The vector competence of Culiseta incidens (Thomson) and Culex thriambus Dyar for West Nile virus (WNV) were compared to Cx. quinquefasciatus Say or Cx. tarsalis Coquillett and Cx. stigmatasoma Dyar collected concurrently in California. Culiseta incidens were less susceptible to oral infection than Cx. quinquefasciatus, but transmitted virus at a significantly higher rate, thereby yielding comparable population transmission rates. Culex thriambus was equally susceptible to oral infection and transmitted virus at rates comparable to Cx. tarsalis or Cx. stigmatosoma. A mammalian host selection pattern most likely precluded detection of natural infection in Cs. incidens, a fairly abundant peridomestic species. In contrast, an avian host selection pattern and efficient vector competence resulted in repeated detection of WNV in Cx. thriambus; however, limited abundance and restrictive riparian larval habitat requirements would seem to limit the involvement of Cx. thriambus in WNV epidemiology.