4 March 2025, Vava’u, Tonga: African tulip tree (Spathodea campanulata), originally from tropical Africa, is a destructive alien weed in the Pacific region that invades indigenous forests and arable land causing a reduction in natural biodiversity and agricultural productivity.
As part of efforts to battle this invasive weed, a recent monitoring survey of a natural enemy of African tulip tree on Vava'u has been conducted, delivered promising results and marking a significant step forward in safe, long-term, sustainable weed control in Tonga.
The survey was conducted by experts from the Tonga Ministry of Meteorology, Energy, Information, Disaster Management, Environment, Climate Change & Communications (MEIDECC), Ministry of Agriculture, Food and Forests (MAFF) and New Zealand’s Manaaki Whenua - Landcare Research (MWLR), as part of the Natural Enemies - Natural Solutions (NENS) programme.
NENS is a programme of the Pacific Regional Invasive Species Management Support Service (PRISMSS), led by the Secretariat of the Pacific Regional Environment Programme (SPREP), which supports Pacific Island Countries and Territories in restoring ecological balance using natural enemies from the weeds' native range. MWLR is the technical lead for the NENS programme.
Traditional control methods, such as manual removal and herbicide application, have proven too costly and labour-intensive. The NENS programme offers a safe, self-sustaining solution by introducing highly specific natural enemies from the weed’s native range to curb its growth.
A gall-forming mite (Colomerus spathodeae) and a leaf-mining flea-beetle (Paradibolia coerulea) are being deployed in the Pacific to help manage the weed. Both are African tulip tree specialists and will not attack any other plants. Historically, successful control using NENS is often positively correlated with the number of natural enemy species released and it is expected that the combined impact of both natural enemies will be needed to reduce the invasiveness of African tulip tree.
Moreover, work on developing a third natural enemy, a pod and stem borer (Sinomphisa junctilinealis), is underway, which could also potentially be deployed in the future, if required, to further suppress African tulip tree.
A survey of African tulip trees performed by MAFF and MEIDECC between 2022-2023 across the islands of Tonga confirmed that invasion by African tulip tree is set to become a significant issue for Tonga, with invasion most advanced in Vava’u.
The survey revealed that the tree is now too widespread on Vava’u and Tongatapu for management through conventional control to be a cost-effective or a feasible solution, so the African tulip mite was released on Vava’u in December 2023.
A year later, teams from MAFF, MEIDECC and MWLR have returned to Vava’u to determine the success of the release.
NENS Programme Coordinator, Ms Indigo Michael, based at MWLR shared, “monitoring surveys are part of every Natural Enemies - Natural Solutions project and are performed by technical experts to determine whether establishment at release sites had occurred, whether the agent has spread, and to confirm no non-target attack has occurred.”
“Follow up surveys are also performed to record any early impacts on weed populations following the release of natural enemies. Establishment of the mite was confirmed at all sites where it was released and it was found on African tulip trees at least 4km from any release site, indicating that the mite is now widespread on the island. Due to its small size, the mite disperses readily in the wind, travelling from tree to tree easily.”
While the mite is too small to be seen with the naked eye, obvious symptoms of its impacts can be seen on African tulip trees across the island - conspicuous galls (technically erinea) on the leaves and leaf petioles. These telltale signs can be used to confirm whether a tree has been colonised by the mite.
"This is exactly what we hoped to see at this stage," said Dr. Quentin Paynter, a natural enemies’ expert from MWLR. "The gall mite is settling in well, and some African tulip tree seedlings are already looking quite stunted.”
“It’s a good start although I suspect that additional natural enemies may be required to cause a significant reduction in the vigour and dominance of mature African tulip trees, allowing native species to reclaim lost ground.”
The use of natural enemies is a rigorously tested approach that prioritises safety and effectiveness. Before any natural enemy is released, it undergoes years of research to ensure it targets only the problem species without harming beneficial plants or other biodiversity.
SPREP Invasive Species Adviser, Mr David Moverley, commented, “African tulip is a major problem in much of the region. Melanesia, Micronesia and Polynesia are all being impacted by this plant, some have been trying to manage it for a long time.”
“We are hoping that the use of these natural enemies can benefit other countries and territories in the region to lower the spread and impact of African tulip. Members who are interested in this approach should contact PRISMSS here at SPREP.”
The African tulip tree natural enemies have passed extensive tests, demonstrating its host-specificity and long-term viability as a control tool. No evidence of non-target attack was found, as expected, confirming that the mite attacks only the targeted weed, African tulip tree.
The results from this survey indicate a hopeful future for managing African tulip tree in Tonga. As monitoring continues, researchers will track the biocontrol agent’s progress and refine strategies for its long-term success.
With continued support, natural enemies could play a vital role in managing not only African tulip trees but also other invasive species threatening the region’s unique biodiversity.
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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).
For more information:
Mr Viliami Hakaumotu
National Invasives Species Coordinator - Tonga
viliamihakau@gmail.com
Ms. Indigo Michael
NENS Programme Coordinator – Manaaki Whenua Landcare Research
michaeli@landcareresearch.co.nz
For additional information please contact Mr Domnic Sadler, PRISMSS Manager on dominics@sprep.org or Mr Nitish Narayan, PRISMSS Communications & Liaison Officer on nitishn@sprep.org