Photo: Pasifika delegates take part in the “Natural Enemies, Natural Solutions” breakout session at the International Symposium on Biological Control of Weeds.

Have you ever wondered how invasive species make their way into a country? In the past, most arrived by ship, often accidentally. Today, they can also enter by plane. Some species are introduced deliberately, such as for ornamental use, while others slip in unnoticed.

In the Cook Islands, several well-known invasive species arrived through these pathways. The ship rat came ashore unintentionally on early vessels. Common myna birds were introduced to help control pests, and the African tulip tree was brought in as an ornamental plant. Over time, all three spread rapidly, placing increasing pressure on native ecosystems. To manage their populations, a range of control methods are used, including physical removal, chemical treatments, and biological control.

Biological control, or “biocontrol,” involves using living organisms, such as insects, fungi, or diseases, to suppress invasive species. One example in the Cook Islands is the introduction of the Red postman butterfly to combat the invasive Red passion vine. The vine had been spreading aggressively and smothering native vegetation.

Before the butterfly was released in 2016, it underwent extensive testing to ensure it would only target the red passion vine. Researchers observed its feeding and breeding behaviour in controlled environments with a variety of plant species. These trials confirmed that the butterfly laid its eggs exclusively on the target vine, indicating minimal risk to other plants. Such testing can take months or even years, and even after release, the species continues to be closely monitored by organisations like Manaaki Whenua – Landcare Research.

More recently, Manaaki Whenua – Landcare Research hosted the International Symposium on Biological Control of Weeds in Rotorua. The event brought together experts, governments, and organisations, including Te Ipukarea Society and the National Environment Service, to share global experiences. While many biocontrol efforts have been successful, others have faced challenges, such as agents failing to establish or concerns about potential risks preventing their release.

The symposium also provided an opportunity for Pacific countries to learn from one another. A key focus was the African tulip tree, one of the most widespread invasive species in the region, known for outcompeting native plants. It is ranked among the world’s worst invasive species.

To control its spread in the Cook Islands, the gall-forming mite Colomerus spathodeae was released in 2016 and quickly became widespread, damaging the tree. This was followed by the release of the African tulip beetle in 2021. Monitoring is ongoing, but early observations from Landcare Research indicate the beetle is establishing well and feeding on the tree’s leaves.

Across the Pacific, countries have taken different approaches. Some have released only one biocontrol agent, while others rely more heavily on mechanical removal or chemical treatments, particularly where infestations are less severe. Sharing these experiences helps strengthen regional strategies and improve future outcomes.

Managing invasive species is a shared responsibility. It requires coordinated efforts from governments, NGOs, and international partners. However, prevention remains the most effective tool. Customs and biosecurity systems form the first line of defence in keeping harmful species out.

While these systems continue to improve, the public also plays a vital role. By following biosecurity regulations and being mindful of what we bring into the country, we can all help protect our environment.

Protecting our islands starts at the border, but it continues with every one of us.