Towards developing a male-only Queensland fruit fly strain (HG02037)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

The Queensland fruit fly or Q-fly, Bactrocera tryoni, had been regarded as the most serious pest of horticulture in NSW and Queensland for many years. In spite of interstate quarantine measures (bait-spraying, trapping, exclusion zones, monitoring grids and quarantine policing), isolated outbreaks had occurred in Victoria, South Australia and Western Australia, a resident population had become established in Alice Springs and resident populations also existed in a number of inland towns around the Fruit Fly Exclusion Zone (FFEZ). The pre-harvest control methods used at the time for Q-fly relied heavily on cover sprays, containing one of the systemic broad-spectrum insecticides which also destroyed important beneficial insects of the orchard.

The Sterile Insect Technique (SIT) was a biological control method which had been widely adopted by industry to minimise the amount of chemical spraying. In this method, huge numbers of insects were reared, sterilised and released to mate with the wild insect pests, so that wild females produced no offspring and pest numbers were dramatically reduced. Overseas work on the related pest species, Med-fly, had shown that SIT was both cheaper and more reliable when sterile males only were released, rather than sterile flies of both sexes. Thus there was a demand from the horticultural industries for research to develop a male-only strain for Q-fly.

Because Australia was surrounded by countries which contained endemic fruit fly species with an invasive pest status even greater than that of Q-fly, there was a need to develop male-only SIT systems that could be readily transferred to other species. The use of gene constructs that kill females in a fly-rearing factory would provide the best outcomes for transfer between species in the future.

This project had provided an investigation of sex-specific genes that might be used in female-killing constructs in Q-fly and related pest species, such as Oriental fruit fly. It had shown that the female-specific Yolk protein genes could not be as readily adopted as the sex-determination gene doublesex. Accordingly, a set of constructs had been made using control regions of doublesex, with a cell-death gene grim, which should function to kill female flies early in their development in the SIT facility.

Future R&D required the further development of stable, reliable genetic transformation systems for Q-fly, and a testing of the doublesex constructs for their efficacy in killing female embryos. A comparative investigation of other sex-determination genes in Q-fly, for their utility in male-only SIT would also be productive at this stage of research.