Midgut infection barriers (MIB) and midgut escape barriers (MEB) that condition dengue type 2 virus (DEN-2) susceptibility in Aedes aegypti (Diptera: Culicidae)

Vector competence of Aedes aegypti for DEN-2 is a quantitative trait conditioned by several loci throughout the genome, and as such can be highly variable. The objectives of this study were to: (1) detect variation in midgut infection (MIB) and midgut escape barriers (MEB) in natural populations of Ae. aegypti, (2) to use marker assisted selection (MAS) to create lines of Ae. aegypti with specific DEN-2 infection phenotypes and test these for susceptibility to other DEN serotypes and genotypes and (3) to use quantitative trait locus (QTL) mapping to identify areas of the genome associated with MEB.; Aedes aegypti collections from Mexico and the USA show extreme variation in MIB, MEB and vector competence (VC) for DEN-2. VC ranges from 24–83%, MIB rates range from 14–59% and MEB rates range from 4–43%. A loose correlation between MIB and MEB suggests the possibility of common genetic factors conditioning these phenotypes.; Ae. aegypti lines with 2 distinct DEN-2 infection phenotypes were created. The D2S3 line is highly susceptible to DEN-2 while the D2MEB line exhibits a large MEB for DEN-2 infection. MAS was not used for selection of these lines. These lines have maintained a high level of fitness over several generations. The susceptibility phenotypes for the D2S3 and D2MEB lines were selected using DEN-2, and are not consistent for other DEN serotypes. This suggests that different genetic factors may quantitatively determine susceptibility to DEN infection for the different serotypes.; QTL mapping was performed using F₁ intercrosses and reciprocal crosses of the D2S3 and D2MEB lines. Two families were used for mapping. In one, the sample size was increased by creating a recombinant inbred line, and the F₅ generation was used for QTL mapping. The increased sample size gave substantially more statistical power in detecting QTL. This crossing design was able to identify 3 QTL for MIB and 8 QTL for MEB.