Decreased plant vigor results from larval feeding. Egg laying commences in early July and continues until mid-September. About 50 eggs per female beetle are laid in leaf axils of diffuse knapweed. Larvae hatch from eggs in about 2 weeks. The first instar feeds in leaf axils.
Second instars penetrate leaf petioles and migrate into the root crown.
Usually only one larva will survive and flourish in the root crown. Larvae overwinter in the root crown and begin feeding again in the spring. Pupation occurs within the root crown during July. Adults emerge in July directly through the root crown and produce only one generation per year. Smaller knapweed plants are stunted or killed by larvae.