How did Chrysolina beetles help control Saint-John’s-wort in the western United States?

In the western United States, Chrysolina beetles were introduced as a form of biological control to manage the invasive Saint-John’s-wort, also known as Klamath weed (Hypericum perforatum).1

Beginning in California in 1945, two species of Chrysolina beetles—along with one species of the genus Agrilus—were released to feed on the weed. These insects were chosen because the plant had been introduced to the region without its natural predators, allowing it to spread unchecked. Following their introduction, the beetles spread rapidly and became established in California, Oregon, Washington, and Idaho by 1950. Through their feeding activity, the insects successfully reclaimed approximately 1 million hectares (2.5 million acres) of rangeland from the invasive plant.1