The Ministry for Primary Industries says restrictions caused by the discovery of Queensland fruit flies in Auckland are likely to last until November.
The Ministry said it needed many months to be sure the pest was wiped out and it would be working over a long haul to ensure this.
It said it would need to apply bait regularly to attract and kill any other flies.
The Ministry expected to stop baiting in early June because of winter, but said it would need to start again in spring, and said controls on the movement of fruit and vegetables would continue.
The Ministry first thought restrictions might have lasted as little as a couple of weeks after the first fruit fly was spotted in February.
But since then, 14 fruit flies had been found - the last more than a month ago.
While larvae in fruit were last seen on 13 March, there was no indication that the flies had been eradicated, the Ministry said.