RESUMEN
We tested for host-associated genetic differentiation in 22 populations of Thrips tabaci collected from tobacco and leek, respectively. Clustering analyses and haplotype networks based on sequence variation at a fragment of the mitochondrial cytochrome oxidase I gene yielded three major evolutionary lineages; two were clearly associated with leek and the third with tobacco. These genetic findings corroborated recent experimental observations on the heterogeneity of T. tabaci populations with regard to host-plant preference and their capacity to be vectors for tomato spotted wilt virus. Estimated divergence times suggested an ancient divergence of these lineages dating back to the Miocene 28-21 million years ago. F(ST) values between these lineages ranged between 0.824 and 0.954 (P<0.001 for all comparisons), and sequence divergences ranged between 4 and 11%. Given these findings and by the standards of genetic and ecological differentiation in other published species groups, T. tabaci must be considered a complex of cryptic (sub)species.