Sex selection genes from fruit fly species for use in SITplus (FF17000)

What was it all about?

From 2018 to 2023, this project acquired the genetic knowledge needed to develop a male-only (genetic sexing strain or GSS) for Queensland fruit fly.

Sterile Insect Technique (SIT) has become a valuable tool to combat seasonal outbreaks of the Queensland fruit fly (Qfly) in Australia. While sterile male Qflies are the active control agent in the field, both sexes are currently released because existing protocols are unable to selectively remove females during breeding.

An international team was assembled to find the genes that enable separation of sexes at pre-adult stages and/or mutations that cause female-specific lethality at high temperatures in other global fruit fly pests and transferred such information to Qfly for validation. This partnership identified the white pupae gene that allows genetic sexing based on pupal colours in three exotic species. This allowed us to target the same wp gene in Qfly to generate equivalent pupal colour mutants by gene editing (CRISPR/Cas9).

The information was promptly fed into a parallel Hort Frontiers Fruit Fly project Breeding a male-only strain of Queensland fruit fly (FF18002), where one pupal colour mutant strain (Greyscale) was generated and subsequently combined with a translocation strain to produce the first GSS for Qfly.

The discovery of wp also expedited the identification of a temperature sensitive lethal (tsl) candidate mutation in the Mediterranean fruit fly (medfly) GSS. If successfully validated in Qfly and incorporated into the GSS, the tsl mutation would further reduce production costs of sterile male Qflies. However, although the researhc team successfully identified the equivalent tsl candidate gene in Qfly, it is distant from the wp gene on chromosome 5 (on different chromosome arms), suggesting that it would not be feasible to directly transfer the same wp-tsl genetic sexing mechanism from medfly to Qfly. 

The findings underscore the need to prioritise tsl candidate genes that are close to the wp gene in Qfly to create a functional wp-tsl GSS. 

This project provided the prerequisite knowledge to facilitate the construction of a Qfly GSS based on pupal colour to reduce the cost of sterile insect production and ultimately, to protect Australian fruit crops and preserve market access.