There was much excitement for Samoa’s newly launched Natural Enemies – Natural Solutions (NENS) project, with the discovery last week of a new natural enemy (biological control agent) already within Samoa’s borders. The Koster’s curse thrips (Liothrips urichi), is an insect that is known to be an effective natural enemy for controlling the invasive Koster’s curse weed (Miconia crenata previously known as Clidemia hirta) in the Pacific region. It was first used in Fiji in 1930, and 92 years later it has been found in Samoa. This means one less invasive weed to worry about, because the thrips is already effectively controlling the invasive Koster’s curse throughout much of Samoa. The thrips attack the growing shoot tips resulting in smaller, weaker plants and much less seed production. Infestations of the weed now only occur in habitats, like forests, which the thrips are less suited to.
Following the NENS national workshop that focused on prioritizing invasive weed targets for Samoa, the Ministry of Natural Resources and Environment (MNRE), through its Division of Environment Conservation (DEC), and acting on its role as the coordinating agency, joined a team of New Zealand experts from Manaaki Whenua – Landcare Research (MWLR) for surveys and sample collection around Upolu and Savaii. The exercise focused on collecting target invasive weed species samples to be sent to New Zealand for DNA analysis, as well as searching for natural enemies already present in Samoa. During this 3 day activity, the thrips was found feeding on a Koster’s curse plant which sparked much excitement within the team.
Koster’s curse can be an aggressive weed that causes significant damage to agriculture, the environment and to biodiversity. It grows rapidly and can outcompete native plants for both nutrients and space in undisturbed forests and can even halt the growth of native trees. It has been a serious enough pest for many countries around the region that following on from Fiji, Hawai’i, Palau and American Samoa have also taken the step of introducing a biological control agent against the plant.
“We expect that the Koster’s curse thrips has self-introduced from American Samoa, where it was released back in 1974. As is the way with natural enemies like this, the thrips has quietly gone about its job of reducing Koster’s curse infestations un-noticed while not harming any other plants,” said MWLR NENS programme lead, Lynley Hayes.
“It was important to know that the thrips is already in Samoa, so other weeds can be prioritized for attention instead. The thrips now joins the list of other natural enemies in Samoa which have safely and successfully controlled weeds, including giant sensitive plant (Mimosa diplotricha) and lantana (Lantana camara).”
For context, NENS is the practice of introducing safe natural enemies into a country to manage invasive weeds when eradication is deemed non-feasible and the impacts of the weeds are serious enough to require intervention. Before any natural enemy is released, extensive research is done and the natural enemies are selected against a strict criteria to determine safety and to ensure there is no possibility of them causing problems to non-target plants. In many situations, NENS is the least damaging, and most cost-effective, and sustainable method for controlling weeds when compared to other control methods such as the use of chemical control (herbicides) – it is also more realistic when compared to manual control methods.
MNRE would like to thank the experts from MWLR – Dr. Quentin Paynter, Lynley Hayes and Temo Talie – for your interest in working with Samoa to get our NENS programme up and running and for providing an opportunity for our local staff to build their capacity and knowledge on the use of natural enemies for invasive weed control and its processes.
The NENS is a regional Programme of the Pacific Regional Invasive Species Management Support Service (PRISMSS) based at the Secretariat of the Pacific Regional Environment Programme (SPREP) office. The Samoa NENS component is funded by the New Zealand Ministry of Foreign Affairs and Trade’s (MFAT) “Managing Invasive Species for Climate Change Adaptation in the Pacific” (MISCCAP) project and is under the coordination of MNRE.
MNRE DEC and Forestry reps collecting invasive weed samples in Savaii