A mark-recapture flight study was conducted in June 2007 with the Mediterranean pine engraver, Orthotomicus erosus, a recently introduced bark beetle in the Central Valley of California. The goal of this study was to estimate dispersal distance to better predict the ultimate impact of the species in North America. These data are essential in preparing a risk assessment for O. erosus. Infested pine logs were collected and placed into rearing cages; emerged beetles were sexed and marked with pink or green fluorescent powder. Fifty-six pairs of Lindgren funnel traps were placed at an open agricultural property (Tulare Co., CA) along five concentric circles with radii of 50, 100, 250, 500 and 1000 m, respectively. Traps in each pair were baited with a newly optimized pheromone or a commercial bait. Three releases of over 6, 000 beetles each were made from the center of the circles. The recaptured beetles were collected once a day until marked beetles were no longer found in the traps. The relative efficacy of the two semiochemical baits will be evaluated. The optimized pheromone performed much better in the recapture of marked beetles, and the beetles dispersed over 1, 000 m within several hours of the release. The temporal and spatial effects of climate conditions (e.g., temperature, humidity and wind direction) on the dispersal behavior of O. erosus will be discussed.