Overwintering larvae emerge in early spring and feed on common St. Johnswort foliage (typically at night) when the plant is bolting. They develop through five instars. Pupation occurs in the soil. Adults emerge in late spring and early summer and lay eggs on St. Johnswort foliage. Larvae of the first new generation emerge in midsummer as common St. Johnswort flowers, repeating the life cycle. Second generation larvae hatch in late summer, coinciding with the late flowering stage of common St. Johnswort, and feed on foliage and flowers. This generation overwinters in the larval stage within the soil. There are up to two generations per year, depending on winter temperatures. Warm, dry, and long summers are needed to complete both generations. When cold temperatures arrive too soon, second generation larvae do not survive winter. Adults are usually fewer in number in the first generation compared to the second generation.