Abstract: The dominancy of introduced Bactrocera species (Diptera: Tephritidae) over the native fruit fly species was assessed based on data collected from a trapping and sampling program in Morogoro, Tanzania, from 2004 to 2006. Two invasions by Bactrocera species namely the invasive fruit fly Bactrocera invadens Drew, Tsuruta and White and the Solanum fruit fly Bactrocera latifrons (Hendel) have been recorded in 2003 and 2006, respectively. These add to an earlier introduced melon fly Bactrocera cucurbitae (Coquillett). Points and exact times of entry of these species are still unknown. Dominance of Bactrocera species over the native Ceratitis species has been speculated from other parts of the world. Results of this study also suggest the dominancy of Bactrocera species over native Ceratitis species in Tanzania. B. cucurbitae seems to dominate the other cucurbit infesters in terms of abundance and infestation rate. Similarly, B. invadens seems to dominate the native Ceratitis species in orchard fruits in terms of abundance, host range and infestation rate. B. latifrons, whose distribution in the country is still unclear, seems to be the dominant species in its main hosts from family Solananaceae. The outcome of the competition resulting from these introductions is speculated upon. Presence of these pests calls for strong surveillance systems and quarantine regulations to protect the infant fruit industry of Tanzania.