Quick Dips

Useful Parasites

The release of imported South American parasitoids at Lincoln and Waikato has had a noticeable effect on Argentine stem weevils at the release sites. Nearly 50% of Lincoln weevils and up to 70% of Waikato ones were found to have been attacked.

These results are following predicted patterns, says Dr Stephen Goldson of AgResearch Lincoln, and if they continue to do so, damage from the weevil will be much reduced. It remains to be seen, however, how fast the parasitoids will spread, and weevil populations around the Lincoln release site will be monitored over the winter to get an idea of this.

The parasitoids, tiny wasps the size of small sandflies, are the weevil's natural control in South America. They lay eggs in the weevil, sterilising it immediately and causing eventual death. The sterilisation is important, as it's the larvae rather than adult weevils that cause pasture damage.