Post-colonization-adaptation
Guides
Chrysolina quadrigemina
greater St. John's wort beetle, St. John's wort beetle
Chrysolina quadrigemina is a leaf beetle introduced to North America as a biological control agent for the invasive weed Hypericum perforatum (St. John's wort). Native to Europe and North Africa, this beetle has established populations across western North America and has been introduced to Australia. Adults and larvae feed exclusively on Hypericum species, with documented spillover onto native congeners such as H. punctatum in the eastern United States. The beetle exhibits a univoltine life cycle with adults active in summer, and shows evidence of post-colonization adaptation to colder climates in northern populations.