The high-temperature treatment of eggs of mass-reared tsl genetic sexing strains in Mediterranean fruit fly, Ceratitis capitata (Wiedemann), during late embryogenesis (the low-high protocol) conserves more male flies than treatment during early embryogenesis. A tsl strain, AUSTRIA 6–97, was constructed to follow the fate of aneuploid individuals during male-only production. Aneuploid individuals are produced following segregation in the translocation heterozygous males, and they can survive to the pupal stage where they compromise quality because they do not eclose as adults. Hatching, emergence, and male fly production were quantified and the heat-treatment protocol was characterized. The low-high egg treatment conserves the number of euploid-balanced males, and there is a very low survival of aneuploid males. After heat treatment of eggs, at least 95% of the male pupae were euploid compared with only 71% from untreated eggs. The quality of euploid male pupae was diminished with successive daily collections, an effect previously attributed to aneuploid survivors. Reduced yield of euploid males from early heat treatments was the result of an emergence effect, in addition to a maternal effect. A third detrimental effect of heat was found, occurring after hatching and before pupation, that reduces the survivorship of euploid males. The low-high treatment protocol yielded more males, with a higher accuracy than other heat treatments. However, although it avoids both the maternal and emergence effects, the production of euploid males was 30% less than the potential production, implying that the low-high heat protocol for killing female embryos in tsl genetic sexing strains can be fine-tuned.