In Colombia, malaria is one of the most important health problems. The regions most affected are the "Uraba, Bajo Cauca and Alto Sinu" and the Pacific Coast and we propose to focus our studies in these two northwestern areas. Some localities in these two regions have experienced significant changes in human migration and land use. Our studies will test the hypothesis that regional changes may have altered mosquito species composition, which has subsequently resulted in the increased parasite transmission observed in this region. Our preliminary studies in northwestern Colombia have confirmed the presence of several Anopheles species, some in the Nyssorhynchus subgenus. Members of this subgenus have been recognized as primary vectors or vectors of regional importance in other Latin American countries and have the potential to be secondary or regionally important vectors in Colombia. Accurate identification of some Nyssorhynchus species using morphological keys is very difficult due to cryptic morphology and intraspecies variation, limiting confirmation of species and preventing incrimination of vector species at the local level. Our goal is to provide updated entomological information in two areas of Colombia most critically affected by re-emerging malaria by addressing the following Specific Aims. In Aim 1, we will accurately inventory Anopheles species in localities from these two areas using morphological characters and molecular assays. In Aim 2, we will assess the epidemiological importance of these species using Plasmodium-specific PCR-ELISA of definitively identified mosquitoes. We hypothesize that primary vectors incriminated in other regions may have become established and now predominate in these regions. Similarly, species that co-occur with suspected vectors may in fact be more important in transmission based on patterns of abundance and parasite infection prevalence. Data from the pilot studies proposed herein will establish a current inventory of Anopheles species and malaria parasite infection prevalences in localities in Uraba-Bajo Cauca-Alto Sinu and the Pacific Coast, regions that are most affected by re-emerging malaria in Colombia. In future studies, we will focus on the population genetics of the identified primary vector species for the establishment and maintenance of successful targeted control programs. Specifically, studies of population genetics of primary vector species can be used to develop predictive models of malaria transmission, to predict and assess the success of control measures, and to predict and monitor the spread of insecticide resistance genes.