A New Zealand-European study has provided new hope that many exotic weed pests around the world can be better treated with exotic insects rather than chemical controls.

The study looked at concerns that non-native insects introduced to control weeds actually began feeding on non-target plants after release, further affecting native ecosystems.

The researchers from the New Zealand government's Plant & Food Research institute and the France-based European Biological Control Laboratory looked at 512 cases of deliberately introduced insect controls around the world dating back more than 150 years.

"A total of 43 weed biocontrol insects worldwide have been reported to feed on non-target plants after release, but the real surprise comes when you look at the level of this feeding and what little effect it is having on the plants, compared with calls for concern about biosafety in the scientific literature," Plant & Food researcher Dr Max Suckling said in a statement Tuesday.

The scientists found decreases in plant reproduction in non- target plants to be very rare and only four insects had caused plant populations to decline significantly anywhere.

"Our analysis shows that as far as is known, weed biological control agents have historically had an excellent biosafety track record, with more than 99 percent of cases avoiding significant non-target impacts on plant populations," Suckling said.

They concluded biological control of weeds by the introduction of specific insects was environmentally sustainable compared with chemical sprays.