Genetic analysis of transosvarial transmission of La Crosse virus in the eastern treehole mosquito, Aedes triseriatus

Abstract

The genetic basis of transovarial transmission (TOT) of La Crosse virus in Aedes triseriatus was investigated through selection experiments on two mosquito strains. The Holmen strain was subject to selection for TOT refractoriness, the AIDL strain for permissiveness to TOT. Response to selection for a low filial infection (FI) rate was rapid, decreasing from 18% to 3% in three generations. However, no response to selection for permissiveness was observed in the AIDL strain: the average FI rates through four generations fluctuated between 25% and 40%. By contrast, TOT rate in both strains showed a consistent response to selection in both directions. These patterns were consistent with a model in which TOT is controlled by a single genetic locus and permissiveness is conditioned by dominant alleles; while FI rate is not under genetic control, being influenced by environmental factors associated with the mosquito and virus. Additionally, a RAPD-SSCP linkage map consisting of 72 polymorphic markers was constructed for Ae. triseriatus. The estimated size of individual chromosomes was 93 cM for chromosome I, 63 cM for chromosome II, and 37 cM for chromosome III. The estimated length of the entire linkage map was 193 cM, with an overall resolution of one marker every 2.7 cM. This map was used to explore the genetic basis of TOT and female-biased sex ratios consistently observed in our Ae. triseriatus strains. In quantitative trait locus (QTL) mapping experiments carried out on separate families, TOT and sex were scored as binary quantitative characters. Two QTLs affecting TOT were mapped to chromosome I and four QTLs affecting sex ratio were also located on chromosome I.