Growers in Northland are hoping the Ministry for Primary Industries has successfully restricted the Queensland fruit fly infestation in Auckland.
Kerikeri orchardist and chairman of NZ Citrus Growers Inc, Rick Curtis, said the discovery of a female fruit fly in Grey Lynn might mean a breeding population is present.
An infestation of Mediterranean fruit fly in the suburb of Mount Roskill in 1996 also included a female.
Mr Curtis said that incursion was eradicated, and growers in neighbouring Northland are confident this one will be, too.
"It's more concern than it is for a single male fly, obviously, because it signifies that you might have a breeding population, but (the infestation) is small and we've had this before and successfully eradicated it.
"The Queensland fruit fly is spreading right throughout Australia, and its good from our industry's point of view to see MPI acknowledging the increased risk and moving to improve surveillance x-ray and the use of sniffer dogs on inbound luggage from Australia."
The Ministry for Primary Industries confirmed yesterday a fourth fruit fly was discovered in the Auckland suburb of Grey Lynn, and believes it to be part of the same localised population as previous detections.
A control zone covering a circle 1.5km from the official find, and a wider 3.5 km export restriction zone are in place. Fresh fruit and vegetables cannot be moved out of the 1.5 km control zone.
The Queensland fruit fly, Bactrocera tryoni, is considered Australia's worst inspect pest of fruit and vegetable crops, and infestations devasated citrus crops. An outbreak of the insect pest in New South Wales in 1940-41 ruined 5-25 percent of the harvest.
In Australia, it inhabits parts of Northern Territory, Queensland, New South Wales and the eastern corner of Victoria, with outbreaks in South Australia.
It has been recorded on more than 100 species of fruits and vegetables - along with citrus it has infested apples, pears and peaches, and has been found on tomatoes and cucumbers.
The adult flies grow 6mm to 8mm and can live for many weeks, some times months. A female can lay several hundred eggs in a lifetime.