AgResearch entomologists are buzzing with excitement after confirmation that a tiny parasitic wasp from Ireland, released in North Island trial spots earlier this year to help counter pasture pest clover root weevil, has established itself at their Hawke’s Bay experimental release site about 30 km north-west of Napier.

This comes on the heels of the discovery of an established population of clover root weevil on a dairy farm in Richmond, near Nelson. The planning of a coordinated South Island response to clover root weevil is underway but the extent and timeliness of the response will be dependent on funding.

“We released the parasitoid at a farm in Patoka on 26 January, and to recover the progeny from those initial females already is extremely positive,” programme leader, Dr Pip Gerard, said.

Dr Cor Vink, a molecular biologist with the AgResearch Biocontrol & Biosecurity team at Lincoln, was able to confirm that the tiny wasps recovered from the release site were the descendants of a female collected in Galway, Ireland, in March 2004 by his colleague Mark McNeill.

Known as Microctonus aethiopoides, the wasp has been released to control the clover root weevil which is a severe pest of white clover, with conservative estimates putting the cost of white clover damage caused by clover root weevil at more than $300 million a year. Clover root weevil was first discovered in Waikato 10 years ago and until recently was not thought to have established itself in the South Island.

The weevil larvae attack white clover roots and nodules underground, limiting nitrogen fixation and clover growth, especially in spring and early summer. Farmers have observed that livestock have slower weight gains and lower milk yields on infested pastures unless fertiliser levels are increased to compensate. The parasitic wasp, which is totally harmless to humans, kills clover root weevil by injecting it with an egg which makes female weevils sterile. This breaks the weevil life cycle. The wasp larvae go through four stages with the last larval stage killing the weevil as it breaks out of the weevil’s body. The larva then turns into a pupa which in turn becomes an adult wasp to start the next generation.

The Hawke’s Bay site is one of four experimental release sites in the North Island that are being closely monitored to determine what will be the best way to get the biocontrol agent to all affected farms as quickly as possible.

“This is a neat result...we are so pleased we have them on the way at Patoka,” said independent consultant, Mike Slay, who monitors the Hawke’s Bay site for Dr Gerard’s team at Ruakura.

The research supporting the parasitoid release is currently funded by Dairy Insight, Meat & Wool New Zealand and the Foundation for Research Science and Technology.