The varroa bee mite has been found at several apiary sites outside the controlled area in the north of the South Island.
Previously varroa infected hives existed in an area roughly 20km around Nelson, the only area in the South Island so far hit by the mites which are widespread in the North Island.
But the mite had now been found near St Arnaud, just outside the Nelson-Marlborough varroa controlled area boundary, the Ministry of Agriculture and Forestry Biosecurity New Zealand (MAFBNZ) said today.
The mite was found during the annual MAFBNZ South Island apiary surveillance programme, which began in mid-April.
"Affected beekeepers have put voluntary movement controls in place and are using quarantine and treatment measures for varroa across their operations," MAFBNZ incursion response manager Richard Norman said.
Since its arrival in New Zealand seven years ago - reportedly on a queen bee smuggled into the country - the varroa mite species has spread rapidly, laying its eggs inside the brood cells of a beehive, where the mites develop to maturity by feeding on bee larvae.
Uncontrolled, varroa will usually "kill" a bee colony within a year - an expensive loss to beekeepers as well as a major threat to honey producers and the billion dollar fruit export industry, which relies on bees for pollinating crops such as kiwifruit.
"To protect beekeeping operations from varroa in the West Coast, Canterbury and areas further south, MAFBNZ will replace the current Nelson-Marlborough controlled area with a new controlled area covering the northern part of the West Coast, Buller, Tasman, Nelson, Marlborough, and part of North Canterbury," Mr Norman said.
This was an interim measure and there would be consultation with stakeholders about how to proceed in the future.
The new controlled area was expected to come into force on May 13 and a letter would be sent to all registered beekeepers in the South Island.
Beekeepers directly affected by the new area would be contacted individually in the coming weeks.
Until it is in place, beekeepers were required to adhere to movement controls already in place.
Mr Norman said varroa had also been confirmed at an apiary site in Blenheim, within the Nelson-Marlborough controlled area.
"Beekeepers in and close to the Nelson-Marlborough controlled area are urged to regularly test their own hives for varroa mites on bees or in brood. Beekeepers detecting varroa in their hives should report the find to MAFBNZ via the 0800 80 99 66 free phone number."
Sampling for the annual surveillance programme was expected to be completed in June with final laboratory results expected in July.
Additional surveillance will take place close to the new controlled area boundary to confirm that the boundary has been set appropriately.