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Herbivorous insects are abundant and diverse and insect–host plant associations tend to be specialized and evolutionarily con-served. Some authors suggested that generalist insect lineages tend to become specialists, with host specialization leading to an evolu-tionary dead-end for the parasite species. In this paper, we have examined this tendency using a phylogenetic tree of Tomoplagia (Diptera: Tephritidae), a parasite of asteracean plants. We have tested the trend towards specialization in diVerent hierarchical degrees of host specialization. The topology of the tree, the inference of ancestral hosts, and the lack of directional evolution indi-cated that specialization does not correspond to a phylogenetic dead-end. Although most Tomoplagia species are restricted to a sin-gle host genus, specialization does not seem to limit further host range evolution. This work emphasizes the advantages of the use of diVerent levels of specialization and the inclusion of occasional hosts to establish a more detailed scenario for the evolution of this kind of ecological association