A tiny Irish wasp can now be used as a biological control agent against clover root weevil, following permission from the Environmental Risk Management Authority (ERMA).
The parasitoid wasp (Microctonus aethiopoides) is 2-3 mm long and is not harmful to humans. It kills the weevils by injecting them with its eggs, which go through four larval stages before hatching and ‘breaking out’ of the weevils’ bodies, eventually killing the weevil. One wasp can attack up to 60 weevils.
The weevil (Sitona lepidus) is a recent invader to New Zealand. The larvae feed on the roots of white clover, causing significant declines in pasture quality. It is a now considered to be a major white clover pest, and is thought to threaten the sustainable production of clover in New Zealand.
White clover is an important crop because it plays a role in nitrogen fixing and contributes greatly to the nutritional value of pasture, Dr Stephen Goldson of AgResearch says.
The parasitoid wasp was first found near Galway in Ireland. It reproduces asexually and only females will be released.
Host range testing
Before being considered as a biological control agent, it was important for scientists to determine if the parasitoid wasp will only attack clover root weevil. This testing was carried out by Mark McNeill and John Proffitt of AgResearch.
Detailed research in quarantine had shown that a small number of native weevils are potential targets for attack by the parasitoid, but that clover root weevil is always the preferred host. Results with a similar parasitoid showed that despite laboratory test results impacts on native species in the field are minor.
The host range testing results underpinned a successful application to ERMA to release this biological control agent in New Zealand.
The final decision is on the EPA website from the new organism register of applications and decisions.
Activity idea
In the unit plan Biocontrol in action students carry out a practical investigation to help AgResearch scientists monitor the spread of Microctonus aethiopoides and its success as a biocontrol agent for clover root weevil.
