Northland growers have welcomed comments by Prime Minister John Key that yachts from Australia may be fumigated to keep Queensland fruit fly out of New Zealand.
A team of about 80 biosecurity officials has been sent to Whangarei after the discovery on Tuesday of another male fruit fly in a surveillance trap in the suburb of Parihaka, 400 metres from where one was found in January this year.
The insect is considered one of the biggest threats to the country's horticulture industry.
Mr Key said on Friday questions will have to be asked about whether there are any faults in New Zealand's biosecurity system and the Government is taking the matter seriously because the latest incursion is not related to the one in January.
He said the Government would look into the fumigation of private yachts if the fruit fly was found to have entered the country that way.
Rick Curtis, the Northland director of the Fruit Growers Federation, said the site of the first find is directly above the marina and he strongly suspects that is where the pest came from.
"There are no shipments of fresh fruit and vegetables arriving from Australia or anywhere else at Whangarei. They come into Auckland and are then distributed by truck. So I would suspect it's very likely that first one initially has come off a yacht."
Mr Curtis said fruit growers are struggling to control several pests that have entered the region in the past decade.
The Ministry for Primary Industries said the fact that the fly was detected and caught shows its biosecurity systems are working. Compliance head Andrew Coleman said 600kg of fruit was dissected in January and ministry staff did not find a single egg or larva, which would indicate a breeding population.
However, Rick Curtis said that is only partly true. He said Queensland fruit flies should not be getting into New Zealand in the first place - and whatever systems are in place to keep them out are clearly ineffective.
Kiwifruit Vine Health also said more could be done to manage the risk of pests coming into New Zealand. Chief executive Barry O'Neill wants more attention paid to cruise ship and airport arrivals.
He said the current system has about 7500 fruit fly traps - about half set up specifically for Queensland fruit fly - and questioned if that is enough.
"We have been raising with MPI the concern that we may not have sufficient traps in some of our key horticultural areas - both to detect flies early enough but also for regions that don't have fruit flies, when a fly is found somewhere else, say in Auckland, to be able to absolutely assure our markets and our industry that the fly hasn't established in other parts of New Zealand."
In 1996 during a breeding fruit fly discovery in Auckland, China banned fruit from the whole of New Zealand.
"With our trade to China having increased significantly since 1996 that reaction would have a devastating impact on our and other horticultural sectors," Mr O'Neill said. "But there is a significant difference because at this stage we are only dealing with a single male fly. We don't have a breeding population."