Locating a biological control for tutsan in New Zealand

Overview

Results

The team

Related information

So what's the problem?

Tutsan, Hypericum androsaemum L., is an evergreen or semi-evergreen shrub of the family Cluciaceae (or alternatively Guttiferae). It grows up to 1.5 m high. In New Zealand, tutsan has become a common weed in higher rainfall areas, growing in open forest, forest margins, scrub, waste places and garden surroundings. It is shade tolerant, unpalatable to livestock and tends to infest areas in which mechanical and/or chemical control options are impractical.

What is this project doing?

In 2009, a report was prepared by Landcare Research for the Tutsan Action Group to evaluate the prospects for biological control of tutsan by reviewing the literature to identify potential biocontrol agents, assessing the prospects of achieving successful control and estimating the costs of such a programme.

Results revealed only few arthropod and fungal pathogen species that attack tutsan in its native range, most with too broad a host range (attacks many different species) to be considered for biological control. This may be because the arthropod and fungal pathogen community has not been explored properly. Tutsan is also a weed in Australia (Victoria). A biocontrol programme in the state of Victoria was abandoned at an early stage when a rust fungus, Melampsora hypericorum, was found to have self-introduced. Although the amount of damage inflicted by the rust is variable, the plant is generally well controlled at sites where the rust is prevalent. Although the rust is also present in New Zealand, it is not successfully controlling tutsan. It was shown that different populations of the weed vary in their susceptibility to the different strains of the rust. Therefore, a search was proposed for more virulent strains of the rust in Europe, where it originates. Since rusts are often genotype specific, it will be necessary to determine where exactly the tutsan in New Zealand originates in order to concentrate sampling efforts on different rust strains of this region.

In 2011, CABI’s centre in Switzerland was approached by Landcare Research New Zealand to conduct field surveys in the area of origin of tutsan to:

collect leaf samples from tutsan for molecular analyses
collect rust samples for molecular analyses
survey tutsan for phytophagous arthropods and other fungal pathogens
evaluate their potential as biological control agent

Results so far

In spring 2012, MSc student, Elena Olsen, was engaged on the project. Elena is enlisted at the University of Fribourg in Switzerland, where she will be supervised by Prof. Heinz Müller-Schärer. First surveys in the UK and Ireland took place in May 2012. About 28 tutsan sites were found, however, many had only very few (less than 10) plants. Plant samples for molecular analyses were taken at all sites, while quantitative field sampling was conducted at six sites. This included recording the approximate population size, the density of tutsan, its cover, individual plant parameters, insect and fungal damage and quantitative samples of insect herbivores. Rust infection was present at approximately a third of the sites. Other possible signs of pathogen infection found included leaf spots, leaf necrosis and stunted shoot growth. Herbivores with possible potential for biological control included a seed feeding bug and a tortricid moth species.

In June, a second field survey took place in France and northern Spain where plant samples were collected at a total of 16 sites and quantitative field sampling was conducted at three sites. Tutsan appeared to be fairly common along roadsides and in open forests in the Basque region of Spain and France, but far less abundant in the rest of France. The rust was present at about half of the sites, but appeared to be less prominent than in the UK and Ireland, which might have been due to the timing of sampling. In Spain, at least one chrysomelid beetle species was collected from four sites and larval feeding damage was found at an additional two sites. Other new herbivores found included a stem-boring moth, a leaf-miner, a katydid species and a phasmid. All insects of potential interest for biocontrol will be sent to taxonomists for identification. An additional survey is being planned in the northern UK in August.

Sampling will be continued in 2013 and will depend on results obtained in 2012.

Project Executive