International weed biocontrol symposium

In late August, 203 weed biocontrol experts, representing 100 organisations from 25 countries, attended the 15th International Symposium on Biological Control of Weeds (ISBCW) at Engelberg in Switzerland. The first-ever ISBCW was held in Switzerland in 1969, and over the years this event has become the key forum for refining international best practice and developing new collaborations for weed biocontrol. Since classical weed biocontrol projects always involve an overseas component of work, such international collaboration is critical for every project, and this discipline is renowned for the generosity with which information and resources are shared willingly.

Participants at IBSCW2018. Image: CABI

Europe has for many decades helped other parts of the world to develop biocontrol for weeds of European origin but is only just beginning to have the processes and support for the development of biocontrol for its own weeds. Agents have recently been released in Europe to attack Japanese knotweed (Fallopia japonica), Himalayan balsam (Impatiens glandulifera), and Sydney golden wattle (Acacia longifolia), and it is hoped other agents can be released against further targets soon. Further support for biocontrol in Europe will hopefully be boosted as people become aware of the benefits. A leaf beetle (Ophraelia communa), recently self-introduced to Europe, will hopefully help with this. The beetle is providing useful control of ragweed (Ambrosia artemisiifolia), leading to a substantial reduction in hay fever and other allergic symptoms experienced by many people in Europe. Ragweed pollen is down 85% since the beetle established.

Despite the strong history of international collaboration, the international weed biocontrol community has struggled since the Nagoya Protocol came into force in 2014. This is a supplementary agreement to the Convention on Biological Diversity aimed at the fair and equitable sharing of benefits arising from the utilisation of genetic resources. There were several presentations, lots of discussions, and a workshop on this topic. Each country that is a party to the agreement (currently 104) needs to figure out how it will implement the protocol. Many are not restricting access to genetic resources such as biocontrol agents, but others are, and it is taking some time to clarify the requirements and best-practice processes that will once again allow biocontrol agents to be freely shared. However, it is looking more hopeful that this situation is starting to improve. Key groups will continue to lobby for classical biocontrol agents to be treated as a special case since they are used for public good rather than commercial enterprise.

Although New Zealand is a small country, with a modest budget for weed biocontrol, it continues to more than hold its own on the international stage. Supportive legislation and stakeholders, relatively stable funding, and the dedication of a passionate group of researchers has seen New Zealand continue to steadily release new agents where other countries have struggled or stalled. The Kiwi team presented seven oral papers and six posters, as follows.

Quentin Paynter gave a keynote address summarising insights arising from underpinning research undertaken in New Zealand, which has helped to both refine best practice and cut the costs of developing biocontrol programmes. This includes robust data-driven processes for choosing the best targets, and minimising wastage, through avoiding agents that are likely to be parasitised or subjected to heavy predation, or rejected unnecessarily because of non-target feeding damage which is simply an artefact of cage/indoor testing. Quentin also prepared a poster on the substantial achievements of the Cook Islands project (see Great results in the Cook Islands this issue).
Lynley Hayes, and collaborator Michael Day from Australia, spoke about weed biocontrol efforts in Vanuatu and outlined the new project now underway to develop further weed biocontrol programmes there (covered in Issue 85).
Simon Fowler shared recent studies on the economics of biocontrol for St John’s wort (Hypericum perforatum), ragwort (Jacobaea vulgaris), mist flower (Ageratina riparia), and alligator weed (Alternanthera philoxeroides) (all covered in previous issues). A key message was that even if you don’t have a lot of data to work with, which is often the case, you can still do a surprising amount with it. He revealed that the $3 million invested in the four programmes evaluated to date delivers an astonishing $67 million in benefits to New Zealand annually.
Ronny Groenteman outlined the new project to developing biocontrol for horehound (Marrubium vulgare), and the approach taken for handling the vigorous opposition from medical herbalists, which potentially could have derailed the project. Soon after ISBCW we heard that the Environmental Protection Authority had approved the release of the horehound moths (more on this in the next issue).
Lindsay Smith presented a poster on pre-release screening of weed biocontrol agents for pathogens, which became mandatory in New Zealand in 1984 but (incredibly) is still not a requirement in other parts of the world. Subsequent follow-up of agents released here pre-screening has fortunately not found any evidence that diseased agents were released (covered in Issue 73).
Hugh Gourlay prepared two posters. The first outlined the challenges involved in attempting to develop an artificial diet for the Japanese honeysuckle stem beetle (Oberea shirahatai). This beetle can take up to 2 years to complete its life cycle, and it was hoped that an extra nutritious diet could help to speed that up, providing more beetles for release more quickly. However, it has proven too difficult to reliably produce beetles without deformations when using this approach. The second poster summarised the project to develop biocontrol agents for tutsan (Hypericum androsaemum), which has recently resulted in the release of a beetle (Chrysolina abchasica) and a moth (Lathronympha strigana) (covered in Issue 80).
Hester Williams, who is undertaking a PhD at Auckland University but is located with the team at Lincoln, presented results from her study looking at the influence of low-density populations and Allee effects on biocontrol agents. Using the tradescantia leaf beetle (Neolema ogloblini) as a study organism, Hester found that establishment was better when larger numbers of beetles were released, and that predation may play a significant role in this.
Graeme Bourdôt, of AgResearch, spoke about a joint project between AgResearch and Manaaki Whenua – Landcare Research, which found that, when the costs and benefits of biocontrol for nassella tussock (Nassella trichotoma) were modelled, this project appeared highly worthwhile (covered in Issue 81). This has resulted in a funding application to progress this work being submitted in August.
Mike Cripps, of AgResearch, prepared a poster on the impact of the green thistle beetle (Cassida rubiginosa) on Californian thistle (Cirsium arvense) in New Zealand, which found that once densities of ≥10 larvae per shoot are achieved this beetle provides useful control (see How effective is the green thistle beetle? this issue).
Dilani Hettiarachchi, of Lincoln University, shared results from her PhD study in which she has looked at the importance of plant volatiles in host-plant selection by female green thistle beetles (Cassida rubiginosa). This beetle attacks a range of thistles in the Cardueae tribe, and this study found that as phylogenetic distance from the primary host (Cirsium arvense) increases, the beetles’ preference for alternative hosts decreases for all factors tested: olfactory choice, feeding and oviposition preference.
Seona Casonato, of Lincoln University, shared the findings of a student project she co-supervised, which compared two isolates of a fungus (Sclerotinia sclerotiorum). This fungus has been explored by AgResearch for a number of years as a potential bioherbicide for Californian thistle (Cirsium arvense), but challenges around ensuring reliable efficacy remain to be resolved. This study concluded that the two isolates could potentially be used together to overcome differences in the susceptibility of different genotypes of Californian thistle.

Other items from ISBCW of interest included the following.

The possibility of using gene drives to control weeds (see Could gene drives be used to control weeds? this issue).
A programme to develop biocontrol for yellow flag iris (Iris pseudacorus) has recently been initiated for South Africa, with the assistance of Belgian collaborators. Surveys in Belgium and Italy have uncovered two promising natural enemies, which are now being tested to determine their suitability: the iris flea beetle (Apthona nonstriata) and a flower-feeding weevil (Mononychus punctumalbum).
Follow-up evaluation of a programme against parrot’s feather (Myriphyllum aquaticum) in South Africa, a decade after the release of a leaf-feeding beetle (Lysanthia sp.), has found impressive results. The weed is now absent from most of the 56 sites monitored and is still weedy at only two.
Further agents will be sought for woolly nightshade (Solanum mauritianum) in South Africa, as the lace bug (Gargaphia decoris) and the flowerbud weevil (Anthonomus santacruzi) seem unlikely to exert sufficient control alone. This is a good opportunity for further collaboration on this target between South Africa and New Zealand.
A study in Australia has found that observed severe dieback of blackberry (Rubus fruticosus agg.) there is associated with Phytophtora species. However, testing has shown that these pathogens are not sufficiently host-specific to use for biocontrol purposes.
Follow-up evaluation of the impact of the white smut (Entyloma ageratinae) on mist flower(Ageratina riparia) in Australia has, like in New Zealand, found a major reduction in the weed with a corresponding benefit to native plant species richness and abundance.
A workshop was held on biocontrol for grasses. Grasses were previously believed to be too difficult to target with this approach, but with recent work on projects such as giant reed (Arundo donax) showing what is possible, there is now increasing interest in targeting more grasses.
The world catalogue, which has information about all weed biocontrol agents released so far, will be updated soon. It is available online at www.ibiocontrol.org. All ISBCW proceedings are also available on this website.