The beetles are a natural enemy being used for the first time in the Pacific islands to try to reduce the spread and density of the invasive African tulip tree. After a year-long search to find a safe way to transport them from their quarantine in South Africa, the beetles arrived in New Zealand in late February just as Auckland went into a COVID lockdown that halted all flights to our Pacific neighbours. The enforced and extended stay at the Manaaki Whenua - Landcare Research (MWLR) containment facility in Auckland led to the beetles growing too old to be released.
In response to this setback the team got to work rearing a new generation of beetles to be ready for when travel to the Cook Islands was possible.
“We already had African tulip tree (Spathodea campanulata) plants growing in our containment facility, so we were able to keep a culture going,” said MWLR Research Leader Dr Quentin Paynter.
“It has taken some careful rationing of the plants to rear enough beetles for a field release and ensure that they haven’t demolished all our plants. We also need to keep a back-up culture in case the first release fails.”
Dr Paynter and MWLR Weed Biocontrol Technician Stephanie Morton released the beetles in the Cook Islands this past weekend.
“Our colleague at the Cook Islands Ministry of Agriculture, Dr Maja Poeschko, located a suitably isolated release site that is safe from public health staff spraying insecticides for mosquito control to combat dengue fever,” says Dr Paynter.
“We initially released 40 beetles in four nylon rearing sleeves, to keep them contained and ensure beetles didn’t rapidly disperse so their offspring couldn’t find one another. We set 26 free (just in case we hadn’t chosen an ideal release site). When we returned to the site 2 days later we easily found several of the freely released beetles, indicating they did like the release site.”
The African tulip tree is considered one of the 100 worst alien invasive species in the world and one of the top 30 terrestrial invasive plants. MWLR researchers and their collaborators at Rhodes University in South Africa have been seeking specialist natural enemies to reduce the spread and density of the invasive African tulip tree, which is problematic in the Pacific Region for several years.
A gall mite (Colomerus spathodeae) which forms leaf galls that stunt new growth has already been successfully established in Rarotonga. It is expected that the combined impact of both agents will be needed to reduce the invasiveness of African tulip tree. Rigorous testing has confirmed that both the mite and the beetle are African tulip tree specialists that pose no risk to other plant species in the Pacific region.
The African tulip tree project is an example of one of the many projects in the Pacific region working to enable the Pacific Island countries and territories (PICTs) to take stronger action against invasive species and build resilience to climate change. This collaborative effort is funded by New Zealand’s Ministry of Foreign Affairs (MFAT) and sees MWLR join forces with the Secretariat of the Pacific Regional Environmental Programme (SPREP), and the New Zealand Department of Conservation (DOC).
MWLR’s Science Team Leader Lynley Hayes say the work on stopping invasive weeds is vitally important. “Recent reports suggest children in the Pacific are suffering even more due to poor nutrition under COVID and climate change. Weeds contribute to this problem by making it more difficult to produce food.”