Disruption of duplicated yellow genes in Bactrocera tryoni modifies pigmentation colouration and impacts behaviour

Irradiated Queensland fruit flies (Bactrocera tryoni) used in Sterile Insect Technique (SIT) programmes are marked with fluorescent dyes to distinguish them from wild flies when recaptured in monitoring traps. However, coating sterile pupae with powdered dyes can reduce emergence rates and fly quality and can sometimes produce insufficiently certain discrimination through inadequate coating or because the dye is transferred to wild flies through contact. Here we created a phenotypically distinct B. tryoni strain that lacks typical melanisation patterns through CRISPR/Cas9-mediated mutagenesis of tandemly duplicated yellow-y genes and then assessed effects of this visible trait on fly performance. Recessive mutations are only required in one of these copies to restrict melanisation and generate a phenotype clearly distinguished from wild type. The yellow strain showed significant declines in eclosion rates and in the percentage of fliers directly after emergence. Locomotor activity was greater in the yellow strain, and these mutations did not generally affect mating probability, copula latency, or copula duration. The longevity of yellow flies was approximately 10 days shorter than wild-type flies in both sexes. Overall, replacing dyes with yellow body marker for SIT can simplify production, eliminate a step that is known to reduce fly quality, remove potentially hazardous dyes from production, enable accurate discrimination from wild flies, and improve cost-effectiveness; however, direct comparisons of the decrements in performance associated with dyes on mass-reared wild-type flies and disruption of yellow-y genes are now required to determine the relative suitability of these marking methods for B. tryoni SIT.