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Gumleaf skeletoniser: Potential for biological control

From Biosecurity 69, August 2006.

The recent discovery of gumleaf skeletoniser (Uraba lugens) in Katikati, Bay of Plenty, marks a southward movement of the tree pest out of the Auckland region. The pest has also been intercepted in a pheromone trap near Warkworth, Northland, confirming that gumleaf skeletoniser is on the move in both directions.

Without intervention, the spread of this Australian insect pest, which targets a large number of Eucalyptus species, could have long-term implications, mainly for hardwood growers, due to loss of productivity caused by defoliation. This increases the pressure to find long-term management options, including biological control.

Biosecurity New Zealand (BNZ) has funded the establishment of a biological control programme that offers considerable promise for helping to manage gumleaf skeletoniser in this country. BNZ support has enabled Ensis scientists to identify and import potential biological control agents from Tasmania and South Australia for further testing.

Two potential control agents

The white cocoons next to these dead caterpillars belong to the parasitoid Dolichogenidea eucalypti, a species that attacks gumleaf skeletoniser in Australia. This species is one of a few that may prove useful as biological control agents in New Zealand.

Ensis entomologists have narrowed the potential agents down to two parasitic wasps: Cotesia urabae and Dolichogenidea eucalypti. Both wasps are only known to attack gumleaf skeletoniser caterpillars. They lay their eggs inside the host caterpillar and the parasitic larva eventually emerges, killing its host.

Just as gumleaf skeletoniser has made itself at home in New Zealand, so both of the short-listed enemies are also expected to thrive. The challenge is to rear these wasps in quarantine in sufficient quantities so that host testing can be carried out. Host testing is needed to find out if the wasps will attack any beneficial or native species.

Life in a goldfish bowl

Ensis entomologist Dr Lisa Berndt says that over the past year-and-a-half scientists have wrestled with getting to know the insects and encouraging them to mate in quarantine. “This is no small task for these species, whose libido drops the minute they are placed in a jar!”

Lisa explains that biological control demands a great deal of careful research. However, once a suitable agent is identified and released, ongoing control is self sustaining.

“When it is successful, biological control offers a sustainable alternative to chemical control and is often the most desirable long-term management solution. Within the forestry sector, nine of the 12 insect pests that have been targets of biological control have succumbed to complete or substantial control.”

Eucalypt pests successfully controlled using this technique include the gum tree scale (Eriococcus coriaceus), the gum tree weevil (Gonipterus scutellatus), and the leaf blister sawfly (Phylacteophaga froggatti).

Lisa Berndt, Ensis



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