Genetic variation for West Nile virus susceptibility in Culex tritaeniorhynchus

Mutant and geographical strains of Culex tritaeniorhynchus were compared for West Nile (WN) virus susceptibility by feeding on a high-titered blood-virus suspension. Eleven strains also were selected from 2-21 generations for an increase and/or a reduction of oral susceptibility using 90% and 10% infective virus doses, respectively. Only one of the 20 strains tested, e ma, was significantly less susceptible than the control strain. In the selection experiments, none of the strains showed a consistent decrease in susceptibility, but the Changa Manga II (CM) strain showed a sustained increase in susceptibility from generations F11-F21 when selection was discontinued. Reciprocal cross-matings and back-crosses were set up between the selected CM strain and two of the morphological mutant strains, e ma and re e ae, carrying homozygous recessive markers. The resulting progeny were tested for susceptibility to WN virus infection and the ability to replicate virus to high-titers after infection. These results suggest that the trait of increased susceptibility is dominant over resistance. The enhanced ability of infected mosquitoes to replicate WN virus showed partial dominance. Both of these traits appear to be polyfactorial, and are apparently associated with more than one chromosome in Cx. tritaeniorhynchus.