other countries to put restrictions on our export fruit.

"That gives us a massive market advantage because we have lower insecticide usage, which gives us access to markets we wouldn't otherwise have such as Asia."

Queensland fruit flies are reddish-brown with distinct yellow markings, clear-winged and usually between 6mm and 8mm long, a little larger than a house fly.

Native to the state of Queensland, the fruit fly has already found its way to other parts of Australia, New Caledonia, French Polynesia and the Pitcairn Islands.

Adult fruit flies lay their eggs in fruit and when the maggots hatch, they eat the fruit which causes it to rot.

Their favourite fruits are guava, stonefruit, tomatoes and mango but the maggots have been known to eat over 200 different types of fruit and vegetables.

Their lifecycle tended to be about one year, except in warmer areas where there could possibly be two generations in a year.

Biologically speaking, to have an established generation there would have to be evidence of two separate generations, Duthie said.

"So look at eggs and larvae this year, and then breeding has occurred and then next year they find eggs and larvae again," she said.

Biosecurity NZ would not be drawn on what insecticides might be used in the hypothetical event of the fruit fly becoming established here.

But several chemicals used to control the fruit fly in Australia, such as clothianidin and chlorpyrifos, face potential bans in the European Union.

"Living with fruit fly would be different from responding and attempting to eradicate," Duthie said.

"Chemicals for use in management of fruit fly would potentially be different depending on regulatory requirements for withholding periods and residue levels."