Officials battling to contain a Queensland fruit fly incursion in central Auckland have ruled out aerial spraying following confirmation of a fourth fly being discovered in traps.

The Ministry for Primary Industries said today that aerial spraying was not the most appropriate treatment and was not being considered as a contingency option if it emerged the pest had established a wider population here.

It comes after a male fruit fly was found in another trap in the controlled area around Grey Lynn last night.

The find brings the total to four confirmed Queensland fruit flies in a week, with three male fruit flies caught in traps, and a single unmated female located at a residential property on Friday. One pupa and 39 larvae have also been found.

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A spokeswoman for MPI said they were not considering using a technique in which sterile insects were used to lure out the pesky fruit flies.

"That is used for larger scale infestations, not localised situations," she said.

Horticulture New Zealand have said the incursion is a "huge worry" but declined to comment further today.

In a statement provided to NZME. News Service, MPI said there was "no consideration of aerial spraying at all" to deal with the potentially crop destroying pest.

"The appropriate treatment, as outlined on our website and in all our media releases, is baiting, using a protein bait that attracts both male and female fruit flies," a spokeswoman said.

"This contains a very small amount of fipronil insecticide, which is an insecticide used most commonly in pet flea collars.

"On occasions where plants are found to be infested with Queensland fruit fly (identified from fruit inspections), cover spray will be applied to these infested plants using a ground-based applicator. Bifenthrin is the insecticide that will be used in this situation.

"This treatment is safe for use in residential areas because it has been proven to do no harm to people, or animals such as family pets or livestock. Because of this it is one of the most common insect treatments found in products sold in supermarkets and hardware stores."

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The statement will ease fears among those worried the ministry might spray large swathes of Auckland if it is found the pest has established a population here.

Aerial spraying campaigns were used in 1996 to eradicate the white-spotted tussock moth in Auckland's eastern suburbs and, between 1999 and 2003 against the painted apple moth in the western suburbs.

The then Ministry of Agriculture and Forestry's controversial decision to aerial spray west Auckland to combat the spread of painted apple moth was met with anger and protests.

An ombudsman's report in 2007 said officials failed to pay enough attention to the health effects of the insecticide Foray 48B which was used in the painted apple moth outbreak and an Asian gypsy moth outbreak in Hamilton between 2002 and 2004.

- Additional reporting: Claire Trevett of the New Zealand Herald

The story so far:

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- Four confirmed Queensland fruit flies found

- Three male fruit flies caught in traps

- A single unmated female located at a residential property

- One pupa and 39 larvae also found

- MPI not considering aerial spraying or sterile insect technique