Wasp released to control gumleaf skeletoniser

25 January 2011

Crown Research Institute Scion today released a parasitic wasp in Auckland Domain to control the gumleaf skeletoniser, a caterpillar that has become a serious pest in Auckland parks.

The gumleaf skeletoniser Uraba lugens is an Australian insect that has the potential to defoliate thousands of hectares of Eucalyptus plantations as well as ornamental eucalypts grown for shade and shelter throughout New Zealand.

Scion entomologist Dr Lisa Berndt says repeated defoliation by this pest can slow the tree’s growth, or even kill individual trees.

“It’s a very serious threat to our eucalypt forests. Outbreaks occur regularly in Australian forests, and this could happen here too,” she says.

Gumleaf skeletoniser is also an urban problem because it is hazardous to people. The long hairs of the caterpillar inject venom into human skin on contact, which can cause a painful skin irritation.

Auckland Council’s Manager of Parks, Sport and Recreation Ian Maxwell says this pest has impacted trees across Auckland for ten years.

“Trees that provide shade and have become part of the Auckland landscape have suffered and died. Until now we have relied on expensive treatments such as injecting trees and the removal of infested foliage. At best this has proved a stop gap measure. We are hopeful that biological control will help manage this pest,” Mr Maxwell says.

Biological control has been a very effective and safe means of managing other eucalypt pests in New Zealand. When successful, it provides a sustainable alternative to applying chemical insecticides.

Scion has been working on biological control since 2007 to help manage gumleaf skeletoniser, as part of a Ministry of Agriculture and Forestry (MAF) Sustainable Farming Fund project.

The most suitable biological control agent was found to be the Australian parasitic wasp Cotesia urabae.

This wasp was chosen because it specifically targets the gumleaf skeletoniser caterpillar, laying its eggs inside the caterpillar’s body.

It was sourced from Tasmania, with the help of Dr Geoff Allen (University of Tasmania/Tasmanian Institute of Agricultural Research), so is adapted to a climate similar to New Zealand.

“The wasp is so tiny, most people will never see it,” Dr Berndt explains.

“Our research has shown that the wasp poses no significant risk to native insects in New Zealand, and has no known effects on humans.”

“It certainly won’t sting people as other wasps do,” she adds.

Following the first release today of Cotesia urabae, Scion will continue to distribute the wasp over the coming months and years.

The success of the release and ongoing impacts will be closely monitored.

The Environmental Risk Management Authority (ERMA) granted permission for the wasp’s release into New Zealand following three years of research by Scion and consultation with a wide range of industry and community groups.

Given the potential negative effects of the gumleaf skeletoniser caterpillar, ERMA concluded that the benefits of releasing the wasp outweighed any possible risks.

The release event held at the Auckland Domain today was attended by representatives of the forestry sector, Auckland Council, Environment Waikato, Bay of Plenty Regional Council and other interested parties.