LANDSCAPE ECOLOGY OF ARBOVIRUSES IN SOUTHERN CALIFORNIA - TEMPORAL AND SPATIAL PATTERNS OF VECTOR AND VIRUS ACTIVITY IN COACHELLA VALLEY, 1990-1992

Consistent temporal and spatial patterns in the activity of Culex tars alis Coquillett and western equine encephalomyelitis (WEE) and St. Lou is encephalitis (SLE) viruses were delineated that were useful in deve loping a stratified surveillance program. Vernal increases in Crc. tar salis abundance typically were associated with flooding of saline mars hes along the north shore of the Salton Sea and were followed 6-8 wk l ater by the onset of WEE and SLE virus activity. Viruses then spread t o managed marsh (duck club) and agricultural habitats in the Whitewate r Channel flood plain and, depending upon the intensity of amplificati on, to agricultural and residential areas in the more elevated northwe stern portion of the valley. Mean annual Cx. tarsalis abundance was co rrelated inversely with elevation and distance from the Salton Sea. Ab undance was greatest at managed marsh habitats. Although spatially cor related with vector abundance among sites, virus transmission rates to sentinel chickens were asynchronous temporally with vector abundance. Seroconversion rates were related to flock location but not flock siz e (10 versus 20 chickens). Human cases were not detected during the st udy period, despite elevated transmission rates of both WEE and SLE vi ruses to sentinel chickens positioned in peridomestic habitats.