Becoming a male Mediterranean fruit fly relies on the newly identified Y-chromosome linked gene - Maleness-on-the-Y (MoY) - which encodes the small protein required to signal male sex determination during development, a new study shows. According to the report, the Y-linked master gene is conserved in several other major fruit fly pests, such as the olive fruit fly and the invasive oriental fruit fly, suggesting it could serve as an important genetic target in efforts to develop more effective gene drive-based pest controls. The globally distributed Mediterranean fruit fly (Ceratitis capitate, or medfly) is widely considered to be one of the most destructive agricultural pests worldwide. While genetic control strategies are useful in suppressing wild medfly populations, a lack of understanding concerning sex determination of the species at the genetic level has limited the effectiveness of similar control strategies in other important Tephritidae pests. Angela Meccariello and colleagues report the discovery of the Y-linked M factor, responsible for activating male sex determination in the medfly. Meccariello et al. show that silencing or disrupting the MoY function in male XY embryos led to the development of fertile females, whilst overexpression of the gene produced fertile males from female XX embryos. What's more, crosses of transformed XY females and transformed XX males yielded offspring, and of both sexes. This indicates that a masculinizing Y chromosome can be transmitted through female meiosis to produce fertile progeny. According to the results, the MoY gene is functionally conserved in other Tephritidae species, which demonstrate similar sex-transformations upon genetic manipulation of the M factor. The discovery of MoY is an important step towards developing strategies to control the destructive members of this particular fly family.