The program will focus on two partially overlapping themes in the hope of contributing to the eventual control of arthropod-borne viral infections. The themes will be, 1) dengue viruses; their epidemiology, their interaction with mosquitoes, and the diagnosis, pathogenesis, and prevention of disease they produce, and 2) the interaction between mosquito-borne viruses in general and all stages of the life cycle of their vectors, with emphasis on aedine species. Five scientific projects are proposd. The first is a study of the genetics of the competence of Aedes aegypti as a vector for the dengue viruses, with the long-range objective of developing virus-resistant strains of Ae. aegypti for liberation in the field. A second is a study of the factors which affect the transovarial transmission of dengue viruses by mosquitoes, with the objective of obtaining information which can be utilized to evaluate the importance of such transmission for survival of dengue viruses in nature under adverse environmental conditions. The third is a study of the suitability of various species of Toxorhynchites mosquitoes as hosts for the isolation and propagation of arboviruses, with the objective of developing one or more species as useful laboratory animals. The fourth has as its principal objective the search for field evidence of transovarial transmission of Japanese encephalitis virus in Asia. The fifth is a study of the relationship between factors which affect hatching of aedine mosquito eggs and the survival and replication of transovarially transmitted arboviruses.