In mid-June, two Bioeconomy Science Institute, Manaaki Whenua Group staff, Quentin Paynter and Lynley Hayes, travelled to Rarotonga to monitor the establishment and spread of the African tulip tree beetle (Paradibolia coerulea). In collaboration with the Cook Islands National Environment Service, Ministry of Agriculture and the Te Ipukurea Society, this beetle was introduced there in 2021 to control the African tulip tree (Spathodea campanulata). This invasive tree is considered one of the world’s 100 worst invasive species and is widespread in Rarotonga. Biocontrol of African tulip tree is one of the flagship projects of the Natural Enemies – Natural Solutions (NENS) programme led by MW-BSI, which sits under the Pacific Regional Invasive Species Management Support Service.
Image: African tulip tree flea beetle
After conducting their monitoring checks, Quentin and Lynley were delighted to report that the African tulip tree beetle is exceeding their expectations. Signs of the beetles were found at all five release sites, with significantly more damage than in June 2024 when the release sites were last monitored. Every size of the African tulip tree, from small plants to large trees, in the sun and the shade, are being attacked. Moderate damage was common on all plants inspected up to 500m away from the release point. The beetles are dispersing well as the NENS team found signs of them on most plants checked all around the island, even on isolated plants around Avarua, the capital of the Cook Islands. Given most of the beetle releases were only made in 2022, their performance at this early stage bodes extremely well for successful biocontrol of African tulip tree.
Image: adult beetles feeding in the canopy
Lynley highlighted that “the Cook Islands is leading the way with using natural enemies to control African tulip tree in the Pacific. The release of the African tulip tree beetle in Rarotonga in 2021 was a world first.” The extent of the problem only became apparent in Rarotonga following some remote sensing work done in 2023 which revealed the infestation to be much more extensive than previously thought. “We were shocked to see the extent of African tulip tree spread across the entire island” said Paul Peterson, a Bioeconomy Science Institute, Manaaki Whenua Group senior technician who led the work in Rarotonga. Paul, Andrew McMillan and Ben Jolly (all from the Manaaki Whenua Group) used satellite, aerial and drone imagery to estimate that 1.6% of Rarotonga’s land area was infested with the African tulip tree. This work is discussed in more detail in Issue 106.
Since controlling African tulip tree using herbicides or mechanical means is expensive and labour intensive, biocontrol was sought as a solution. With the help of Rhodes University in South Africa the African tulip tree beetle was introduced to Rarotonga from Ghana. Both the adults and larvae damage the African tulip tree. As adults, this flea beetle feeds on the upper leaf surface of the African tulip trees, removing leaf material of the host plant and leaving feeding holes. When disturbed, the beetles are capable of rapidly jumping, hence the name flea beetle. The adults lay eggs on the leaf surface, and the emerging larvae burrow into the leaf and mine within the leaf structure. They remove large amounts of leaf tissue without breaking the epidermal layers of the leaf.
MW-BSI is working with Fiji, Samoa, Tonga and Vanuatu who all hope to be able to release the beetle before the end of 2025. Tonga is currently rearing the beetles, and Fiji is also preparing to start rearing the beetles once the import permit is approved. In Samoa, importation and rearing will begin once an upgrade to facilities is finished in September.
Along with the African tulip tree beetle, the African tulip mite (Colomerus spathodeae) is another biocontrol agent for the African tulip tree. It was released in 2016 in Rarotonga and has established well in the Cook Islands. This mite forms galls on the new leaves and shoots of the African tulip tree, diverting nutrients that the tree would otherwise use for growth and reproduction. Galling ranges from slight to heavy with some significant damage to growing tips of the African tulip trees observed.
To complement the damage from the African tulip tree beetle and mite, Rhodes University is currently working to explore the suitability of a new pod and shoot-feeding moth found in Cameroon for this invasive tree. All in all, the biocontrol programme for African tulip tree is going very well.
This work was initially supported by the Managing Invasive Species for Climate Change Adaptation in the Pacific project, funded by New Zealand’s Ministry of Foreign Affairs and Trade (NZMFAT). Since July 2024 it has been supported by the Restoring Island Resilience project, also funded by NZMFAT, and administered by the Secretariat of the Pacific Regional Environment Programme as part of the Pacific Regional Invasive Species Management Support Service.
