A lucky break in Uruguay
Moth plant beetle.
In February, Hugh Gourlay and Hamish Hodgson (Waikato Regional Council) travelled to Uruguay to search for biocontrol agents for moth plant (Araujia hortorum) and woolly nightshade (Solanum mauritianum). Unsure of what they would find there, this excursion into the unknown has provided some muchneeded breakthroughs.
Moth plant and woolly nightshade are mostly problematic in the North Island of New Zealand. Moth plant is an invasive vine, considered one of the worst weeds in Auckland and Northland. Not only is it a threat to native vegetation, but it’s also a nuisance in urban areas, where it invades gardens and parks. The latex sap of moth plant is poisonous and can cause skin irritation. Woolly nightshade is a small, invasive tree, which is also poisonous.
A lace bug (Gargaphia decoris) introduced to attack woolly nightshade in 2010 is showing great potential. Large populations of the lace bug have already built up at some sites, leading to substantial defoliation and even the death of woolly nightshade plants, especially at shaded sites. However, there has always been a question about whether additional agents might be needed to adequately supress this plant in all situations where it is problematic, and some work has been undertaken to explore potential options just in case they are needed.
No agents have been released against moth plant yet. The prospects of successful biocontrol look good, but challenges have arisen with gaining permission to export potential biocontrol agents from South America, causing frustrating delays. A beetle whose taxonomy is currently being clarified (likely Freudeita cupripennis) was approved for release in New Zealand back in 2011. The adults feed on the foliage, but it is the larval stage that is most damaging, feeding on the roots. Efforts to get a shipment of the beetle from Argentina or Brazil, to allow mass-rearing and field releases to get underway, have not been successful. Similarly, efforts to get a shipment of a promising fly (Toxotrypana australis) for further study have been unsuccessful. The larvae of this fly feed inside the pods, destroying the seeds and, if suitable for release here, could potentially reduce the billions of wind-borne seeds that lead to new plants and infestations each year. A rust fungus (Puccinia araujiae), approved for release in New Zealand in 2015, also remains on hold while export permitting issues are resolved.
However, recently an opportunity to try to source the moth plant insects arose in Uruguay, a country in which we have never worked previously. “Thanks to the help of Beatriz Scatoni (Universidad de la República de Uruguay) and Maria Duter (Uruguayan consular representative in New Zealand), we were successful in obtaining a collecting and export permit,” explained Hugh. Although a permit was secured, Hamish and Hugh did not know if they would actually be able to find what they were looking for there. A tephritid fly expert in Uruguay, Soledad Delgado-Jorge, who works with Dr Scatoni, agreed to help with the surveys, as did Soledad Vilamill (Universidad Nacional de Sur), who has been assisting with moth plant insect work in Argentina.
“Our first week in the country was unbearably hot, with high daytime temperatures and no breeze, but fortunately the heat didn’t last and we were able to cover more ground once it was cooler,” said Hugh. While searching around the outskirts of towns and villages in rural Uruguay, Hugh and Hamish were taken to some unpromising sites, such as drainage ditches full of rubbish and debris. However, this is where they struck gold, finding 50 beetles within 5 minutes, and they even found some fly maggots in the moth plant seed pods.
At another site they were accosted by some knife-wielding locals who were enthusiastically pruning grape vines, but despite their offers of help no beetles were collected there. “We weren’t so keen to visit vineyards or orchards, because quite often insecticides are used on these properties, which knock back all the insect life in the area, so roadside ditches and reserves are usually better places to look,” said Hugh. At another site, after battling with thorny acacia bushes, they were rewarded with another 150 beetles. “We were wary of collecting too many early on since we would have to keep them alive for another 10 days until our departure. We had lots of beetles in plastic boxes sitting in the bedroom of my apartment, and were unsure whether they preferred new or old foliage and how long they would live,” Hugh said. Also, the export permit issued by the Ministry of Agriculture in Uruguay only covered insects and not plant material, so Hugh had to be sure the beetles were well fed and would last the journey back to New Zealand without food. As it turned out, 250 beetles made the journey back, with some even producing eggs in transit. The beetles have continued to pump out eggs ever since, allowing various techniques for rearing the beetles to be explored and for their host range to be checked, in case of regional variation.
The flies proved harder to find. “Despite opening over 100 moth plant pods on one day we found no fly larvae,” said Hamish. “Ironically, there was a moth plant growing over the road from our accommodation, which turned out to have some infested pods, but we were only able to bring home a total of 35 pupae,” said Hugh.
The plan is to rear the pupae through to adulthood and get a colony of the fly going in containment to learn more about their biology. There is very little known about the fly, making it a steep learning curve when it comes to keeping them alive or breeding them in captivity. “We will be drawing on all of our collective experience within the biocontrol group,” said Hugh. The team did not encounter the moth plant rust fungus of interest to New Zealand in their travels. Surveys undertaken previously in Argentina have found that the rust is quite rare in the field because of its requirement for fairly wet weather and discovery that it is commonly attacked by a hyperparasitic fungus. Collaborator Freda Anderson (Centro de Recursos Naturales Renovables de la Zona Semiárida, CCT-CONICET Bahía Blanca) has developed a culture of the rust that is free of the hyperparasite, and is keeping it safe for us until an export permit can be issued to allow her to send it to New Zealand.
Once satisfied with their efforts on the moth plant agents, Hamish and Hugh turned their attention to woolly nightshade. They were hoping to find a stem-boring weevil (Conotrachelus squalidus) and a flowerbud-feeding weevil (Anthonomus morticinus), but were also on the lookout for other potential agents of interest. Colleagues in South Africa who had previously looked for biocontrol agents for woolly nightshade in the region were able to offer lots of useful tips. “We were advised by them and others that woolly nightshade mostly grew in the northern and east coast regions, so we headed up there for a few days,” said Hamish.
“The plants we saw were quite heavily damaged, with large branches dead on them, suggesting there were larvae burrowing inside the stems,” Hamish said. “We collected some larvae from these but also noticed a large number of galls on the plants,” explained Hamish. “What was really interesting to me was seeing woolly nightshade growing in its native range, where it isn’t an invasive weed,” said Hamish. “The plants were smaller, with far fewer seeds and much smaller leaves.” A number of insects were collected from woolly nightshade and have been sent away to taxonomists for identification. This will help to determine whether species of interest to the project can be collected from Uruguay in the future.
“I found the trip extremely valuable from a number of points of view,” said Hamish. “It gave me a much better insight into the ups and downs and processes involved with sourcing insects from other countries, and boosted my confidence that biocontrol offers a great opportunity to control invasive weeds like woolly nightshade.” Hamish also had the responsibility of bringing the insects back home. “All our hard work was in my hands and it was a relief when all my bags turned up safely in Auckland,” he said. Another of the trip highlights for Hamish was managing to order a takeaway coffee without sugar in Spanish!
Since returning to the Waikato he has been thinking about good potential release sites for the moth plant beetles. The approval to release the moth plant beetle in New Zealand has lapsed, so a new application will be prepared soon, and the first field releases might be able to get underway as soon as spring 2019.
The moth plant and woolly nightshade projects are funded by the National Biocontrol Collective.
CONTACT
Hugh Gourlay – gourlayh@landcareresearch.co.nz