Population Ecology and Dispersal of Culex Tarsalis (Diptera: Culicidae) in the Coachella Valley of California

During 5 bimonthly experiments in 1993, 55,548 host-seeking and 22,563 newly emerged Culex tarsalis Coquillett females were marked with fluorescent dust and released at a marsh along the Salton Sea. Overall, 3,758 (6.7%) host-seeking and 37 (0.2%) newly emerged females were recaptured in dry ice-baited traps and walk-in red boxes operated for 7-12 consecutive days after release. The recapture of newly emerged females was unexpectedly low and insufficient for further analysis. The recapture rates and dispersiveness of females collected host-seeking within the study area were not different from females collected host-seeking at a site 16 km SE of the release site, indicating that Cx. tarsalis may not rely on memorized flight paths. Loss rates of host-seeking females were high, because many females readily dispersed from the marsh study area during host-seeking flights. Estimates of population size ranged from 914,000 in February to 4,000 in July and were well correlated with catch size in CO2 traps. The wing length and fructose positivity rate of released females did not vary as a function of age or dispersal distance at recapture. Parity of released females increased over time, but nullipars were collected during all recapture periods, perhaps indicating difficulty in blood meal acquisition. Cohort dispersal progressed at the rate of about 0.2 km/d and was sufficient to disseminate arboviruses in the southern Coachella Valley.