The dispersal ability of Trichogramma ostriniae Pang and Chen, a biological control agent of Ostrinia nubilalis Hübner, was studied in commercial potato fields on the Eastern Shore of Virginia. The purpose was to quantify dispersal of T. ostriniae after an inundative release to aid in determining the number of release points needed per unit area for effective biological control of O. nubilalis in solanaceous crops. A single release of approximately 0.5 million wasps was made in two spatially separate potato fields in summer 2005 and 2006. Each release area contained 25 monitoring points at distances from 5 to 45 m from the release point bearing a yellow sticky card and O. nubilalis egg sentinels to observe for adult parasitoids and parasitism, respectively. Results showed that movement of T. ostriniae adults from the release point was rapid with individuals captured at 45 m within 1 d of emergence. High rates of parasitization (20-50%) also were observed at this distance, but the levels decreased with increasing distance from the release point. The distances that encompassed 98% recaptured T. ostriniae adults (x(98)) were 27.5 and 12.9 m from the release point in 2005 and 2006, respectively. The (x(98)) distances for parasitization of O. nubilalis were 21-26 m in 2005 and 8-10 m in 2006. However, the highest levels of parasitization in both years occurred nearest the release point. T. ostriniae showed uniform dispersal within an area of approximately 0.1 ha, indicating that multiple release points should be used for effective dispersal of T. ostriniae and control of O. nubilalis in solanaceous crops. Based on the assumption that a distance of 16 m represents the radius around a release point in which T. ostriniae activity was at its maximum, we estimate that approximately 12 release points/ha would be required in potato fields.