The Ministry for Primary Industries says the first results are expected on Sunday from extra traps being set up in Whangarei following the discovery of a Queensland fruit fly.
Warning signs have gone up in one of the biggest supermarkets inside the city's new biosecurity zone.
There is a ban on taking fruit and vegetables outside the area after a sole male Queensland fruit fly was found on Tuesday. The ban covers parts of the Town Basin in the central city.
The insect is considered one of the biggest threats to New Zealand's $4 billion fruit and vegetable export industry.
The ministry activated a trapping system on Thursday which it says is the best method for identifying male flies. None were trapped overnight on Thursday.
Sixty staff put out more surveillance traps and inspected gardens and rubbish bins for any signs of the pest on Friday. Special bins have been provided to 92 properties within the affected area for residents to dispose of any fruit and vegetables.
A portable laboratory used to check for fruit fly eggs or lavae in fruit samples should be fully operational by Saturday. The ministry says that is the best way to determine whether there are any females flies in the area.
The results from those first lot of traps had initially been expected back by Saturday but are now due back early on Sunday.
The area under control stretches 1.5 kilometres from where the Queensland pest was discovered in a surveillance trap near the Town Basin. It includes the Countdown supermarket at the Okara shopping centre.
Countdown is expecting fruit and vegetables sales at the store to fall significantly and is preparing for controlled disposals of produce. It says spoilage is unavoidable and it is working with the ministry on how to get rid of that waste.
The supermarket chain is putting more produce in its two other Whangarei stores. A spokesperson said customers were responding well.
It's the fourth time a Queensland fruit fly has been found in New Zealand. The last time was in Auckland in 2012.