Within the past 10 years, the yellows disease ‘bois noir’ (BN) has become one of the commercially most important diseases of grapevine [Vitis vinifera L. (Vitaceae)] in Europe. Infection pressure is caused by phytoplasmas of the stolbur 16SrXII-A group that are transmitted by a planthopper vector, Hyalesthes obsoletus Signoret (Homoptera: Auchenorrhyncha). Infestation happens as an accidental side-effect of the feeding behaviour of the vector, as vector and pathogen proliferation is dependent on other plants. In Germany, the increase of BN is correlated with the use of a new host plant by the vector, increase in abundance of the vector on the new host plant, and dissemination of host plant-specific pathogen strains. In this article, we investigate geographic and host-associated range expansion of the vector. We test whether host-plant utilization in Germany, hence the increase in BN, is related to genetic host races of the vector and, if so, whether these have evolved locally or have immigrated from southern populations that traditionally use the new host plant. The genetic population analysis demonstrates a recent expansion and circum-alpine invasion of H. obsoletus into German and northern French wine-growing regions, which coincides with the emergence of BN. No H. obsoletus mitochondrial DNA haplotype host-plant affiliation was found, implying that the ability to use alternative host plants is genetically intrinsic to H. obsoletus. However, subtle yet significant random amplified polymorphic DNA (RAPD) genetic differentiation was found among host plant populations. When combined, these results suggest that a geographic range expansion of H. obsoletus only partly explains the increase of BN, and that interactions with host plants also occur. Further possible beneficial factors to H. obsoletus, such as temperature increase and phytoplasma interactions, are discussed.