The goal of this project is to create new temperature-sensitive and yellow marker strains that are more genetically stable and easier to scale for SIT programs

The University of California, San Diego has been awarded $209,300 under a Cooperative Agreement from the Animal and Plant Health Inspection Service (APHIS) to develop improved genetic strains for Sterile Insect Technique (SIT) programs targeting Mediterranean fruit flies (medflies) and Mexican fruit flies (mexflies). The project, which commenced September 30, 2025, and concludes September 29, 2026, is funded under the Plant and Animal Disease, Pest Control, and Animal Care program (CFDA 10.025). The primary deliverables include optimized genetic constructs for temperature-sensitive and yellow marker-based sex-sorting systems that will improve the genetic stability, scalability, and field performance of fruit fly strains used in SIT pest suppression programs.

The research leverages sex-specific introns to disrupt temperature-sensitive lethality (TSL) and yellow marker genes, creating more genetically stable strains with reduced recombination rates and improved male fitness characteristics. By standardizing the long-term performance of temperature-sensitive mutant lines across laboratories and generating female-specific yellow strains, the project aims to reduce phenotypic variability and enhance fly production efficiency. These enhanced genetic tools are expected to positively impact both medfly and mexfly SIT programs by improving scalability of production and field performance while supporting the broader agricultural mission of protecting U.S. crops from economically injurious fruit fly pests.

Our approach uses SEX-specific introns to disrupt TSL and yellow to generate temperature-sensitive and yellow marker systems in the medfly and mexfly that can be used to easily identify and remove females in SIT programs. Our previous work has focused on the development of new genetic sterilizing technologies and the development of SEX-specific fluorescent markers in the medfly and mexfly. This work has allowed US to develop separate CAS9 lines and grna constructs that can be modified to support the development of these systems. The SEX-specific TRA introns proposed to generate SEX-specific expression of TSL and yellow have been validated in the medfly separator system. The benefit that this project offers is we can improve the stability and fitness of TSL and yellow fly strains. We will generate TE mperature-sensitive mutant lines that are less prone to recombination, thereby standardizing their long term performance between laboratories and reducing the variability in their temperature-sensitive phenotype. In the current GSS yellow strains, the males have the yellow phenotype, which causes fitness issues that impact their production and performance in the field. We will generate female-specific yellow strains, which should improve male fitness. These tools have the potential to positively impact the medfly and mexfly SIT programs by improving the scalability of fly production and field fitness. We will deliver optimized genetic constructs for the generation of mexican fruit fly and mediterranean fruit fly strains carrying a yellow marker-based SEX sorting system and a temperature-specific SEX separation system. This approach has the potential to positively impact the suppression of mexican fruit fly pests as well as other SIT programs.