Horticulture New Zealand says the discovery of a third Queensland fruit fly is concerning, but it is confident the pests will be eradicated and the country's export markets will not be affected.
The Ministry for Primary Industries (MPI) said a resident living in Zone A of the controlled area trapped and reported the female fly after discovering it on his lemon tree.
MPI chief operations officer Andrew Coleman said investigators immediately visited the property, where they found lemons and plums containing Queensland fruit fly larvae.
Horticulture New Zealand chief executive Peter Silcock said all efforts needed to be focused on establishing the size of the population and eradicating it.
"We are actually confident, these look like they're coming through the same source, they're close together and therefore we're confident that the work MPI is doing out in the field is going to eradicate this," he said.
"We haven't had any indications at this stage from (export) markets, I think they understand that we're doing all that we should be doing, following really international protocols around this and how people respond to fruit fly finds in their countries.
"So we're expecting them to accept what we're putting forward and the assurances that MPI are providing."
The Ministry for Primary Industries said traps were being set, and bait to capture and kill female fruit flies was being applied to trees. There would also be spraying under fruit trees where the pests had been found.
It said airports were also under stricter controls, with detector dogs screening all international passengers and their luggage.