Biology and Impacts of Pacific Islands Invasive Species. 13. Mikania micrantha Kunth (Asteraceae)

Abstract: Mikania micrantha Kunth, commonly known as bitter vine, American rope, or mile-a-minute, is a rapidly growing vine, native to tropical America. Mikania micrantha is present in 20 Pacific island countries and territories, including Australia, the Cook Islands, Fiji, French Polynesia, Micronesia, Papua New Guinea, Samoa, Solomon Islands, and Vanuatu. A CLIMEX model based on native distribution of M. micrantha suggests that most of the islands in the Pacific, southern Asia, and parts of southern and central Africa are climatically suitable for M. micrantha, leaving these areas vulnerable to new or further incursions. Its rapid spread is a threat to both natural and agricultural environments, where it kills or reduces growth of preferred species, severely impacting on biodiversity and production. Large numbers of wind-dispersed seeds and ability to propagate vegetatively from stem fragments facilitate rapid invasion. Management of M. micrantha is difficult. Several postemergence herbicides exhibit some efficacy, but manual control via hand pulling and slashing is more commonly practiced. However, slashing may result in increased growth from fragments, and plants may regenerate from roots after herbicide application. Cultural techniques such as fallowing or burning may also help limit spread. Competitors that produce ample vegetation such as sweet potato (Ipomoea batatas [L.] Lam.) may be effective for suppression in some situations. Various studies have shown that Mikania micrantha exhibits some genetic diversity across biotypes encountered in southern Asia. Although little is currently known about its population genetics across the South Pacific, more information will undoubtedly facilitate potential for future biological control. A rust pathogen, Puccinia spegazzinii, introduced from South America was established in Taiwan in 2008, in Papua New Guinea and Fiji in 2009, and in Vanuatu in 2012 for biological control. The dodder Cuscuta campestris Yuncker has also shown some efficacy against M. micrantha, but its status as a known pest limits its use as a biological control agent. Recent research into the mikania wilt virus as a biocontrol agent is in its infancy, and it is too early to recommend it to assist with the management of M. micrantha. Given the difficulty of controlling M. micrantha once established and the early stages of research into biological control, high priority must be given to preventing colonization of Pacific islands where M. micrantha is not yet present, through early detection and rapid response to new incursions.