Annual emergence patterns of Culex nigripalpus females before, during and after a widespread St. Louis encephalitis epidemic in south Florida.

Resting Culex nigripalpus females were collected from the same site at least 3 times a week from January 1986 through December 1991. Newly emerged mosquitoes were used to monitor annual emergence patterns that were rainfall driven. Four of the years, 1986-89, preceded the 1990 St. Louis encephalitis (SLE) epidemic in south Florida. The pre-epidemic period averaged 4 emergences per year, with most occurring during July and August. The emergence patterns observed during the epidemic year were unusual in their early start in May and June and in the total number (11) observed. Adult mosquito emergences in 1991 were similar to those in 1990, with an early start and a total of 14 observed, yet no SLE transmission was recorded in Indian River County during 1991. A time series analysis of the 6-year data set showed a significant cross-correlation between the emergence of Cx. nigripalpus females and heavy (> 50 mm) rains. A significant adult emergence occurred 5-8 days and 12-15 days following a heavy rainfall event.