LANDSCAPE ECOLOGY OF ARBOVIRUSES IN SOUTHERN CALIFORNIA - PATTERNS INTHE EPIZOOTIC DISSEMINATION OF WESTERN EQUINE ENCEPHALOMYELITIS AND ST-LOUIS ENCEPHALITIS VIRUSES IN COACHELLA VALLEY, 1991-1992

Temporal and spatial patterns in the initiation and dissemination of w estern equine encephalomyelitis and St. Louis encephalitis virus activ ity in Coachella Valley during 1991 and 1992 were detected by testing pools of host-seeking Culex tarsalis Coquillett for virus infection an d sentinel chickens for seroconversions. Both viruses repeatedly were detected first at a salt marsh adjacent to the Salton Sea in the south eastern corner df the study area and then disseminated to the northwes t to freshwater marsh, agricultural, and residential habitats. Virus d issemination was relatively slow (<1 km/d) and may have been accomplis hed by dispersive host-seeking mosquitoes. Repeated early-season recov ery of virus activity indicated that both viruses may persist intersea sonally in salt marsh habitat.