According to the biological species concept, species are defined as reproductively isolated entities that are separated from one another by barriers to gene flow. An increasing body of research demonstrates that many such barriers, e.g. differential host choice, are ecological in nature. Ecological isolating barriers can, however, be modified by environmental disturbance. If non-ecological barriers, e.g. hybrid sterility, are incomplete an environmental disturbance will result in the breakdown of reproductive isolation between two species. Here we show that two Rhagoletis (Diptera: Tephritidae) sibling species are perfectly isolated via differential host choice, but incompletely isolated via host-independent mate choice. The introduction of non-native honeysuckle did provide, however, a third host that is accepted by both taxa. As mating in Rhagoletis occurs exclusively on the host, exotic honeysuckle served as a rendez-vous point for both species that led to the local breakdown of reproductive isolation. Our results suggests that in species that are primarily isolated via ecological factors species status is dependent on environmental variables that can change in space and time.