Bringing a body snatcher to a paddock near you

As a prelude to the 2015 Beef + Lamb New Zealand AGM at Telford there was a final release for this season of parasitoid infected clover root weevils.

The clover root weevil (CRW) or Sitona obsoletus (previously known as Sitona lepidus) was first found in New Zealand in the Waikato in 1996. CRW has caused severe pastures damage as it spread the length of New Zealand.

Pottles contain parasitized CRW [photo Matt Dewes]

The effect of CRW on white clover is to cause its decline and in severe cases its complete loss from pastures. As a consequence nitrogen fixation is reduced or lost and nitrogen fertilisers have to be applied to maintain pasture production.

Damage to clover from CRW [photo Pestweb]

After an extensive, and slightly serendipitous, search in Europe for a potential biological control agent, and biosafety testing in a containment facility in New Zealand, a parasitic wasp was approved for release by the Environmental Risk Management Authority (now the EPA) in 2006.

The parasitic wasp or parasitoid, Microctonus aethiopoides, approved for release consists of one biotype collected in Ireland which reproduces parthenogenetically, that is it does not require males and all of the offspring are females. This CRW biotype is known as the Irish biotype.

The Irish biotype has established quickly across the North Island and has been very effective in controlling CRW. As CRW has moved down the South Island the parasitoid has followed. CRW finally reached Otago and Southland in 2010 and due to mild winters it quickly built up so that by 2013-2014 it had reached epidemic proportions in some places.

In response to CRW outbreak an AgResearch team, with support from Beef+ Lamb New Zealand and DairyNZ, spent the late summer and autumn of 2014 releasing over 550,000 parasitised CRWs at about 4000 sites across Otago and Southland. In additional, farmers could come to AgResearch’s Invermay farm and collect parasitised CRWs for themselves and around 250,000 were collected in this way.

Colin Ferguson and farmers, Telford field day [photo Matt Dewes]

According to AgResearch scientist Colin Ferguson “dispersing the wasps will significantly accelerate spread of the biocontrol agent and allow clover recovery to begin”. It is anticipated that the clover content of pastures should return to normal in two to four years and returning, based on the North Island experience, benefits of over NZ$57 per hectare per year (Bio-Protection 2014).

You can read more at:

AgResearch 2012. Irish wasp more than match for clover root weevil. AgResearch News. Link here

Beef +Lamb New Zealand’s chairman James Parsons’ address to the 2015 annual meeting, held in Balclutha on Wednesday 11 March. Link here

Bio-Protection 2014. Saving New Zealand pastures from pests. Bio-Protection Research Centre, Annual Report 2014, page 29. Link here

Environmental Risk Management Authority 2006. Biological control of clover root weevil. Link here

Pestweb. Clover root weevil. Link here

Other B+LNZ resources

Party time for clover root weevil (November 2014) Link here

Combating clover root weevil. Fact sheet (January 2014) Link here

Beef and Lamb Conference – Mark McNeil – Update on the Clover Root Weevil (June 2013) YouTube Link here

Clover root weevil. A major problem for New Zealand (September 2008) Link here