The Department of Conservation says searches for the great white butterfly over the next four months will help establish if the pest has been successfully wiped out in Nelson Tasman.
More than a year has gone by since the last great white butterfly find - a male butterfly caught on 16 December 2014.
DOC Great White Butterfly Project Manager Michael Shepherd said finding no butterfly infestations for 14 months was encouraging but experts advised more searching and time without detections were needed to establish if the pest has been eradicated.
"Our rangers have carried out nearly 90,000 property searches since the last find of the pest butterfly. It's great that with all that search activity no great white butterflies, eggs or caterpillars have turned up.
"But we need to do another round of searches through autumn, one of the peak periods for butterfly breeding, to make sure there aren't some remaining butterflies that have escaped detection.
"The fantastic support of the Nelson Tasman community has helped us get to this point and we thank the community for that support. We ask that people still keep an eye out for the eggs, caterpillars, butterflies and pupae in their gardens and to report any found to the Ministry for Primary Industries hotline 0800 80 99 66. DOC rangers will then respond.
"If there continues to be no butterfly detections over the next four months, we will then consult with our expert advisors to assess what the likelihood is that the Nelson Tasman great white butterfly population has been eradicated."
The DOC-led effort to eradicate the great white butterfly was launched in November 2012. The eradication programme aims to clear the pest from Nelson Tasman, where it has only been found, and to stop it spreading to the rest of New Zealand. The butterfly poses a threat to endangered native cresses and to commercial and home brassica crops, including dairy and sheep forage crops.