The New World screwworm (NWS), Cochliomyia hominivorax (Coquerel) (Diptera: Calliphoridae), is a parasitic insect pest of primary importance in Neotropical regions. Because of the economic losses caused by this pest to livestock rearing, an international effort has been involved in a program to control the NWS from endemic areas of Central and South America and to prevent invasions into screwworm-free areas. In order to maximize the effectiveness of area-wide control approaches, it is essential to characterize the genetic variability of target populations. Therefore, sixteen microsatellite loci are currently being used to investigate the genetic variability and population structure across NWS current geographic distribution. Preliminary results obtained from Uruguayan populations indicated a high genetic variability. Although previous mtDNA data indicated that this species form a single panmitic population in Uruguay, results from microsatellite analysis yielded low, but significant, levels of subdivision between populations. These results can be explained by the differences in the modes of inheritance of these two markers or by a female-biased gene flow among these populations. However, the sex-biased dispersal should be further investigated, since these populations did not show evidence of isolation by distance. Therefore, the observed differences between local populations are probably a result of a shared history (recent colonization). Patterns of genetic variation, structure and gene flow are important information required prior to an investment on large-scale efforts aiming at control of insect pests. Such information should provide support for decision makers in the planning and implementation of new area-wide control programmes. Support: FAPESP, IAEA.