Darwin’s Barberry Focus Shifts to Disease
Darwin’s barberry (Berberis darwinii) has the potential to become a serious woody weed like gorse (Ulex europaeus) and broom (Cytisus scoparius) in New Zealand.
Biocontrol efforts have until recently focused on finding insect agents for this weed. Our Chilean collaborator, Hernan Norambuena, has been helping out with the project for several years. He completed the host-range testing of a seed-feeding weevil (Berberidicola exaratus) and a flowerbud weevil (Anthonomus kuscheli) which the Environmental Protection Agency (EPA) subsequently approved for release in New Zealand. More recently he has been helping with a rearing programme to enable releases of the weevils to begin. All insect shipments arriving from overseas must be reared through a generation in a containment facility to check their identity and ensure there are no unwanted hitchhikers. Only then can we apply to the Ministry of Primary Industries for permission to remove the insects from containment and liberate them in the field. With Hernan’s help we have now imported several shipments of the weevils, but it has proved more difficult than expected to successfully rear them in containment.
Our first attempt at rearing the weevils in spring 2012 ran into some timing issues. Because these insects require specific plant parts it is critical to have plenty of flowers and fruits available to coincide with egg-laying. However, the Darwin’s barberry plants did not like being grown in pots and failed to produce many reproductive structures. The timing of the shipments also proved to be suboptimal, with too few weevils produced too late in the season for releases to begin. With the benefit of that experience we had another go in spring 2013. “Flowerbud weevils were collected earlier in the season in Chile to try to synchronise better with the early flowerbuds on potted plants at Lincoln,” explained Hernan. However, despite successful egg-laying no new adults emerged from the much damaged flower buds.
A further shipment of weevils (of both species) was hand- delivered by Hernan in October 2013. Although the weevils appeared healthy, routine testing indicated that both weevil species contained microsporidia (internal fungal parasites) and were therefore unusable. Line-rearing to try and remove the microsporidian was not feasible because of the difficulties in producing a steady out-of-season supply of flowers and fruits (which need to remain attached to whole plants to develop) that individual weevils could be caged on, and to ensure adequate hygiene – much more difficult than line rearing the three tradescantia beetles, which we were able to do with sprigs of vegetation in Petri dishes but which nearly did not succeed. Since clean weevils had been collected previously, the next step was to try and identify the best sites to attempt to collect them from next spring.
Fortunately a few weeks after we discovered the imported weevils were diseased, Chantal Probst was due to travel to Chile for phase two of the barberry project to look for plant diseases that could complement the weevils. This meant that Chantal was able to include weevil collections in her November survey. Assisted by Hernan, Chantal was able to bring back 8 populations of the flower bud weevil and 14 populations of the seed feeder. The weevils are currently being checked for disease. “We are hoping to identify at least one site where the weevils appear to be free from infection,” said Lindsay Smith.
Meanwhile, the main reason for Chantal’s survey was successful. She found many signs of disease, including a rust that had previously been identified as worthy of further study when funds permitted. Plant tissues that either had leaf spots or showed dieback were able to be brought back into the new Tamaki plant pathogen containment facility for further study. “I have isolated different fungi from those tissues and they are currently growing on agar plates. The next job is to gene- sequence the different cultures to identify them,” explained Chantal. An application will be submitted to the EPA soon requesting permission to import in containment the kinds of fungi, like rusts, that our current permits don’t allow. Once we have that permission the rust will be imported for further study. In the meantime Hernan has ready some infected plants in safe-keeping.
This project is funded by the National Biocontrol Collective. Dr Hernán Norambuena has been able to travel to New Zealand twice thanks to a fellowship provided by the Agricultural and Marketing Research and Development Trust (AGMARDT).