Genetic Differentiation Among Populations of Culicoides variipennis (Diptera: Ceratopogonidae), the North American Vector of Bluetongue Virus

Abstract

Genetic relationships among 24 populations of Culicoides variipennis (Coquillett) were examined using isozyme electrophoresis of 21 protein-encoding loci. Estimates of genetic similarity based on gene frequency differences among populations were consistent with the existence of three North American subspecies, C. v. occidentalis Wirth & Jones, C. v. sonorensis Wirth & Jones, and C. v. variipennis. A stepwise discriminant analysis determined several allozymes which, when used in two canonical variables, accounted for 97% of the dispersion between subspecies. The geographic and genetic relationships among the three subspecies provide support for the hypothesis that the subspecies may be different species. The genetic relationships of the three subspecies to C. gigas Root & Hoffman suggest that C. v. occidentalis diverged from a C. variipennis-like ancestor from which C. v. sonorensis and C. v. variipennis later evolved. The implications of the genetic structure of the C. variipennis complex for the epidemiology of bluetongue disease in North America are discussed.