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SITplus sets Australia up for Queensland fruit fly suppression

Pest and Disease Management

Sterile insect technique (SIT) involves developing and mass-rearing sterile fruit flies, which are then released into Queensland fruit fly (Qfly) outbreak areas in large numbers to mate with wild flies, preventing wild females from producing the next generation of flies.

Latest research results from large-scale aerial release trials of millions of sterile Qfly across Cobram, Victoria, show Qfly numbers were suppressed for entire seasons, over three successive seasons. The trial releases were part of the Post factory pilot of SITplus fly production (FF17001) project.

While project leaders are analysing the project’s data, its success is among the many groundbreaking results being achieved by the Hort Frontiers Fruit Fly Fund and its SITplus initiative to control this costly pest and ultimately protect Australian fruit crops and preserve market access.

Hort Innovation Head of Biosecurity R&D, Dr Greg Chandler, said the research and development (R&D) projects which SITplus has invested in have collectively created one of the most advanced SIT programs in the world and have set up Australia for effective Qfly suppression.

“We’re now focusing on producing sterile male-only lines so we can make SIT a cost-effective tool for large-scale Qfly suppression. We’re also looking at how beneficial organisms, including viruses, can be used in conjunction with SIT,” Greg said.

“Viruses of fruit flies have been severely understudied and one of the projects funded by Hort Innovation – SITplus: Port Augusta Qfly SIT factory pilot operation (FF18003) – will more than double the known number of scientific publications.

“Studies so far indicate that Qflies have a large diversity of RNA viruses that co-occur within the one fly and that these patterns are relatively geographically distinct, and that they have an impact on Qfly fitness, particularly under stressful conditions.

“Future focus areas could include investigating releasing SIT Qflies and beneficial insects simultaneously, combining smart traps and SIT for population monitoring, and optimising release methods and timings to reduce costs but maintain effectiveness.”

Sterile Qflies mass reared at the purpose-built SIT fly factory at Port Augusta in South Australia.
Photo: Hort Innovation

Why male Qflies are the focus

While sterile male Qflies are the active control agent in the field, both sexes have been released in Qfly SIT trials to date because there was no efficient way of separating and removing the females prior to release.

To reduce the cost of rearing unwanted females for release purposes and to improve SIT efficiency, a genetic sexing strain or GSS that allows for the separation of males and females in SIT facilities has been developed.

Under the Sex selection genes from fruit fly species for use in SITplus (FF17000) project, a GSS for Qfly at the pupal stage has been developed, which will allow sorting so that only males are released in the future.

Greg said a separate project, Breeding a male-only strain of Queensland fruit fly (FF18002), has also produced various genetic strains that could be used in the SIT program.

“One of the strains is a pupal colour genetic sexing strain that consists of males with normal brown pupal colour and females with greyscale (a range of white to grey) pupal colour,” Greg said.

Greyscale GSS allows males and females to be separated by colour at the pupal stage, which could be done by mechanical means, enabling the removal of females prior to release. This strain is the first pupal GSS and the only GSS in existence for Qfly.

“This work has also produced two temperature-sensitive strains that could potentially be used to eliminate female Qflies by heat treatment.

“The SITplus investment has also produced a genetic yellow-colour strain of Qfly that makes them highly distinguishable from wild Qflies. This will eliminate the need to dye the sterile flies for identification purposes before they’re released.

“It will help identify if flies caught in traps are sterile flies or wild flies, which will subsequently inform area-wide management strategies. This also benefits international trade, as sterile flies will be readily distinguishable from wild flies by non-experts.”

Tackling other horticultural pests

When the SITplus program was established in 2014, the technological state of Qfly SIT lagged years, or even decades, behind overseas SIT programs. As the SITplus program developed, there was increasing awareness of just how little was known about the basic biology of Qfly in relation to traits of importance for SIT, and also of some basic aspects of SIT operations.

The establishment of the SITplus: Raising Qfly sterile insect technique to world standard (HG14033) program set out to address a wide diversity of knowledge and technology gaps, and to as quickly as possible close the gap between the research underpinnings of Qfly SIT and overseas programs of other species.

Greg said it has supported very significant advances in Qfly SIT, not only closing the gap to overseas programs but advancing Qfly SIT to a world-leading position.

“To ensure that the research findings are of high standard, and are available to future researchers, managers and trade negotiators, the large majority of completed work is in, or is intended for, international peer-reviewed scientific literature.

“The world-leading R&D that SITplus has invested in and the SITplus production facility have the potential to be extended to SIT research into other major horticultural pests, such as codling moth. We have our eye on Qfly at the moment, but the technology is applicable to other pests in producing multiple SIT species in the same facility.

“The advances made in the understanding of Qfly ecology, behaviour and genetics provides a world-leading resource for the development of future innovations in SIT and other sustainable management tools.

“It has also made significant contributions to training and supporting the next generation of insect biosecurity researchers.”

Apple and pear growers interested in finding out more about SIT and SIT Qfly availability can contact Ian Cover, APAL Industry Services Manager – Biosecurity and Extension, at [email protected].

 

SITplus production facility

The world-leading R&D that SITplus has invested in and the SITplus production facility have the potential to be extended to SIT research into other major horticultural pests, such as codling moth. Photo: Hort Innovation

Sterile Qflies are mass reared at the purpose-built SIT fly factory at Port Augusta in South Australia, first established in 2016.

Greg said the facility is refining procedures to ensure the highest possible number of fit for purpose, healthy Qfly are produced in the most financially economical way.

From 2019, the factory has consistently produced up to 25 million sterile pupae per week.

Some of these sterile pupae were dispatched to rear out centres in Yanco, NSW, and Tatura, Victoria, for experimental release efforts as part of the Sex selection genes from fruit fly species for use in SITplus project. Others were dispatched to the Queensland Department of Agriculture and Fisheries to assess efficacy of IR colour pupal sorting equipment under the Sex determination of fruit fly pupa using near-infrared spectroscopy project, and to the South Australian Research and Development Institute (SARDI) in Adelaide for insecticidal bait efficacy trials.

Many hundreds of millions of sterile flies were also dispatched to rear out centres in Netley and Renmark in South Australia for use in outbreak responses in both metropolitan Adelaide and in the Riverland, as well as to assist outbreak response in Perth, WA.

 

SITplus projects mentioned in this article include:

  • Sex selection genes from fruit fly species for use in SITplus (FF17000)
  • Post-factory pilot SITplus fly production (FF17001)
  • Breeding a male-only strain of Queensland fruit fly (FF18002)
  • SITplus: Port Augusta Qfly SIT factory pilot operation (FF18003)
  • Sex determination of fruit fly pupa using near-infrared spectroscopy (FF19000)
  • SITplus: Raising Qfly sterile insect technique to world standard (HG14033)

Find out more information by visiting Hort Frontiers strategic partnerships initiative/Fruit Fly Fund.

 

Read more:

Sterile Insect Technique (SIT) Plus program fact sheet

Sterile flies, sexual development and the surprising role of caffeine in Qfly control (AFG, Autumn 2020)

Male-only gender bias to ramp up Qfly fight (May 2019)

Acknowledgement

Hort Innovation is one of the founding partners of SITplus, with collaborators including Macquarie University, Western Sydney University, CSIRO, Primary Industries and Regions South Australia (PIRSA), the South Australian Research and Development Institute (SARDI), the NSW Department of Primary Industries, Agriculture Victoria, Plant & Food Research New Zealand, and Biosecurity Tasmania.

This article was first published in the Summer 2023/4 edition of AFG.

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