Clover root weevil has been confirmed in the Catlins, Ophir and near Duntroon in the past six weeks.
CRW was first discovered in 1996 in the Waikato and, by 2004, it had spread throughout the North Island. It was first discovered in the South Island early in 2006 and was still spreading.
Farmers were urged to be vigilant and contact AgResearch if they suspected a CRW infestation so the biocontrol agent could quickly reach areas where it was needed. AgResearch first released the tiny parasitic wasp, from Ireland, in 2006.
It was hoped that by getting it released early, while the weevil was still establishing and spreading, it would "knock the top off it", Mark McNeill, from AgResearch, said.
The adult stage of CRW feeds on white clover leaves and the larval stages feed on clover roots. In the worst cases, farmers would lose clover for a short period of time but it would come back.