Farm Forestry New ZealandDecember, 2016
Update on Paropsis biocontrol December 2016
The parasitoid wasp Eadya paropsidis remains a strong candidate for safe release as a biological control agent for Eucalyptus tortoise beetle in New Zealand.
Eadya paropsidis has been identified as the most promising biocontrol agent for Eucalyptus tortoise beetle (Paropsis charybdis) which feeds on the foliage of many eucalypt species, including those that form an important and growing part of New Zealand’s diversified forest estate. Plantation Eucalyptus nitens cover ~14,000 ha and contribute ~$40 million pa in hardwood chip exports as well as increasingly contributing to sawn wood products.
Both parasitoid wasp and beetle are native to Tasmania. Field work in Tasmania has found not one, but five different species of Eadya. The different species were found to parasitise different eucalypt leaf-feeding paropsine beetles. The species reared from P. charybdis and P. agricola is the species that has been imported by Scion for further research. In the interim it will continue to be called E. paropsidis but a new description and name is expected to be published eventually.
Other work undertaken by our University of Tasmania collaborators has also yielded some important insights into rearing the parasitoids in the laboratory. Eadya parasitoids were most likely to survive to pupation if their beetle larva hosts were large at prepupation. Post-pupation survival improved for pupae that lost less than 50% of their body weight in the first month after pupation. Emergence and flight of the new wasps in nature was influenced by temperature (optimal 19 - 23?C) and wind speed (not over 23 km/h). In Tasmania in 2015, the peak for Eadya paropsidis flight was 24 November.
The effect of nutrition and body size of host beetle larvae on successful rearing of the Eadya parasitoids comes just in time. Mass-rearing of Eadya parasitoids on paropsis in containment in Rotorua was relatively unsatisfactory for the second season in a row. Eadya larvae emerged from only 43% of the successfully parasitised Paropsis larvae. Successful mass-rearing in the laboratory is essential for achieving successful biological control for New Zealand and work will continue in this area.
Host Specificity Testing
Host specificity testing is another focus of the entomologists at Scion. Before recommending release of Eadya as a biological control agent, it is necessary to make that it does not attack the larvae of native or beneficial beetles. The results for the species tested to date are summarised in the table below.
| Non-target beetle | Evidence of attempted parasitism (%) | No-choice observation | Two-choice observation | Comment and Conclusion |
| Acacia pest beetle Dicranosterna semipunctata | 3, no parasitoids emerged | 1 attack out of 10 | Still to do | Unlikely host |
| Tutsan leaf beetle Chrysolina abchasica | 3, no parasitoids emerged | 2 attacks out of 15 | Unlikely host | 3 attacks out 16 |
| Broom leaf beetle Gonioctena olivacea | 36; no parasitoids emerged | 1 attack out of 13 | No attacks |
Larvae smaller than smallest paropsine host. |
| Heather beetle Lochmaea suturalis | No parasitism | 1 attack out of 12 | No attacks | Larvae smaller than smallest paropsine host. Not a host |
The results are very promising so far as experts in insect behaviour would expect to see some parasitoids trying to attack closely related non-target beetle species, especially when presented with no other choices within the artificial confines of small petri dishes within a laboratory. More importantly, no Eadya paropsidis emerged from any non-target beetle larvae (whereas Eadya parasitoids did emerge from 45% of attacked P. charybdis larvae).
Further host specificity testing on more non-target beetles is the plan for this summer. In particular, a significant effort needs to be made to search for and learn more about the sub-alpine native beetles within the Chrysomelinae, Chalcolampra speculifera and Allocharis sp. Catching and rearing these rare beetles to assess them for non-target risk may prove challenging. When host specificity testing is complete, Maori, community and interest groups will be engaged and, an application to release the parasitoid from containment will be submitted to the Environmental Protection Authority in 2018.
Funding
This project builds on the previous SFF study “Scoping potential Biological Control for Eucalyptus Tortoise Beetle larvae” (12/039). MPI has supported this project again by funding the current SFF grant, which is led by the NZ Farm Forestry Association and co-funded by South Wood Exports Ltd, Oji Fibre Solutions NZ Ltd., Scion MBIE Core funding and the Speciality Wood Products Partnership. Timberlands Ltd and Ernslaw One also contribute to the project team.
For more information, contact Toni Withers at Scion, toni.withers@scionresearch.com
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