The goal of this research is to delineate the evolutionary potential and gene-structure-biological function relationships of bunyaviruses in their arthropod vectors at the organism, organ, and cell level. The molecular events which occur during infection and transmission of California serogroup viruses in their mosquito vectors will be determined. These events will be examined at the level of replication and transcription and translation of viral RNA species. These experiments will entail the production and use of a series of molecular reagents, including gene and strand specific DNA probes and immune reagents specific for structural and nonstructural virus proteins. These reagents will permit us to follow the course of viral RNA and protein synthesis within the vector and will permit identification of aberrant viral RNA species which might arise during the infection of the vector. These aberrant RNA species may be potential genomes of DI particles and may be involved in virus interference and modulation. The molecular basis of bunyavirus development in and transmission by vectors will also be defined using parental and defined-clone RNA segment reassortant viruses. Determination of bunyavirus gene contributions to vector-virus interactions should permit a better understanding of factors operative in the maintenance of arbovirus cycles in nature. The potential for RNA segment reassortment and generation of new reassortant viruses will be determined in dually infected vectors. In addition, the potential for spontaneous bunyavirus mutation in persistently (transovarially) infected vectors will be investigated. Members of the Bunyaviridae are of considerable medical and veterinary importance. Determination of the evolutionary potential of the viruses by RNA segment reassortment and by spontaneous mutation combined with knowledge of the molecular events and genetic determinants of bunyavirus infection and subsequent transmission by vectors might indicate which way the epidemic potential of the viruses would evolve.