An international study into the use of introduced insects to control weeds has found little evidence of them going wrong.
Dr Max Suckling of Plant & Food Research said there had been concerns about introducing non-native insects as weed biocontrols because of the risk of them attacking non-targetted plants.
But Dr Suckling said their worldwide survey of more than 500 insect biocontrol cases, dating back more than 150 years, had found few examples of them causing serious damage to other plants.
"What we found was it's actually very rare that the introduced insects will actually have an impact on, say, plant reproduction that is reducing the population of a non-target plant," he said.
"They are successful quite often on the target but not every time. But the point is that they're not having a big impact outside of what they're supposed to do."
Dr Suckling said the study found 43 cases where weed biocontrol insects fed on non-targetted plants after release, but only four cases where they caused serious losses in those plant populations, and none of those was in New Zealand.