Crown Research Institute applies to import wasp biocontrol agent

Environmental risks posed by the giant willow aphid include damaging willow trees, which may affect riverbank stability in the countryside.

New Zealand Crown Research Institute Scion applied to the Environmental Protection Authority (EPA) to import and release the parasitoid wasp, Pauesia nigrovaria, as a biological control agent for the giant willow aphid (Tuberolachnus salignus).

One of the largest aphid species, Tuberolachnus salignus can grow 5.8mm in length. It was first reported in New Zealand in December 2013 in Auckland and has spread quickly across the country.

Environmental risks posed by the giant willow aphid include damaging willow trees, which may affect riverbank stability in the countryside. The aphids transform willow sap into a honeydew. Bees that drink honeydew produced by the giant willow aphid produce sour, unmarketable honey.

The Decision-making Committee considering the application taking into account a range of information, including a total of 50 public submissions; 45 in support, two opposed, and three neither opposing nor supporting the application.

The Committee concluded that the benefits of releasing P. nigrovaria outweighed the potential risks.

It found that the release of the wasp – which does not sting and is not known to pose any risks to people - would provide a highly specific and sustainable tool to control giant willow aphid populations.

It also concluded that:

• the presence of P. nigrovaria would reduce the production of giant willow aphid’s honeydew which is a food source for pest Vespid wasps. These wasps feed on honeybees and compete with native insects for nectar.

• there would be negligible adverse effects on the environment and on ecosystem interactions and food webs. Native aphids would not be at risk.

• non-release of the wasp could have adverse effects on the economy, as high giant willow aphid populations could reduce willow tree growth and carbon sequestration (the process involved in carbon capture and the long-term storage of carbon dioxide in the atmosphere).