Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) is Australia’s most destructive horticultural pest. Suppression methods, including the release of irradiated, sterile individuals (Sterile Insect Technique, SIT) or individuals infected by a common insect symbiont, Wolbachia (α-Proteobacteria) (Incompatible Insect Technique, IIT), are pest management strategies that will become increasingly useful with the introduction of a male-only strain.

To develop a male-only strain of B. tryoni, an understanding of the genes involved in the sex determination pathway, and when they are activated, is necessary. The pathway has been well studied in Drosophila melanogaster (Meigen) (Diptera: Drosophilidae), and this has provided a starting point for characterising genes involved in sex determination in other Diptera. However, the initial signal in male Bactrocera is communicated by the Y-located dominant male determiner, M, which is absent in Drosophila species. The mode of action of M, and its direct targets have yet to be characterised in fruit flies or in any other Y-determined insect.

We utilised a Y-located molecular marker in a related species, Bactrocera jarvisi, to separate male and female embryos at early stages of development. Quantitative PCR pinpointed the timing of important changes in transcript abundance of some sex determination genes, including transformer, transformer-2 and doublesex. Sex-specific poly(A)⁺ transcriptome sequencing, targeting two stages of development, was undertaken and the transcriptomes assembled de novo. Fifteen sex-determination gene homologues and two cellularisation gene homologues of Drosophila melanogaster (Diptera: Drosophilidae) were newly identified in B. jarvisi: extra-macrochaetae (emc) displayed a zygotic transcription profile contrary to the maternal expression in D. melanogaster; sisterless A (sisA) expression occurred very early; slow as molasses (slam) and nullo transcripts increased 80- and 17-fold respectively over time. These data contribute fundamental information to sex-determination research, and provide candidates for the sourcing of gene promoters for transgenic pest-management strategies.