The Ministry for Primary Industries says it's unlikely a plant pest recently detected in New Zealand will be able to be eradicated.
Two populations of the tomato red spider mite were found near Auckland Airport in late May.
That prompted a biosecurity response which has since led to the mite being found in other parts of the city.
The tiny mite feeds on plants in the Solanaceae family, including tomatoes, potatoes and eggplants, as well as beans, kumara and some ornamentals - roses and orchids. In large groups, they can mummify plants, wrapping them up in silk webbing and feeding on the plant until it dies.
In June a technical advisory group was assembled to provide advice on the mite, its potential impacts, and the available tools and techniques for eradication or control.
David Yard, principal advisor for biosecurity responses at the Ministry for Primary Industries, said as part of the response it surveyed 541 sites of interest to see how far the mite had spread.
"The survey is now complete and the results indicate that the mite has now been detected in eight sites across central Auckland, which cover an area of approximately 91 kilometres squared.
"The findings of this survey therefore suggest that eradication or stopping the spread is unlikely to be achieved, in particular because this mite is carried by the wind and by humans."
During the survey, no mites were found in horticultural production sites. Yard said MPI was in discussion with industry about whether existing control measures that they had in place for other pests would also help manage the tomato red spider mite.
Yard said the mites were tiny, about the size of a full stop, and very difficult to see with the naked eye. It may never be known how exactly the mite entered the country or when it arrived, he said.