A pest which can destroy entire crops of feijoas and other soft fruits has spread south from Northland and Auckland to Waikato and areas of the Coromandel.
The guava moth arrived in New Zealand from Australia in 1997 and has been causing problems for feijoa growers in Northland and more recently Auckland.
The discovery was made by Plant and Food Research as part of a three-year study into the pest and what can be done to eradicate it.
The traps set earlier in the year detected the bug at properties in Thames, Miranda and Matangi.
The Ministry for Primary Industries also set traps and had positive results in the Coromandel.
Plant and Food entomologist Asha Chhagan said fortunately there were no signs of guava moths in the Bay of Plenty, Hawkes Bay, Gisborne or Nelson.
"They're quite important fruit-growing regions of New Zealand and if this pest was to get into those regions it would be of great concern because it has a wide host range."
It was not a fussy bug and would happily burrow into citrus, plums, macadamias or feijoas, she said.
The study would continue this spring as the researchers try to find out more about the moth's distribution, potential natural enemies as well as what chemical controls would have an effect.
Dr Chhagan was keen to recruit more people to the study who suspected they had been affected by guava moths.
She said they were looking for properties to place traps on in and around the Waikato later this year.