The Queensland fruit fly, Bactrocera tryoni (Froggatt), is the most significant pest of edible fruit in Australia. For the control of B. tryoni using sterile insect technique (SIT), either pupae or adults may be released. Using pupal release, this study tested the seasonal effect of different pupal loadings on eclosion and the flight of sterile B. tryoni. Pupal eclosion boxes were loaded with either 200, 350, 500, 650 or 800 g of pupae during five periods of the fruit fly season (August, October, December, February and April). Adult flies were allowed to emerge and the remaining pupal debris was sampled to determine the per cent emergence and per cent fliers. The duration of emergence, dye retention on the ptilinum of the flies, and temperature and relative humidity externally and internally of the eclosion boxes were recorded. The percentage of emergence was influenced by both pupal loading and the period of release. Overall, the percentage of emergence was lower for loadings of 200 and 350 g of pupae in August, October and April as compared with the 500 g or higher loadings. This difference was not apparent in December or February. The mean percentage of emergence for each pupal loading in December, February and April was well above 65%, the minimum required emergence parameter for successful sterile B. tryoni release. Across all pupal loadings, the percentage of fliers was greater than 99.3% in December, 87.8% in February and 80.8% in April. A high percentage of fliers (>92.7%) was recorded in October, but the percentage of emergence in August and October was below 65% for all pupal loadings; thus pupal release is a suboptimal SIT method during this period of time. Dye on the ptilinum was detected on every fruit fly sampled across all pupal loadings and release periods. Minimum temperature for optimal pupal emergence should not fall below 10°C, and the maximum should not exceed 35°C. Minimum temperature for successful flight should not fall below approximately 6°C while the maximum temperature should exceed 16°C. The described pupal release system is considered a possible option for use as part of an SIT program against B. tryoni under suitable environmental conditions in Australia.