Sharp-eyed border security at Dunedin airport in New Zealand may well have saved the country’s horticulture industry millions of dollars.

New Zealand's horticulture industry has today expressed its gratitude to the security officials who picked up a single mandarin carrying a fruit fly maggot.

The discovery of the Queensland fruit fly in New Zealand would have jeopardised the commercial fruit and vegetable export industry, valued at around £1 billion.

According to Hort NZ, the Queensland fruit fly is the single most threatening pest facing New Zealand horticulture. It occurs in so few countries, its discovery in NZ would mean most of the more than 100 countries growers export to would close their borders to Kiwi produce, said HortNZ ceo Peter Silcock.

The maggot was in an undeclared mandarin carried by an Australian tourist. The tourist was fined NZ$200.

"One mandarin carrying Queensland fruit fly maggots - that's all it takes to start a chain of events that could threaten millions of dollars in export earnings and thousands of jobs in this country,” said Silcock.

“Eradication of such a pest would also cost millions and it could take more than a year for international markets to reopen to our produce.”

A study commissioned by the horticulture industry last year into the threat posed by another type of more common fruit fly showed the Bay of Plenty alone could lose annual income of $820m.

"As we've always suspected, it is uneducated international travelers coming into this country who are the greatest risk of carrying such pests,” Silcock said.

"That's why it is extremely reassuring for us to see the system working in this case and we remain extremely concerned that increasing the number of international airports in New Zealand will only increase this risk.

"We congratulate the Dunedin Airport biosecurity staff on a job very well done, and thank them for their vigilance."