Wellington, May 21 NZPA - Biosecurity officials at the border have impounded Queensland rock melons infested with fruitfly eggs and ordered them re-exported or destroyed.

Cucumber fruitfly eggs were found in a single container, which also contained zucchini and beans, being cleared for entry to New Zealand.

The pest is found on zucchini, rockmelon, honeydew and watermelon.

The find showed border protection systems were working, Ministry of Agriculture and Forestry's biosecurity group manager for plant imports and exports Stephen Butcher said.

"Fruitfly is present in many areas of Australia and we require all produce from these areas to be treated before export to New Zealand," he said.

Rock-melons were supposed to treated after harvest and before export.

"We have asked the Australian Quarantine Inspection Service to investigate whether this happened or if the treatment failed," Dr Butcher said.

MAF does not inspect every piece of produce but checks samples from every consignment.

Other imports of fresh produce using the same treatment system from Queensland, have been suspended until investigations by New Zealand and Australian authorities are carried out.

A fruitfly incursion in fruit-growing regions would have a significant effect on the New Zealand economy with major impacts on exports, potential job losses and a bill for eradication costing millions of dollars.

"An incursion here could result in our trading partners suspending horticultural exports from New Zealand," Dr Butcher said.

Biosecurity Minister David Carter said the interception was a "smart action" by border inspectors and followed another interception of unidentified fly eggs in a consignment of oranges from California on Tuesday.

That fruit was impounded and fumigated immediately.

"In the case of the fruit from California, a small black spot on one of 600 oranges was detected," Mr Carter said. "It was like finding a needle in a haystack."

Federated Farmers congratulated MAF on the interception, and its biosecurity spokesman John Hartnell said the Queensland fruitfly could have had "dire consequences" for the horticultural industry.

In the mid-1990s, discovery of Mediterranean fruitfly saw China block New Zealand fruit for a year.

"Federated Farmers fully supports moves to halt imports from Queensland until we get some cast iron assurances," Mr Hartnell said.