Seasonal abundance of Culex nigripalpus Theobald and Culex salinarius Coquillett in north Florida, USA
Zyzak, M.; Loyless, T.; Cope, S.; Wooster, M.; Day, J.F.
Journal of Vector Ecology Journal of the Society for Vector Ecology 27(1): 155-162
2002
ISSN/ISBN: 1081-1710 PMID: 12125867 Document Number: 547558
North Florida is a transition zone between widespread Culex nigripalpus populations to the south and focal Culex salinarius populations to the north. Culex nigripalpus is a vector of St. Louis encephalitis (SLE) and eastern equine encephalitis (EEE) viruses in south Florida, while C. salinarius is a suspected New World vector of West Nile (WN) virus. Abundant vector populations are often a prerequisite for epidemic and epizootic transmission of arboviruses. Extensive SLE transmission has never been reported from north Florida, but sporadic WN transmission was reported there during the summer of 2001. The disparate flavivirus transmission patterns observed in north and south Florida may be due, in part, to the local geographical and seasonal distribution of Culex vectors. Here we report that between May 1991 and April 1994, C. salinarius was most commonly observed during the winter and spring in northeast Florida (Duval County), whereas C. nigripalpus was most abundant during the summer and autumn. An unusually mild spring in 1991 allowed C. nigripalpus to reproduce early in the year, resulting in a summer population that emerged more than 8 weeks earlier than in 1992 and 1993. The 1991 C. nigripalpus population persisted through October, when SLE transmission was detected by sentinel chickens. Transmission of SLE was not detected in Duval County in 1992 or 1993. These data indicate that mild winter and spring conditions in north Florida may favour increased abundance and survival of C. nigripalpus in a region where this species is normally not abundant. A seasonal shift in population structure may increase the transmission risk of arboviruses for which C. nigripalpus is a competent vector, including SLE, WN, and EEE.