Sexual communication can contribute to population divergence and speciation because of its effect on assortative mating. We examined the role of communication in assortative mating in the Enchenopa binotata species complex of treehoppers. These plant-feeding insects are a well studied case of sympatric speciation resulting from shifts to novel host-plant species. Shifting to hosts with different phenologies causes changes in life-history timing. In concert with high host fidelity, these changes reduce gene flow between populations on ancestral and novel hosts and facilitate a rapid response to divergent natural selection. However, some interbreeding can still occur because of partial overlap of mating periods. Additional behavioral mechanisms resulting in reproductive isolation may thus be important for divergence. In E. binotata, mating pairs form after an exchange of plant-borne vibrational signals. We used playback experiments to examine the relevance of inter- and intraspecific variation in male advertisement signals for female mate choice in a member of the E. binotata species complex. Female signals given in response to male signals provided a simple and reliable assay. Male species and male individual identity were important determinants of female responses. Females failed to respond to the signals of the two most closely related species in the complex, but they responded strongly to the signals of conspecific males, as well as to those of the most basal species in the complex. Communication systems in the E. binotata species complex can therefore play a role in reproductive isolation. Female responses were influenced by among-individual variation in male signals and females, suggesting the involvement of sexual selection in the evolution of these communication systems.