Although Thrips tabaci is a well-known vector of Tomato spotted wilt virus (TSWV) it does not belong to the spreaders of this dangerous pathogen in North America. The possible explanation of the differences in its vector efficiency in Europe and in North America is rooted in the fact that out of the two subspecies of T. tabaci, i.e. T. tabaci tabaci and T. tabaci communis only the specimens of the latter were introduced from Europe into North America. To support our hypothesis we have used a molecular marker that detects intraspecific ribosomal DNA sequence variations between the two subspecies of T. tabaci.