Mediterranean fruit fly (Ceratitis capitata Weidemann, ‘Medfly’) is currently distributed only in Western Australia. Although occasional detections occur in South Australia and the Northern Territory, they invoke a comprehensive and rapid response to prevent establishment. Medfly previously occurred on the eastern coast of mainland Australia. However, it is believed to have been displaced by Queensland fruit fly (Bactrocera tryoni Froggatt, ‘Qfly’), with the last recorded finding of Medfly in 1941 for New South Wales and 1953 in Victoria. Tasmania has not documented any incursions of Medfly since 1920 and the Northern Territory eradicated the last incursion in 1994. In contrast, Qfly is regularly found in parts of Queensland, New South Wales, Victoria, and the Northern Territory. A species closely related to Qfly, B. aquilonis (May), is established in the Northern Territory and northern Western Australia. Occasional detections of Qfly in South Australia and southern Western Australia result in immediate regulatory actions and eradication activities to ensure that it does not become established. South Australia, Tasmania and the Fruit Fly Exclusion Zone are free from fruit flies of economic concern. Any detections of pest fruit fly species in these areas are immediately quarantined and eradicated. The distribution of Qfly has remained largely unchanged for the last half-century, with established populations along the eastern States and the Northern Territory. The Medfly distribution has also remained unchanged for the last half-century. Qfly and Medfly do not currently co-exist in Australia. This is likely because of the differences in egg-laying habits, competition by larvae in fruit and differences in host range. A similar displacement of Ceratitis by Bactrocera has occurred in other parts of the world.