Pupation occurs in the soil or leaf litter at the base of plants. New generation adults emerge from late June to August. Both species occur throughout the native range of purple loosestrife in Europe and Asia. Both species have been released in over 27 states and 6 Canadian Provinces. G. calmariensis is more common since the species was easier to mass produce than G. pusilla .
Adults are very mobile and possess good host finding abilities.
Peak dispersal of overwintered beetles is during the first few weeks of spring. New generation beetles have dispersal flights shortly after emergence and can locate host patches as far as 1 km away within a few days. Long range dispersal might occur over much larger distances. Less severe attack will result in reduced shoot growth, elimination of seed production, and particularly reduced root growth. Galerucella attack also increases the branching pattern of purple loosestrife.