Queensland fruit fly (Bactrocera tryoni) is a major orchard pest in Australia. Adult flies lay their eggs into ripe fruit, resulting in larval infestation and the spread of bacterial and fungal rots. The role of these microbes in fruit fly ecology is only now being elucidated, with much of the emphasis to date focusing on bacterial communities. In our study, we explored the diversity of yeast species associated with B. tryoni adults and larvae. We found larvae were highly associated with budding yeasts of the genera Hanseniaspora and Pichia across several fruit species. In feeding trials using two yeast species, one species was highly beneficial to larval development and survival whilst the other provided no nutritional benefit. Moreover, adult flies were deterred by the odours produced by the beneficial yeast. Although these findings appear counter-intuitive we discuss how they fit with our understanding of the ecology of this insect, and how this new knowledge could lead to improved monitoring and control of fruit flies in Australia.