Breeding a male-only strain of Queensland fruit fly (FF18002)

What was it all about?

From 2019 to 2023, this project worked to develop a male-selecting strain of Queensland fruit fly for use in the Port Augusta SITplus facility.

Sterile Insect Technique (SIT) involves the release of large number of sterile males into the outbreak areas to mate with wild flies and the sterility of the males then prevent the wild females from producing the next generation of flies. The national Qfly SIT program at present involves the release of both sterile male and females as there is no efficient way of separating and removing the females prior to release, but it is only the sterile males that are useful for the SIT control of outbreak flies. Hence having a sexing strain that allows for the separation of males and females in SIT facilities could reduce the cost of rearing the unwanted factory females for release purposes and at the same time improve SIT efficiency.

This project has produced various genetic strains for consideration of use in the SIT program. These strains were mainly generated using the CRISPR/Cas gene editing technology to induce or introduce mutations but not all strains are considered genetically modified (GM). One of the strains is a pupal colour genetic sexing strain (Greyscale GSS) that consist of males with normal brown pupal colour and females with greyscale (a range of white to grey) pupal colour. Greyscale GSS allows males and females to be separated by colour at the pupal stage, which could be done by mechanical means, thus facilitating the removal of females prior to release – in essence, a male-only strain. This strain is the first pupal GSS and the only GSS in existence for Qfly.

This work has also produced two temperature sensitive strains, with data showing embryonic lethality to varying levels at high heat temperature, such as 33 degrees celsius and above. Adults were observed to show a paralysis phenotype at high temperatures. These strains are currently the only temperature sensitive strains in existence for Qfly and could be used in further development to produce a temperature sensitive GSS (in which females are temperature sensitive and can be eliminated by heat treatment whilst males are similar to wild flies), ideally combined with the pupal colour GSS.

Marker strains have been developed, which can enable easy identification of the flies. The most promising marker strain is the yellow strain, in which flies have yellow body and wing colours that are distinguishable by eye and its identity can also be confirmed by simple molecular methods. If used as a factory strain, the yellow marker can replace or be used in conjunction with the current methods (dye and isotope analyses) employed to identify if flies caught in traps are from the factory or are wild flies, which will subsequently inform area-wide management strategies.