Technical Abstract: Pseudacteon curvatus Borgmeier is one of three species of phorid fly parasitoids currently approved for release in the U.S. as self sustaining biological control agents for suppression of the red, black and hybrid imported fire ants. Previous studies showed that in the spring of 2002 a biotype of P. curvatus from Las Flores, Argentina, that prefers black and hybrid imported fire ants, was released in a 3.25 ha grazed pasture (Knox site) in Clay Co., MS. By September 2002, flies had established and were reported to have spread up to 600 m from the original release site. Additional releases during the springs of 2002 and 2003 were made in a grazed pasture (Prima site) located 8.8 km SE of the Knox site. Fly presence was confirmed at both sites during 2003. From May to September of 2004, observations outside the release sites showed that the flies had multiplied and dispersed to occupy an ellipsoidal area that encompassed more than 2249 km2 or over 224,914 ha. Flies were found over 44 km in a bearing 356o NW, 37 km in a bearing 162o SE, 24 km in a bearing 70o NE and 11 km in a bearing 291o NW of the Knox site. Average dispersal was 14.5 km/year with a range of 5.5-22 km/year. The successful establishment of phorid flies will hopefully reduce the competitive advantage of imported fire ants thus allowing the native ant species to more effectively compete for natural resources.