1. Population connectivity and movement are key ecological parameters influencing the impact of pests, and are important considerations in control strategies. For many insects, these parameters are difficult to assess directly, although they may be assessed indirectly using population genetic data. 2. We used microsatellite markers to examine population genetic structure of the western cherry fruit fly, the main pest of cherry crops in western North America, in British Columbia, Canada, and make inferences about connectivity and potential for movement among populations. 3. Comparing populations from four geographical regions (separated by up to approximately 400 km), we found significant genetic differentiation both among and within regions. Using populations as the units of analysis, we observed significant isolation by distance (IBD) at larger spatial scales but not below approximately 20 km. By contrast, using individual flies as the units of analysis, we found significant IBD at scales as small as < 100 m. We saw no evidence of genetic differentiation among populations sampled from different species/varieties of plants. 4. Our results suggest that the movement of individual flies is limited, although high levels of gene flow are maintained at scales of up to 20 km, possibly through combined effects of stepping-stone gene flow and large population sizes.