Depending on spring conditions, adult beetles emerge from hibernation about mid-May in Illinois and begin feeding. Oviposition begins soon, with eggs and beetle larvae seen in June. After eggs hatch, young larvae feed on and damage the growing tip, preventing growth, flowering and, therefore, seed production. Older larvae feed on and skeletonize the leaves. Full-grown larvae then move down the stems to pupate below the plant.
New adults emerge in late summer, feed, and prepare for overwintering.
Usually only one generation per year is seen. Biological Control of Purple Loosestrife in Illinois Biological control of purple loosestrife is being implemented in many states, but the project in Illinois is one of the strongest.