Expression patterns of sex‐determination genes in single male and female embryos of two B actrocera fruit fly species during early development

In tephritids, the sex‐determination pathway follows the sex‐specific splicing of transformer ( tra ) mRNA , and the cooperation of tra and transformer‐2 ( tra‐2 ) to effect the sex‐specific splicing of doublesex ( dsx ), the genetic double‐switch responsible for male or female somatic development. The D ominant Male D eterminer ( M ) is the primary signal that controls this pathway. M , as yet uncharacterized, is Y ‐chromosome linked, expressed in the zygote and directly or indirectly diminishes active TRA protein in male embryos. Here we first demonstrated the high conservation of tra , tra‐2 and dsx in two A ustralian tephritids, B actrocera tryoni and B actrocera jarvisi . We then used quantitative reverse transcription PCR on single, sexed embryos to examine expression of the key sex‐determination genes during early embryogenesis. Individual embryos were sexed using molecular markers located on the B . jarvisi   Y ‐chromosome that was also introgressed into a B . tryoni line. In B . jarvisi , sex‐specific expression of tra transcripts occurred between 3 to 6 h after egg laying, and the dsx isoform was established by 7 h. These milestones were delayed in B . tryoni lines. The results provide a time frame for transcriptomic analyses to identify M and its direct targets, plus information on genes that may be targeted for the development of male‐only lines for pest management.