Irradiation is used to disinfest the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) and other pests on mango fruits before export from Thailand to foreign markets. Modified atmosphere packaging (MAP) used during export of mangoes creates a low-oxygen environment that may reduce the efficacy of quarantine irradiation treatment against B. dorsalis. 'Nam Dok Mai' mangoes infested with third-instar larvae of B. dorsalis, wrapped with three different kinds of MAP bags (CF1, FF5, and H34M) or no MAP, were treated with gamma radiation at 0 (control), 30, 60, 90, 120, and 150 Gy. The average O2 and CO2 concentrations in MAP bags with mangos were 7.2 and 8.7% in the H34M bag, 8.6 and 21.2% in the CF1 bag, and 9.6 and 26.7% in the FF5 bag, respectively. The use of MAP on infested mangoes significantly increased mortality of B. dorsalis under irradiation treatment. The estimated lethal doses to cause 99% mortality (LD99) for no MAP and MAP (CF1, FF5, and H34M bags) treatments were 58.1, 41.6, 43.8, and 47.4 Gy, respectively. Therefore, MAP acted as an additional stressor rather than providing radioprotection in irradiated B. dorsalis. Large-scale confirmatory testing of 35,000 B. dorsalis larvae treated at a radiation dose of 150 Gy in mangoes with H34M MAP bags produced no survivors to the adult stage. Commercial use of MAP producing the O2 levels that we observed for mangos in this study will not reduce the efficacy of the approved 150 Gy quarantine irradiation treatment for B. dorsalis.