Two more fruit flies, including a dead one, have been found in a central Auckland suburb - bringing the total to three.

The Ministry for Primary Industries (MPI) today confirmed an isolated population of the Queensland fruit fly was found.

A Grey Lynn resident found a single fly in a lemon tree on his property, captured it and reported it to the ministry.

"The fly was formally identified as a recently-emerged un-mated female adult fruit fly. This is the only fly that has been found, over and above the initial trapped fly found earlier this week," MPI said in a statement.

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Andrew Coleman, the ministry's chief operations officer, said the resident who captured and reported the fly has allowed MPI to act swiftly to scope the problem.

"Our investigators immediately visited the property concerned where they found lemons and plums containing Queensland fruit fly larvae," Mr Coleman said.

"In total, at close of operations last night, MPI confirmed that one fly, 39 larvae and one pupa had been found at the property."

The Ministry said it and its response partners, including PipfruitNZ, were now deploying significant resources to respond to the detection.

"We have every confidence that treatment will quickly and effectively eradicate this population. We have successfully eradicated previous incursions of fruit fly - notably the Mediterranean fruit fly in Auckland in 1996," Mr Coleman said.

He said initial treatment would involve placing bait in fruiting trees to attract and kill female fruit flies. The bait will be applied high up in trees and plants, away from children or pets.

"A second line of treatment will involve some targeted ground-based spraying of areas under fruiting trees where positive finds have been made. This involves using an insecticide that is safe for use in residential areas and has been proven to do no harm to people or animals such as family pets or livestock."

He said no use of aerial spraying would be needed.

MPI said existing controls on fruit and vegetable movements remained largely the same with the previously defined "wider controlled area" unchanged.

"The only change is to the scale of the higher-risk Zone A which has been slightly extended. This will be communicated to the Auckland public as soon as possible," the Ministry said.

Whole fresh fruit and vegetables, except for leafy vegetables and root vegetables, cannot be moved outside of the defined area.

An additional export restriction zone now extended for 3.5km from the location of the last detection. Produce susceptible to fruit fly grown within this zone cannot be exported, MPI said.

New Zealand markets for horticultural produce were also told about the situation.

Mr Coleman said since Tuesday, MPI had introduced "more stringent risk assessment" of cargo, craft, mail and passengers.

International air passengers' luggage was now going through x-rays and an MPI detector dog was screening luggage.

"This could mean some minor inconvenience for inbound passengers, but is necessary given the risk to New Zealand," MPI said. "If it became established here, the Queensland fruit fly could have serious consequences for New Zealand's horticultural industry. It can damage a wide range of fruit and vegetables and could lead to restrictions on trade in some of our horticultural exports. It can also have impacts on home gardens."

The discovery of more Queensland fruit flies inside an already-established protection zone is "very concerning" but not unexpected, Horticulture New Zealand says.

The new find was less than 200m from where the first fruit fly was found and was almost certainly from the same source.

"We are confident this localised detection will be swiftly and effectively eradicated," said Julian Raine, Horticulture New Zealand president.

The group welcomed "improvements" in border controls the Ministry for Primary Industries announced today.

"That's going to provide a lot of confidence to our members," Mr Raine said.

His organisation said the entire New Zealand horticulture industry owed a deep debt of gratitude to residents of the affected Grey Lynn areas.

"We can't thank these people enough for their concern and their vigilance," Mr Raine said.

All efforts must now be focused on establishing the extent of the population, containing it and then eradicating it, Horticulture New Zealand added.