Final Phase for Tutsan Project
After more than a decade of research and enthusiastic volunteer input, the tutsan project is now reaching its final phase. “This project has produced several new science discoveries and has been of considerable interest to both farmers and other researchers around the world,” said Hugh Gourlay, who has led the project. “Much of the success of this project has been due to the strong collaboration between the Tutsan Action Group (TAG) and their communities. This helped to secure the necessary co-funding and co-operation from farmers and land managers,” said Hugh.
Tutsan Moth
It all started in 2007 with a group of farmers who were concerned about the growing problem with tutsan (Hypericum androsaemum) in the central North Island, which led to the formation of the TAG. Their first key milestone was gaining funding from the Sustainable Farming Fund (SFF) to support a study into whether biocontrol of tutsan might be feasible. This study found that surveys of the plant in the native range were needed, since the natural enemies of tutsan were generally not well known. The TAG then successfully applied to SFF for funds to do these surveys, and CABI-Switzerland got this work underway in Europe in 2010. Research undertaken by MSc student Elena Olsen suggested that the centre of origin for tutsan in Europe is Georgia, in the Caucasus. This meant that surveys in Georgia were especially important, since the centre of origin is where the richest diversity of natural enemies can be expected, in addition to surveying other parts of Europe where tutsan is common.
One natural enemy of tutsan was well known, having been present in New Zealand since the 1950s. Tutsan rust (Melampsora hypericorum) appears to be controlling tutsan in the South Island, where the plant is not invasive, but not in the North Island. Molecular studies have shown that there are two main strains of the rust present in New Zealand, with one type in the South Island and the other in the North Island. (Stewart Island has both.) Also, four genotypes of tutsan are present in New Zealand, although two of these are rare (see map). The two common genotypes, like the rust, are mainly divided between the North and South Islands. In Europe eight tutsan genotypes were found and four rust genotypes, including the two found here. “Testing was undertaken to see if the two new rust genotypes identified might be useful, but unfortunately the North Island tutsan genotype was found to be resistant to all of the rust strains found in Europe,” explained Hugh. This helps to explain why tutsan is problematic in the North Island but not in the South.
The surveys also looked for insects, and two with good potential were found. The larvae of the tutsan moth (Lathronympha strigana) feed on shoot tips and inside stems, reducing plant growth. The larvae also feed inside the fruits, destroying the seeds. Both the adults and larvae of the tutsan beetle (Chrysolina abchasica) feed on the leaves and can strip the foliage. A third successful SFF application by the TAG allowed these insects to be host-range tested and approved for release in New Zealand, followed by mass-rearing and the first field releases of both in 2017.
“We have had some issues with a microsporidian disease appearing in our tutsan moth- rearing colony. It was a bit perplexing as routine testing (including molecular tests) after shipments of the moths were imported would show that moths were disease- free, but later, when testing was done prior to gaining permission to release them from containment, the disease would be found”, said Hugh. After further investigation we now believe that the disease is most likely being introduced to the moths post-border rather than the moths bringing it with them undetected. Native and unwanted pest leafrollers, which do commonly frequent tutsan, have microsporidian diseases and it seems likely that the tutsan moths are catching the disease when fed foliage grown outdoors. Such diseases have been poorly studied, and more work is needed to confirm this. Also, time will tell whether the establishment success and effectiveness of the moth, which has now been released widely in the central North Island, will be affected. However, leafrollers commonly reach pest populations despite have microsporidian diseases, and so the impact on the tutsan moth may not be significant.
The tutsan beetle proved quite difficult to rear. This beetle is unusual in that adult females usually produce larvae directly rather than eggs. However, eventually enough beetles were produced to make releases at about a dozen sites. The beetle is closely related to the highly successful St John’s wort beetles (Chrysolina spp.), and it is hoped they will be able to deliver a similar result.
While the final SFF project is now officially drawing to a close, the work will not end there. Monitoring of the establishment success of the tutsan agents will continue with the help of TAG members, and there will be some work required to help spread them around to all areas where they are needed. Manaaki Whenua – Landcare Research will also be continuing to undertake some field experiments with the tutsan beetle. In laboratory host-range tests the beetles were able to utilise two native Hypericum species. However, they did poorly on these native plants and the evidence overwhelmingly suggests that the beetles will not attack them in the field (i.e. it is a lab-testing artefact). However, as per current best practice, where there is any potential for non-target attack this is always closely followed up.
A huge thanks to the members of the Tutsan Action Group for their efforts, and to the organisations who supported them. Thanks also to the Ministry for Primary Industries for awarding the three Sustainable Farming Fund grants that made this project possible. Follow-up work on the field host range of the tutsan beetle and origins of the microsporidia in tutsan moth is being funded by the Ministry of Business, Innovation and Employment as part of Manaaki Whenua – Landcare Research’s Beating Weeds programme.
CONTACT
Hugh Gourlay – gourlayh@landcareresearch.co.nz
or from May until September
Arnaud Cartier – cartiera@landcareresearch.co.nz