Abstract Herbivore attack has important consequences on plant performance and on plant community composition, and understanding plant responses to herbivory is important for improving our ability to predict community dynamics and in developing biological control programs. The first objective of our study was to assess the response of purple loosestrife (Lythrum salicaria) to various levels of tissue loss (0, 10, 20, and 60–70%) caused by feeding by a chrysomelid beetle (Galerucella calmariensis) introduced as a biological control agent to North America. Leaf beetle herbivory changed flowering phenology, caused significant reductions in plant growth and inflorescence mass, and increased the branching pattern even in the lowest herbivory treatment. In general, plant performance measures (height, total length of inflorescence) decreased linearly with increasing defoliation level. A second objective was to evaluate whether commonly used artificial herbivory techniques (hole punching and clipping) can reproduc...