Temporal and geographic genetic variation in Culex nigripalpus theobald (Culicidae: Diptera), a vector of St. Louis encephalitis virus, from Florida.

A field population of Culex (Culex) nigripalpus Theobald from Vero Beach, FL sampled monthly over a period of 24 mo, a colony sample and 10 geographic samples were analyzed for genetic variation at 14 enzyme loci using polyacrylamide gel electrophoresis. The Cx. nigripalpus colony sample showed significantly lower genetic variation than the field-collected samples, measured by mean number of alleles per locus (colony 1.4 +/- 0.1 versus field 2.1 +/- 0.22), percentage of polymorphic loci (colony 35.7% versus field 54.8 +/- 7.7%), but mean observed heterozygosity (Ho = colony 0.16 +/- 0.07 versus field 0.17 +/- 0.03) and mean Hardy-Weinberg expected heterozygosity (He = colony 0.14 +/- 0.06 versus field 0.18 +/- 0.02) did not differ significantly. Three of the 14 loci (Aldox, Gpd, and Gpi) from the Vero Beach field samples showed distinct temporal patterns in the frequency of the most common allele. Higher mean observed heterozygosity (Ho) occurred during months following high rainfall in the Vero Beach field samples than during months following low rainfall. The average Nm value of 3.6 indicated high gene flow among the temporally distributed samples of the Vero Beach population. Genetic variability values between geographic samples from Panhandle, FL and south Florida were not significant. Gene flow estimates based on F(ST) = 0.039 provided a Nm of 6.2 indicating high levels of gene flow among the geographic samples of Cx. nigripalpus. The average Nei's and modified Rogers' genetic distances among the 10 populations were 0.009 +/- 0.001 and 0.081 +/- 0.004, respectively. The cluster analysis did not suggest geographic clustering, Because Cx. nigripalpus is the vector of St. Louis encephalitis (SLE) in Florida, temporal and geographic genetic variation in this species is discussed in relation to the seasonal and geographic SLE virus activity in Florida.

Survival of arboviruses in trypanosome-infected triatomines.

The potential of triatomines to maintain arboviruses was demonstrated by the ability of Rhodinius prolixus with experimentally punctured abdomen to harbor Venezuelan equine encephalitis (VEE) virus for at least 4 months and St. Louis encephalitis virus for 1 month. At 30 days after infection VEE virus was found at low titers in Trypanosoma cruzi-infected R. prolixus and at moderate titers in T. rangeli-infected R. neglectus. Transmission of VEE virus by bite of punctured bugs was successful 2 weeks after virus ingestion; attempts at 30 days failed.