The larvae of this leaf beetle, in large enough numbers, are capable of stripping the yellow-flowering tutsan plant of its leaves.

Hill country farmers are getting champagne bottles ready to pop following a recent announcement by the Environmental Protection Agency.

The EPA has approved the use of two biocontrol agents – a moth and a leaf-feeding beetle – to help fight the pest plant tutsan.

The yellow-flowering shrub is not toxic, but livestock will not eat it. Removing it is time consuming and costly for sheep and beef farmers.

However, the larvae of a moth from Georgia, Eastern Europe, feed on tutsan leaves and burrow into its fruit, consuming its seeds. The larvae of a leaf beetle, also found in Georgia, strip tutsan plants of their leaves.

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The insects were found by the Tutsan Action Group (TAG) - a grassroots industry organisation that has spent nine years searching for an effective way to fight tutsan.

Rosalind Burton from TAG said the voluntary group undertook a worldwide search for an effective biological control, generously supported by hundreds of farmers.

"We hoped to find one, but we've found two, and we're cleared to release them in New Zealand," she said.

The decision to release the insects came following 18 months of Landcare research in Christchurch, which found the bugs were not a threat to other plants in New Zealand, Burton said.

"[Landcare] do all sorts of technical scoring throughout these tests. While one of the insects did lay eggs on one native species, the larvae didn't do very well," she said.

"[The laying of eggs on a native species] was a reason why DOC, in particular, took it to a hearing. At the hearing, everyone was very supportive of it and Landcare was able to allay any fears that DOC had about native species of hypericum."

Burton said the bugs were being bred in Christchurch and they would be released in spring when warmer weather comes.

"We're talking hundreds of thousands. As time allows, we'll breed more and release more," she said.

"It will improve land values on farms that had tutsan, and improve productivity on those farms."