A recent publication in Insect Science by researchers from Justus Liebig University Giessen presents the development and functional validation of a minimal, intronless version of the white pupae (wp) gene in Ceratitis capitata, commonly known as the Mediterranean fruit fly.

The wp phenotype—characterized by white-colored pupae—has long been used as a selectable marker in Genetic Sexing Strains (GSS), which are essential for large-scale, male-only releases in Sterile Insect Technique (SIT) programs. Traditional GSS rely on chromosomal translocations that link selectable markers to the Y chromosome. While effective, such methods can reduce fertility and introduce genetic instability.

The study introduces a compact version of the wp gene—termed mini-wp—measuring just 4.7 kb compared to the full wild-type allele of 20 kb. This construct was shown to fully restore the wild-type brown pupal phenotype in wp-mutant strains, even when integrated at different genomic locations, including the X chromosome. Importantly, the rescue was functional both in homozygous and heterozygous states.

These findings represent an important step toward the “neo-classical” GSS approach, which seeks to use genome editing to precisely insert selectable markers, such as mini-wp, into the Y chromosome. Smaller genetic constructs like mini-wp are more amenable to such targeted insertion techniques, potentially improving the efficiency, stability, and scalability of GSS for SIT applications.

Beyond Ceratis capitata, the methodology developed in this study may be adapted to other Tephritid species where the wp gene has been identified, supporting broader application of SIT in agricultural pest management.