The Ministry for Primary Industries is still trying to establish how a fruit fly found in Whangarei got into New Zealand.
The discovery of the single male fruit fly about two weeks ago caused a major quarantine response but the ministry has lifted restrictions on moving produce in the area.
The last time a fruit fly was found was in April 2012, near Auckland.
Ministry deputy director general of compliance and response Andrew Coleman said finding just a single fruit fly was not unexpected.
The past four times a fruitfly had been found through the surviellance system it had turned out to be a single male.
"So it's not surprising that we've ended up with just the one," he said.
"The assurance that we put in place, it might seem to be quite rigourous but it has to be ."
That was because if more were found, the movement of fruit and vegetables would be restricted.
"But more importantly, for New Zealand's trade, is that we're convincing the international trading partners of New Zealand that for fruit fly, and the status of being free from it in New Zealand, we've actually maintained that through this process."
The ministry still did not know how the fruitfly got into New Zealand, which Horticulture New Zealand president Julian Raine said was a concern.
"The most likely is it's coming in on a passenger, with a bit of random fruit in their luggage. It could have come in, this particular one, from a visiting yacht because part of the area was where visiting yachts do come into Whangarei harbour," Mr Raine said.
It was also possible it had come in on commercial produce from Australia, although that was less likely.
The industry and the ministry needed to review whether the regulations and monitoring for fruit flies and other exotic pests are good enough at the border, he said.