1. The document examines genetic variation in the montane willow leaf beetle (Chrysomela aeneicollis) and growth patterns of its host plant (Salix orestera) in the Eastern Sierra Nevada Mountains. 2. In 2011, an early freeze provided an opportunity to study how genetic differences at loci PGI and COII relate to beetle survival and development. Beetles with genotype PGI 1-1 had lower survival rates than those with PGI 4-4. Those with haplotype h3 were more likely to reach adulthood before the freeze than those with h1. 3. Growth of S. orestera varied among sites and elevations. Higher