06/22/2026
Chrysolina! Cry-so-line-uh! Chrysolina! We can’t stop saying it!!
Did you know that even medicinal plants can become noxious w**ds outside of their native habitat? That’s right, St. Johnswort (Hypericum perforatum), a plant popularly known for its medicinal uses, is a noxious w**d in parts of North America. It is a perennial that grows 1 to 3 feet tall. It has bright yellow star-shaped flowers and leaves that look “pin-pricked” when held up to the light. Luckily for us, we have a biocontrol agent for it as well! The Klamath Beetles (Chrysolina hyperici and C. quadrigemina), which we at MTBCP like to simply call Chrysolina, are a moderately effective biocontrol for the w**d.
The larvae feed at nighttime on young foliage in the early spring as the plant begins to bolt. Once they have pupated into adults in the early summer, they feed on the foliage of flowering plants. Once they finish feeding, the adults rest in the soil until fall rain stimulates them to lay eggs on any remaining plant foliage. The eggs then overwinter and hatch in the spring. However, if there is not enough rain to stimulate egg production, the adults will overwinter and lay eggs the following spring. The feeding done by the larvae can decimate populations of St. Johnswort, and the defoliation caused by adults inhibits the plant’s ability to photosynthesize.
Fun fact, the plant foliage makes the larvae of these beetles photosensitive, meaning they don’t want to be in the sun. As a result, the larvae primarily feed before sunrise. The adults can be seen out feeding during the heat of late spring and early summer.
**dManagement **ds
