31 October 2024, Alofi Niue - Niue will be welcoming a leaf-feeding beetle that researchers hope will turn the tide against the invasive weed known as air potato, or locally as hoi.
As the technical lead for the Pacific Regional Invasive Species Management Support Service (PRISMSS) Natural Enemies – Natural Solutions (NENS) Programme researchers from Manaaki Whenua – Landcare Research (MWLR) will make the first delivery in the Pacific of the air potato leaf beetle (Lilioceris cheni), a natural enemy of the air potato (Dioscoria bulbifera), in early November.
The PRISMSS NENS programme aims to lower the impact of widespread invasive plants. Led by MWLR, NENS reduces the vigour of widespread weeds through reuniting them with safe natural enemies from their original homeland. The NENS programme initiatives empowers Pacific communities by improving the health and well-being of all living things and ecosystems.
The beetles have been raised in Manaaki Whenua’s Invertebrate Containment facility in Lincoln, near Christchurch, New Zealand, and will be released in Niue in collaboration with the Environment Department, with the help of National Invasive Species Co-ordinator Mr Huggard Tongatule.
“Using natural enemies against invasive weeds in Niue can provide long-term cost-effective and natural control that is so desperately needed here,” says Mr Tongatule.
“Hoi is widespread here and has proven to be a very costly and labour-intensive weed to remove, especially for farmers with crop plantations.”
Mr Tongatule says a workshop in early 2020 ranked hoi as a top priority action against weeds in Niue.
Air potato, a fast-growing vine with heart-shaped leaves and potato-like bulbils, is native to Asia and possibly tropical America. It has become invasive in several Pacific Islands, including Fiji, French Polynesia, Niue, Palau, Tonga, and Wallis and Futuna. Air potato is now widely naturalised in tropical and subtropical regions around the world.
While the air potato leaf beetle is a new natural enemy for the Pacific, the beetle has been extensively studied by researchers in the United States and was first released in Florida and other southern states in 2012. Adult beetles chew lots of round holes in the leaves, and larvae eat the leaf tissue, leaving just the skeletonised veins of the leaf. Collectively they provide an effective and low-cost way of controlling air potato.
Manaaki Whenua Senior Researcher and lead of the NENS Programme, Ms Lynley Hayes says while the beetles are a first for Niue, beneficial organisms have been used before on the island to manage invasive weeds.
“It has been 20 years since four natural enemies were released in Niue to control two weeds: giant sensitive plant (Mimosa diplotricha) and lantana (Lantana camara),” Ms Hayes says.
“The release of the air potato beetles marks a restart in the use of this important technique for managing key invasive weeds in Niue.”
Thick mats of air potato can quickly smother native vegetation, causing native plant communities and other biodiversity to decline, which in turn affects ecosystem functioning. Air potato also infests agricultural land, reducing crop yields. Evidence suggests that vines benefit from increasing carbon dioxide in the atmosphere and will become even more invasive and harmful in the future.
Since air potato grows on and becomes entangled with other plants, including native and beneficial plants, it is difficult to apply herbicide without also killing these. Manual removal is very time-consuming. The plant can quickly resprout from its network of underground tubers and will also grow from cut vines and bulbils, which can survive for a long time even if they are buried under soil.
There are several varieties of air potato in Niue. The beetles will attack all forms of air potato, but no other plants are at risk, including closely related important cultivated yams such as Dioscorea alata (ufi), D. esculenta (ufilei) and D. pentaphylla (pilita).
Mr David Moverley, The Secretariat of the Pacific Regional Environment Programme’s (SPREP) Invasive Species Adviser, commented that “plants with tubers, bulbs, rhizomes or other types of storage mechanisms can be problematic to control without the use of specific herbicides, because of their ability to regenerate.”
“It is great to see some relief in sight for the people of Niue from the air potato. The use of natural enemies will hopefully reduce the work required to constantly mange this plant across the landscape, allowing time and effort to be spent on more rewarding activities in daily life and reduce the impact this plant is having on natural ecosystems in Niue.”
Better management of the invasive form of air potato is clearly needed to improve food security and reduce environmental harm, but this requires a slight trade-off in that the edible forms of air potato will need to be protected from the beetles. However, the beetles won’t ever eradicate any variety of air potato, just reduce their abundance.
The beetles will be directly released in the field where they will gradually build up in numbers, dispersing to all air potato infestations on the island over time. This process can be accelerated by collecting up and moving beetles around if necessary.
The research work on air potato is a part of the PRISMSS Restoring Island Resilience programme, which is funded by New Zealand’s Ministry of Foreign Affairs and Trade and administered by SPREP. The introduction of the air potato to Niue is also supported by the Global Environment Facility’s Regional Invasives Project (GEF-6).
While the beetles are expected to play a useful role in the management of a key invasive species in Niue, this project paves the way for similar projects in other Pacific islands also affected by this weed, and for projects against other serious weeds such as taro vine (Epipremnum pinnatum cv aureum), for which natural enemies are currently being sought.
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About PRISMSS: The Pacific Regional Invasive Species Management Support Service (PRISMSS) is a coordinating mechanism designed to facilitate the scaling up of operational management of invasive species in the Pacific. PRISMSS brings together experts to provide support within the Pacific region with a focus on protection of indigenous biodiversity and ecosystem function. As a service provider, PRISMSS provides a comprehensive suite of support services in a cohesive, effective, efficient, and accessible manner to Pacific Island countries and territories.
Restoring Island Resilience (RIR): The PRISMSS - Restoring Island Resilience (RIR) is a New Zealand-PRISMSS collaboration project that aims to improve Pacific Island Countries and territories livelihoods and resilience to climate change by reducing the impact of invasive species on natural and agricultural ecosystems through the five PRISMSS programmes.
The GEF 6 Regional Invasives Project (RIP) is funded by the Global Environment Facility, implemented by the United Nations Environment Programme, and executed by the Secretariat of the Pacific Regional Environment Programme. The Project works primarily in the Marshall Islands, Niue, Tonga, and Tuvalu and has a regional component. Implementation of the GEF 6 RIP is supported by the Pacific Regional Invasive Species Management Support Services (PRISMSS).