In November last year Niue welcomed the air potato leaf beetle (Lilioceris cheni), which researchers hope will turn the tide against the invasive weed known as air potato (Dioscoria bulbifera), or locally as hoi. As the technical lead for the Pacific Regional Invasive Species Management Support Service (PRISMSS) Natural Enemies – Natural Solutions (NENS) Programme, MWLR researchers made the first delivery of the leaf-feeding beetle in the Pacific.
Image: air potato leaf beetle – Lilioceris cheni.
The beetles were reared in MWLR’s Invertebrate Containment facility at Lincoln and were released in collaboration with Niue’s Environment Department, with the help of the National Invasive Species Coordinator, 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,” said Huggard. “Hoi is widespread here and has proven to be a very costly and labour-intensive weed to remove, especially for farmers with crop plantations.” Huggard noted that a workshop in early 2020 ranked hoi as a top priority for action against weeds in Niue.
Air potato, a fast-growing vine with heart-shaped leaves and potato-like bulbils, is native to Asia. It has become invasive in several Pacific Islands, including Fiji, French Polynesia, Niue, Palau, Tonga, and Wallis and Futuna. Air potato is also widely naturalised in tropical and subtropical regions around the world.
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 ones, it is difficult to apply herbicide without also harming them. Manual removal is very time-consuming and challenging because the controlled plants can quickly resprout from their network of underground tubers and will also grow from cut vines and bulbils, which can survive for months even if they are buried under soil.
Although 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 many round holes in the leaves and larvae eat the leaf tissue, leaving only the skeletonised veins of the leaf. The beetle provides an effective and low-cost way of controlling air potato.
Lynley Hayes, leader of the NENS Programme, said that while the air potato beetle is 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),” Lynley said. “The release of the air potato beetle marks a restart in the use of this important technique for managing key invasive weeds in Niue.”
No other plants are at risk from the air potato beetle, including closely related cultivated yams such as Dioscorea alata (ufi), D. esculenta (ufilei), and D. pentaphylla (pilita). David Moverley, Invasive Species Advisor of the Secretariat of the Pacific Regional Environment Programme (SPREP), commented that “It is great to see some relief in sight for the people of Niue from air potato. The use of natural enemies will hopefully reduce the work required to constantly manage this plant across the landscape, allowing time and effort to be spent on more rewarding activities in daily life. Its impact on natural ecosystems in Niue should also be reduced.”
The beetles have been 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 and moving beetles around if necessary.
The air potato beetle is expected to play an important 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.
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 the Secretariat of the Pacific Regional Environment Programme (SPREP). The introduction of the air potato to Niue is also supported by the Global Environment Facility’s Regional Invasives Project (GEF-6).
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