While only a few millimetres long, the tiny parasitic wasp from Ireland is already making big hits on clover root weevil infestations in several North Island localities. Known as Microctonus aethiopoides, the wasp has been released to help control the 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 has since spread throughout the North Island and now into the South with infestations confirmed in the Nelson region.

Speaking at the re-inaugurated Ruakuara Farmers’ Day, Dr Pip Gerard reported that the wasp was performing above scientists’ wildest expectations. “We released the parasitoid at experimental release sites in Waikato, Hawke’s Bay and Manawatu in January and February and to recover parasitism levels of 11 to 16% at all these sites by May is extremely exciting. Based on our experience with the Argentine stem weevil parasitoid, we weren’t expecting these levels till next year”. However, she did sound a word of caution. While optimism is high that the biocontrol programme is going to be successful, scientists won’t know till next summer if enough wasps will make it through the New Zealand winter to reduce weevil populations.

Plans are underway to establish “nursery” release sites in all regions where clover root weevil is a problem. “We’ve yet to find out how fast the parasitoid spreads and therefore the best strategy to get it to all farms” said Dr Gerard, “but these nursery sites will help whether the wasp spreads quickly by itself or needs assistance”.

A release in the Nelson region is being fast-tracked by Dr Craig Phillips and his team from AgResearch at Lincoln. “We have the opportunity of getting the wasp into this clover root weevil hot-spot before the weevil spreads any further, and we are thankful for the support of Dairy Insight, and Meat & Wool New Zealand. Hopefully this will slow the spread of the weevil and prevent South Island farmers having to suffer the wave of damage North Island farmers experienced soon after it invaded their districts.