Does variation in Culex (Diptera: Culicidae) vector competence enable outbreaks of West Nile virus in California?

William Reisen, Chris Barker, Ying Fang, Vincent M. Martinez

Research output: Contribution to journalArticlepeer-review

53 Scopus citations


Since the invasion of California by West Nile virus (family Flaviviridae, genus Flavivirus, WNV) in 2003, we have annually monitored vector competence for the NY99 strain in Culex tarsalis Coquillett, Culex pipiens quinquefasciatus Say, Culex p. pipiens L., and Culex stigmatosoma Dyar populations from four areas: deserts of Coachella Valley, densely urbanized maritime Los Angeles, southern San Joaquin Valley in Kern County, and southern Sacramento Valley near Davis in Sacramento County. Overall, Cx. stigmatosoma was the most competent vector species, followed by Cx. tarsalis and the Cx. pipiens complex. The median infectious dose (ID 50) of WNV required to infect 50% of the F1 female progeny reared from wild-caught females, a measure of mesenteronal susceptibility, ranged between 5 and 8 log 10 plaque forming units/ml and was not correlated with annual human case incidence or summer maximum likelihood mosquito infection estimates. Odds ratios comparing nonoutbreak years with referent outbreak years were variable and failed to show a distinct pattern for Cx. tarsalis or Cx. pipiens complex females. Apparently factors other than midgut susceptibility within the ranges we measured enabled WNV outbreaks in California. Culex populations remained competent for St. Louis encephalitis virus, indicating that the disappearance of this virus was not related to a loss of vector competence.

Original languageEnglish (US)
Pages (from-to)1126-1138
Number of pages13
JournalJournal of Medical Entomology
Issue number6
StatePublished - Nov 1 2008
Externally publishedYes


  • Culex pipiens complex
  • Culex tarsalis
  • St. Louis encephalitis virus
  • Vector competence
  • West Nile virus

ASJC Scopus subject areas

  • Insect Science
  • veterinary(all)
  • Infectious Diseases
  • Parasitology


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