Southland Regional Council says early tests results show that a parasitic wasp released in the region late last year is killing a devastating pasture pest.
The tiny wasp was imported from Ireland and bred in the laboratory by AgResearch to counter the clover root weevil.
The weevil has been spreading through the country since its discovery in Waikato in the 1990s and was found in Southland early last year.
It causes estimated losses to agriculture of $1 billion a year by destroying white clover, which is an essential part of the pasture of New Zealand farms.
A Southland regional council senior biosecurity officer, Randall Milne, says early tests results show that the wasp has successfully established itself in the region.
A parasitism level of 3% was found in samples of weevils taken from pasture. In spring, when the soil temperature warms up, the wasps will start breeding, Mr Milne says.