Variation in male body size, age, and prior sexual experience may all influence male mating success in tephritid fruit flies. Bactrocera tryoni (Froggatt) is an Australian pest tephritid for which the sterile insect technique (SIT) is being actively pursued, and for which information on what makes males more competitive is urgently needed. Pair-wise competitive mating trials were run using laboratory-reared flies in walk-in field cages, evaluating young, large, and virgin B. tryoni males against old, small, and nonvirgin males, respectively. Analysis of male sexual competitiveness indices revealed that young and large males obtained significantly more copulations compared to old and small males; there was no significant difference between virgin and nonvirgin males in obtaining mates. While SIT programs will always release young males, the results do show that rearing programs which focus on producing larger males, rather than greater numbers of smaller males, will produce more sexually competitive males. After release, virgin SIT males will not be at a competitive disadvantage with sexually experienced males based on prior mating experience.