Old man’s beard to face new attack
Old man’s beard, showing stunting caused by a leaf- and bud- galling mite after 60 days
Entomologist Lindsay Smith is visiting Serbia in May to look for some small but hopefully ‘mighty’ biocontrol agents that might be able to finally give old man’s beard (Clematis vitalba) a much-needed trim. This highly invasive vine smothers native trees and sub-canopy plants, preventing regeneration and modifying the natural interactions necessary for a healthy forest ecosystem. “Although it has no beneficial environmental or economic attributes, old man’s beard has been a difficult biocontrol target because of the need to avoid harming our native Clematis species,” explained Lindsay.
Attempts to introduce biocontrol agents in the 1990s have been less than successful, for a variety of reasons. Initial damage from a fungal disease (Phoma clematidina) looked promising, but the disease died out. A leaf-mining fly (Phytomyza vitalbae) established well, but it is being attacked by its own natural enemies and so is not putting enough pressure on the plants to significantly stunt their growth. A sawfly (Monophadnus spinolae) was also introduced, but despite being released at a number of sites around New Zealand, it has only been detected in low numbers at one site near Nelson. “We don’t fully understand why the sawfly didn’t establish well,” said Lindsay. It was a difficult insect to rear and, with hindsight, the material released may have been significantly genetically bottlenecked.”
“We are facing an uphill battle with this plant and it remains a serious threat, so we aren’t giving up just yet,” said Lindsay. “We recently ruled out a beetle (Xylocleptes bispinus), which kills whole vines because it posed too great a risk to native Clematis. However, we are planning to have another go at establishing the sawfly, which can cause substantial defoliation when present in large numbers,” he added. The sawfly will be re-released, in much bigger numbers and with better genetic diversity, at a site carefully chosen to be as be safe as possible from disturbance. “We will also take steps to ensure that wasps don’t impact on the newly released sawflies, although we don’t think that is a key reason for the poor establishment previously, since the larvae readily ooze haemolymph when threatened, which deters predators,” he explained. The sawfly population in Serbia may also have a better climate match with New Zealand than earlier introductions, allowing it to do better.
Another option currently being pursued is a leaf- and budgalling mite (Aceria vitalbae), which damages and stunts growing tips. Host range testing of this tiny mite has recently been completed by Dr Biljana Vidovic from the University of Belgrade. “Eriophyid mites typically have a very narrow host range, and this one proved no exception,” explained Lindsay. Fourteen species or hybrids of Clematis were sent to Serbia, and galls with viable mite populations only developed on old man’s beard. “We are now at a point where we can apply to the Environmental Protection Authority for permission to release the mites,” said Lindsay.
Horizons Regional Council will be the applicant on behalf of the National Biocontrol Collective. The application process involves consulting with iwi and a large range of organisations. The application discusses some of the potential implications for existing food-webs that occur in New Zealand. “One of the scenarios we look at is what might happen if the new mite species builds in number, creating an abundant food source for predatory mites, which then build in number, with downstream effects on other prey species,” said Richard Hill, who is preparing the application. “In this case, we know that the leaf- and bud-galling mite forms galls on old man’s beard, which offer a great deal of protection from predators, so we don’t expect them to become a major new food source for predators,” he said. A summary of the results from host range testing conducted in Serbia as well as responses following consultation with relevant organisations will be included in the application and made available to the public.
Lindsay will be attempting to return from Serbia with good numbers of both the sawflies and the mites, which will go straight into the containment facility at Lincoln until they can be released. “Previous experience has shown that there is a very narrow window of opportunity to collect the sawflies and it is easy to miss it! So I am leaving with plenty of time up my sleeve in the hope that I will return home with some very welcome new tools with which to battle old man’s beard,” he said.
This project is funded by the National Biocontrol Collective. For more information about the leaf- and bud-galling mite EPA application, see: www.landcareresearch.co.nz/science/plantsanimals-fungi/plants/weeds/biocontrol/approvals/currentapplications/old-mans-beard.
CONTACT
Lindsay Smith – smithl@landcareresearch.co.nz