Mating competitiveness and compatibility of genetically engineered strains of Queensland fruit fly for sterile insect technique

Queensland fruit fly (Q-fly) (Bactrocera tryoni) is the most damaging insect pest of horticulture in Australia. The sterile insect technique (SIT) provides an effective, species-specific, and environmentally benign method for regional management of Q-fly outbreaks. Genetically engineered strains have recently been developed (1) to enable male-only releases through sorting by sex differences in pupal colour (Grey-Scale Exon-3 [GS Exon-3], Genetic Sexing Strain [GSS]) and (2) to enable phenotypic marking through yellow body colour (Yellow-1, Yellow-2). The present study assesses field cage mating competitiveness and mating compatibility, and routine quality control parameters, of these engineered strains, comparing them with the unengineered laboratory strain that is currently used in SIT programs. GS Exon-3, GSS, and Yellow-1 strains performed as well as, or better than, the unengineered strain in mating competitiveness, mating compatibility, copula latency, copula duration, and indices of sexual isolation when paired with both wild and laboratory flies, as well as for emergence, flight ability, and egg hatch rate for all except GSS, which had reduced egg hatch rate. However, Yellow-2 had lower mating performance, percentage of emergence, flight ability, and hatch rate, indicating lower suitability for SIT programs. These results support continued investigation of GSS and Yellow-1 as promising candidates for deployment in SIT programs, offering potential improvements in cost-effectiveness, operational safety, and efficiency through male-only release or phenotypic marking.