The Clutha-based Californian thistle Action Group (Caltag), in association with Landcare Research, will make the first New Zealand release of Apion onopordi on the large sheep and beef farm of Allan and Sonia Richardson near Heriot in West Otago.
Landcare Research staff will release the first 60 weevils, which are the result of a careful breeding programme at its Lincoln facility near Christchurch.
The Clutha Agricultural Development Board has been administering the Ministry of Agriculture and Forestry sustainable-farming fund project for Caltag.
Project manager Malcolm Deverson said the weevils had not been good breeders and had taken two seasons to reach the numbers needed for release.
"There's every chance they'll breed much more successfully out in the field, although it may be quite a few years before we see them again."
The weevils were much smaller than the other Californian thistle biocontrol agent, the thistle beetle, which was released on a Waitahuna farm in November 2007.
The weevils attack the base and stems of the thistle plant, and Mr Deverson said plenty of evidence had shown they severely weaken the growth and spread of the thistle in Switzerland, where the weevils were sourced.
Caltag chairman Riana Ross, a Catlins sheep and beef farmer, told the Otago Daily Times he was thrilled at the project's progress.
"Caltag has had lots of people involved for over 10 years and it's good to see some positive steps with these agents.
"They'll take a while to have any sort of impact but at least these insects are an important part of a sustainable, long-term solution."
The West Otago launch is one of two planned in the South next week.
Environment Southland biosecurity staff will also release the weevils in the Hokonui Hills near Gore.
