The Ministry for Primary Industries says another fruit fly has been found in Auckland, pushing the total number found to five.
Five Queensland fruit flies have been found in the suburb of Grey Lynn, as officials continue to bait traps and check fruit from within a biosecurity cordon.
The Minister for Primary Industries said one more male was found today in a trap within 200 metres of the Grey Lynn property.
It said the find was not a significant development, as it expected to find more flies near the property.
About 120 field staff have been out today applying insecticide bait throughout the area and looking for any other flies trapped in the ministry's surveillance trapping system.
Earlier, the Minister Nathan Guy said he was confident the isolated fruit fly population would be eradicated.
"You know, we've got a world-class biosecurity system but human behaviour, the way it is, people unknowingly bring things in or knowingly smuggle things in."
Mr Guy said it was possible it might never be known how the fruit flies got into New Zealand.
But Labour's Primary Industries spokesperson Damien O'Connor said calling the biosecurity system world class was an idiotic statement.
"The system has failed and no matter how many times Nathan Guy or John Key say so - it is an example of the Government's stupid managment of one of the most important responsibilities of this Government."
Mr O'Connor said a Labour-led Government would re-introduce 100 percent screening of incoming baggage.