Seasonal Genetic Changes of Aedes aegypti (Diptera: Culicidae) Populations in Selected Sites of Cebu City, Philippines.

Aedes aegypti (L.) is the primary vector of dengue virus in the Philippines, where dengue is endemic. We examined the genetic changes of Ae. aegypti collected from three selected sites in Cebu city, Philippines, during the relatively wet (2011-2012) and dry seasons (2012 and 2013). A total of 493 Ae. aegypti adults, reared in the laboratory from field-collected larvae, were analyzed using 11 microsatellite loci. Seasonal variation was observed in allele frequencies and allelic richness. Average genetic differentiation (DEST=0.018; FST=0.029) in both dry seasons was higher, due to reduced Ne, than in the wet season (DEST=0.006; FST=0.009). Thus, average gene flow was higher in the wet season than in the dry seasons. However, the overall FST estimate (0.02) inclusive of the two seasons showed little genetic differentiation as supported by Bayesian clustering analysis. Results suggest that during the dry season the intense selection that causes a dramatic reduction of population size favors heterozygotes, leading to small pockets of mosquitoes (refuges) that exhibit random genetic differentiation. During the wet season, the genetic composition of the population is reconstituted by the expansion of the refuges that survived the preceding dry season. Source reduction of mosquitoes during the nonepidemic dry season is thus recommended to prevent dengue re-emergence in the subsequent wet season.

A set of broadly applicable microsatellite markers for analyzing the structure of Culex pipiens (Diptera: Culicidae) populations.

Microsatellite markers were isolated and developed from Culex pipiens quinquefasciatus Say (Diptera: Culicidae) sampled in Johannesburg, South Africa, to identify those that are broadly useful for analyzing Cx. pipiens complex populations between continents. Suitable loci should be 1) inherited in a codominant Mendelian manner, 2) polymorphic, 3) selectively neutral, 4) randomly associated, 5) without null alleles, and 6) applicable across broad regions and between diverse biotypes. Loci in Cx. p. quinquefasciatus from Johannesburg ranged from two to 17 alleles per locus and expected heterozygosities (H(e)) were 0.02-0.87. Loci in Cx. p. pipiens L. from Johannesburg had five to 19 alleles per locus and H(e) values ranging from 0.57 to 0.93, whereas those from George, South Africa, had five to 17 alleles per locus and H(e) values ranging from 0.54 to 0.88. Loci in North American mosquitoes were more variable. Cx. p. quinquefasciatus from South Carolina had five to 19 alleles per locus and H(e) values ranging from 0.64 to 0.90, whereas Cx. p. pipiens from Massachusetts had six to 28 alleles per locus and with H(e) values ranging from 0.65 to 0.94. All loci were associated randomly. Overall, four of nine of these new loci satisfied all six criteria for broad utility for analyzing the genetic structure of Cx. pipiens populations.

Gene flow among populations of the malaria vector, Anopheles gambiae, in Mali, West Africa.

The population structure of the Anopheles gambiae complex is unusual, with several sibling species often occupying a single area and, in one of these species, An. gambiae sensu stricto, as many as three "chromosomal forms" occurring together. The chromosomal forms are thought to be intermediate between populations and species, distinguishable by patterns of chromosome gene arrangements. The extent of reproductive isolation among these forms has been debated. To better characterize this structure we measured effective population size, N(e), and migration rates, m, or their product by both direct and indirect means. Gene flow among villages within each chromosomal form was found to be large (N(e)m > 40), was intermediate between chromosomal forms (N(e)m approximately 3-30), and was low between species (N(e)m approximately 0.17-1.3). A recently developed means for distinguishing among certain of the forms using PCR indicated rates of gene flow consistent with those observed using the other genetic markers.