Results of the first year of a Sustainable Farming Fund study to locate a spring-active parasitoid in Tasmania
for potential biological control of Paropsis charybdisAugust, 2013.
Despite considerable efforts, the eucalyptus tortoise beetle Paropsis charybdis continues to defoliate Eucalyptus nitens plantations throughout New Zealand. This pest both prevents expansion of this forest resource and requires constant management through aerial insecticide application.
Toni Withers, Geoff Allen, Dean Satchell, Hannah Fluitsma, Martin Bader
Scion & Tasmanian Institute of Agriculture
BACKGROUND AND SUMMARY
In 2012/13 the NZ farm Forestry Association led a Sustainable Farming Fund (SFF) research project named Contract 12-039 “Scoping Biological Control for Eucalyptus Tortoise Beetle Larvae”. This report summarises the 2012 Fieldwork conducted in Tasmania by the project team.
A parasitoid wasp of the spring-time larval stage of the eucalyptus leaf beetle Paropsisterna agricola in Tasmania is being studied as a potential biological control agent for New Zealand. The potential agent Eadya paropsidis 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.
Both sequential no-choice and two-choice testing methods examined the response of individual field-caught wasp females towards P. agricola (a paropsine pest of E. nitens in Tasmania but not present in New Zealand) or P. charybdis larvae or both (a two choice method). Females behaved significantly more positively in attacking P. agricola larvae than in attacking P. charybdis larvae, but both species were attacked and wasps reared out from them. However, this preference for attacking P. agricola may just be a result of the prior field experience they had unavoidably had.
Sentinel larval field trials involve placing laboratory reared host larvae in the field, in the natural environment where the parasitoid is found, to assess levels of parasitism. These were conducted by seeding groups of laboratory reared P. charybdis larvae out into E. nitens foliage in five separate locations in Tasmania, as well as field collections made of wild P. charybdis larvae. Reared from these collections were larvae of natural enemies including both Tachinid flies and E. paropsidis specimens, some of which have been sent overseas for identification, while the remaining have been placed into over-wintering conditions in the laboratory. The results suggest this spring-active parasitoid E. paropsidis has good potential as a biological control agent for P. charybdis in New Zealand. This potential agent will be further evaluated in year 2 of the SFF study.
BACKGROUND - PAROPSIS IN NEW ZEALAND
Paropsine beetles (of which eucalyptus tortoise beetle is one species) are extremely diverse and abundant in their native Australian range but they 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 charybdis has effectively prevented the commercial establishment of the highly favoured pulp species Eucalyptus nitens until the introduction of the egg parasitoid Enoggera nassaui.
Paropsis charybdis 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. After appearing in November E. nassaui can control the latter portion of first generation eggs. The second generation of eggs laid in summer time 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 effective.
With the market projections for sustainably grown E. nitens continuing to increase we undertook a fresh look at biological control prospects available to us for targeting the first generation of P. charybdis. The braconid wasp Eadya paropsidis, was the obvious first choice for consideration, it produces one generation per year and is responsible for high percentages of first generation parasitism of Paropsisterna agricola in E. nitens plantations in Tasmania. Our first priority was to establish whether E. paropsidis would be effective against P. charybdis and be physiologically compatible.
A preliminary study undertaken in 2011 confirmed that P. charybdis was indeed a highly suitable physiological host for E. paropsidis. Additional research is now being undertaken under a SFF research project - namely Contract 12-039 “Scoping Biological Control for Eucalyptus Tortoise Beetle Larvae”. This report summarises the outcome of the first year of research undertaken by the project team and also under sub-contract to entomologists at the University of Tasmania (TIA) in 2012-13.
THE SFF PROJECT 2012
The first year of the SFF project “Scoping Biological Control for Eucalyptus Tortoise Beetle Larvae” has been a great success. We were able to carry out a number of laboratory experiments and sentinel larval trials in the field. The laboratory experiments have revealed that field-caught female E. paropsidis (the spring-active natural enemy we are most interested in) readily attacks P. charybdis in the laboratory.
Attacked P. charybdis larvae reared right through showed similar infestation levels from E. paropsidis to the P. agricola larvae in the laboratory experiments. If this parasitoid wasp were introduced into New Zealand it is likely that if the rearing host was P. charybdis and field experience was limited to infestations of P. charybdis, that female E. paropsidis search and attack behaviour would not be a limiting factor to biological control success.
The careful field searches conducted by Dean Satchell in December 2012 resulted in additional information. He observed that wild populations of P. charybdis in Tasmania are being readily attacked by E. paropsidis. This is very encouraging to the potential biological control project. Adding weight to this was the results of the sentinel larval trials, in which E. paropsidis infested a higher proportion of most larvae that had only been exposed to them in the field for 72 hours than did Tachinid flies in three out of four sites (Tachinidae are another common natural enemy of paropsine larvae in Tasmania). In fact E. paropsidis was found to be active in every site except for one in which we located wild populations or undertook sentinel larval trials with P. charybdis in December 2012.
The second year of planned research under this SFF-funded project will answer many more of the important questions that arise from this study, including confirming parasitoid identity, and establishing laboratory rearing methods.
More details of the trials and experiments, along with methods and results, can be found in the full report prepared by Scion.