PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND
Dean Satchell heads to Tasmania to assist with mass-rearing Eadya paropsidis, the potential biological control agent of Paropsis charybdisDecember, 2013.
Despite considerable efforts, the eucalyptus tortoise beetle Paropsis charybdis (paropsis) continues to defoliate Eucalyptus nitens plantations throughout New Zealand. The pest both prevents expansion of this forest resource and requires constant management through aerial insecticide application. The NZ Farm Forestry Association and partners are undertaking a Sustainable Farming Fund (SFF) research project, “Scoping Biological Control for Eucalyptus Tortoise Beetle Larvae” to investigate effective biological control of this pest.
Toni Withers, Geoff Allen, Dean Satchell
Scion & Tasmanian Institute of Agriculture
Eadya paropsidis, a parasitoid wasp of the spring-time larvae of the eucalyptus leaf beetle Paropsisterna agricola in Tasmania, is being studied as a potential biological control agent for New Zealand. The wasp was caught as adults on the wing from E. nitens plantations in northern Tasmania in December 2012, and brought into the laboratory in Hobart for behavioural testing.
During the first year of research, the behaviour of these field-caught females towards P. agricola (a paropsine pest of E. nitens in Tasmania but not present in New Zealand) compared to P. charybdis larvae, was examined. Females preferred to attack P. agricola larvae they were most familiar with, but also attacked P. charybdis larvae. Their preference for attacking P. agricola larvae is probably a result of the prior field experience.
Field collections have shown that paropsis larvae are readily attacked by E. paropsidis and the identity of the parasitoid wasps has been verified by an international expert. Molecular identifications have revealed that at one site, the genetic profile of E. paropsidis reared from E. paropsidis and paropsis, are identical. This supports laboratory findings that female wasps in Tasmania can attack the larvae of a number of paropsine leaf beetle species if they are present in spring when they are active. Additional molecular research is underway.
THE SFF PROJECT 2014
Although the first year of “Scoping Biological Control for Eucalyptus Tortoise Beetle Larvae” was successful at confirming attack of paropsis by E. paropsidis in both the laboratory and in multiple field sites, sadly laboratory rearing of the parasitoid offspring was less so. Many wasp larvae, which emerge from the dead remains of the beetle larva they have just consumed, failed to spin their own cocoons in many of the conditions we provided. This summer, Dean Satchell will again travel to Hobart and assist the University of Tasmania contractors with the project.
Dean will help feed numerous hungry, leaf-munching larvae while the parasitoids develop inside them. Emerging parasitoid larvae will then be sandwiched within their own mesh “Christmas stocking” to assist the process of spinning. It is hoped this second year of research will provide sufficient E. paropsidis pupae to enable a successful importation into Containment in New Zealand in 2014.
BACKGROUND - PAROPSIS IN NEW ZEALAND
Paropsine beetles (of which eucalyptus tortoise beetle is one species) are diverse and abundant in their native Australian range, and rarely cause substantial damage in natural and undisturbed forest. They have emerged as significant eucalypt defoliators only since the expansion of managed plantation forestry, particularly when host trees are planted outside their native range. In New Zealand since 1916, paropsis has effectively prevented the commercial establishment of the highly favoured pulp species Eucalyptus nitens until the introduction of the egg parasitoid, Enoggera nassaui.
Paropsis completes two generations per year in New Zealand. The first generation of eggs are laid in spring from October onwards, and those laid early often escape any natural enemies. E. nassaui appear in November and can control the latter portion of first generation eggs. The second generation of eggs, laid in summer, are effectively controlled by E. nassaui as well as by a self-introduced primary egg parasitoid (Neopolycystus insectifurax) which was first found here in 2000.
Biological control of eucalyptus leaf beetle has been disrupted by the arrival of the hyperparasitoid of E. nassaui, Baeoanusia albifunicle. Since its self-introduction around 2000, parasitism of the spring generation of P. charybdis has not been as effective.
With market projections for sustainably grown E. nitens continuing to increase, we undertook a fresh look at biological control prospects for targeting the first generation of paropsis. The braconid wasp, Eadya paropsidis, was the obvious choice for consideration; it produces one generation per year and is responsible for high percentages of first generation larval parasitism of Paropsisterna agricola in E. nitens plantations in Tasmania. Our first priority was to establish whether E. paropsidis would be effective against paropsis and be physiologically compatible, both of which have now been confirmed. Research undertaken to date within the SFF research project - namely Contract 12-039 “Scoping Biological Control for Eucalyptus Tortoise Beetle Larvae” – can be read in the summary of the first year of research.