The first batch of 500 giant weta are set to be released on pest-free Motuora Island in the Hauraki Gulf today, after an "unprecedented" breeding and rearing success, Auckland Zoo says.

Some 150 of New Zealand's largest giant weta, the weta punga, will be released today and a further 150 of the nationally endangered invertebrates will be released on Tiritiri Matangi Island next month.

They will be followed by another 200 later this year.

A group of adults will remain at the zoo to help breed a second generation.

The weta punga is one of the world's heaviest insects, with some weighing as much as a sparrow.

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The successful breeding programme saw six male and six female weta pungas transferred from Little Barrier Island, the only place they are now naturally found, to Auckland Zoo in May 2012.

The zoo's curator of ectotherms and birds, Richard Gibson, said new techniques involving rearing the insects in groups as well as individually, were trialled within the zoo's temperature controlled weta facility for the first time.

"Because we were hatching so many, we established groups of anywhere from five up to 100 animals, in different sized enclosures," he said.

"It's been a pretty intense period of work for the team, but an absolute privilege to be helping such an iconic threatened species.

"We're delighted to have achieved a 95 per cent success rate in rearing animals individually, and around 50 per cent success rate with the groups - significantly higher than we expected."

The 150 weta being released today are close to adulthood, and it is expected they will begin to breed shortly themselves.

Department of Conservation scientific adviser Chris Green said the weta recovery group's plan was to establish several populations around the Hauraki Gulf, ensuring the survival of the species and their long-term security.

"By using captive breeding we can now transfer several pioneer populations to other islands, improving the chances of the species surviving in the event of a catastrophe on Little Barrier wiping them out for ever," said Dr Green.

- APNZ