Abstract: A three-year survey was conducted to evaluate population density of Western Black Flea Beetle (WBFB), Phyllotreta pusilla Horn (Coleoptera: Chrysomelidae) and their movement on cultivated crops and non-cultivated habitats throughout the growing season in Colorado (USA). The western black flea beetle was recovered from mid-April to early August during three year sampling periods. Therefore, they have multiple generations in Colorado. The first WBFB populations also appeared winter mustard such as Flixweed, Descurainia spp. and moved to canola from wild mustards to caused significant injury during seeding stages of canola. Knowing the population density of WBFB and their movement outsides of canola crops is important to predict their injury to canola plants and for developing new control strategies.