8 August 2001

Media Release
North Island Farming Media & Daily Media Farm Pages

Days numbered for clover root weevil

Researchers are near to hitting paydirt for North Island farmers plagued with clover root weevil.

The destructive weevil, which is moving south to now reach a line across the island south of Taupo, may have its days numbered as a severe pest of white clover.

AgResearch’s Stephen Goldson, who leads Lincoln’s biocontrol and biosecurity group, says promising progress has been made on two fronts. The tiny parasitoid wasp Microtonus aethiopoides and the fungus Beauveria bassiana have been identified as two possible control approaches, Dr Goldson says.

The wasp was found last year in Europe in a search which found them living near the weevils. This was the most widely distributed natural enemy of clover root weevil – 9000 of which were found in 15 places in 11 countries. In laboratory trials, the wasp has been found to attack a high percentage of the weevils.

Interestingly, this species of wasp is already in New Zealand, but our particular strain does not attack clover root weevil here.

AgResearch scientists are now breeding up the imported European versions of the wasps in quarantine, and looking at which strains of the wasp are likely to be the most effective. This includes research into their fertility, mating behaviour, longevity, attack rates, development rates and impacts on non-target species.

"We have to make sure the material we are bringing in isn’t going to damage non-target species."

The fungus Beauveria also already exists in New Zealand. It gets between the cracks and chinks in the weevil’s shell and causes disease. But a Welsh version of the fungus is up to 10 times more active than the New Zealand version.

"We are looking at ways of making it into a bio-pesticide by formulating it into pellets. This way we can keep the fungus alive for longish periods. In short, we are experimenting with ways of reliably putting Beauveria into the soil, where it can kill the clover root weevil grubs."

AgResearch’s work into clover root weevil is jointly funded by WoolPro, Meat New Zealand, the New Zealand Dairy Board, the Game Industry Board, and the Foundation for Research, Science and Technology, as well as the Foundation for Arable Research, AGMARDT, the C. Alma Baker Trust and the Lincoln Foundation.

[ends]

For more information, contact:

WoolPro research manager Ken Geenty,
tel 06 356 8611

AgResearch scientist Stephen Goldson,
tel 03 325 6900.