Koster's Curse: The Invasive Plant Devastating Hawaii

Clidemia hirta, infamously known as Koster's Curse, was first documented on O'ahu in 1941. This aggressive, shade-tolerant shrub, native to Central and South America, rapidly colonized forests, pastures, and cultivated lands across the Hawaiian Islands. Its arrival in the Pacific predates Hawaii, as it became a significant pest in Fiji during the late nineteenth century.

The plant's name and introduction to Fiji are shrouded in mystery, with two primary accounts. One suggests seeds were accidentally mixed with coffee shipments around 1880-1886, leading to its naming after a planter named Koster. Another account, recorded in 1924, attributes its introduction to William Fillingham Parr as an ornamental plant, with the name 'Koster's Curse' arising from a misheard identification.

In Hawaii, Koster's Curse poses a severe threat to native ecosystems. It thrives in forest understories and gaps, with its dense growth preventing regeneration of other plants. Birds disperse its seeds, with each fruit containing around 500 seeds, facilitating rapid spread. Invasive pigs also contribute to its dissemination by carrying seeds on their hooves.

To combat this invasive species, biological control agents are being employed. Liothrips urichi, a thrips previously used in Fiji, has been introduced to Hawaii. Additionally, the clidemia gall wasp, Allorhogas clidemiae, is being considered, with its larvae altering fruit formation to prevent seed viability. Host-specificity trials are crucial before any potential release.