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Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.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, ‘Qfly’ was Australia’s most significant horticultural pest and was a major biosecurity problem. The adults layed their eggs in ripe fruit and the larvae feed on the flesh of the fruit, rendering it unmarketable. The sterile insect technique (SIT) was a form of biological control in which large numbers of sterile flies were used to flood the fly population, reducing the possibility of mating between wild flies and the production of fertile eggs.

In this project, the researcher aimed to develop more effective sterile insect emergence and release technologies to improve the success and cost-effectiveness of sterile Qfly releases. Guidelines for pupal release were developed including optimal pupal loadings and release timings that maximise the emergence and flight activity of sterile adult Qfly. For adult fly releases, the researcher developed a method that maximised emergence success, flight activity, persistence, abundance and mating competitiveness of sterile male flies. Trials using chilled adult flies resulted in the development of a protocol that similarly maximises emergence, flight and longevity. A prototype device for releasing chilled adult flies from a slow moving vehicle was also developed.

Overall, their results showed that significant decreases in wild fly populations could be achieved using any one of the three release methods developed and that a method needed to be chosen dependent upon the location and resources available. This study also demonstrated that, based on trap recapture rates, a lower numbers of mature sterile flies (i.e. protein fed flies) needed to be released to achieve control, relative to releases made using immature flies. Further studies needed to be completed to scientifically verify and establish the absolute number of mature sterile flies required to suppress and/or eradicate a given wild population, to minimise the requirement for sterile flies and thus further reduce costs.

It was recommended that low-level sterile releases were used in towns surrounding the fruit fly exclusion zone (FFEZ) to suppress wild Qfly populations in these areas, thus minimising the pressure placed on the FFEZ. Sterile fly releases also needed to be used to eradicate wild Qfly in the NSW FFEZ, using the strategic release plan and the standard operating procedures developed as part of this study. The SIT also needed to be considered in endemic areas where orchards were geographically isolated, or where control was being attempted on an area-wide basis.