A third season of sterile Queensland fruit fly (Qfly) releases have commenced across Cobram, Victoria and Hillston, NSW.

Conducted as part of the Hort Innovation funded Post Factory Pilot of SITPlus Fly Production Project, the releases are the final in a series to develop, establish and refine the operational release aspects of the Qfly sterile insect technique (SIT).

The trial has been led by Macquarie University and provides an evaluation of the effects of SIT when employed in urban areas.

Dr Bishwo Mainali of Macquarie University said the weekly releases of two million flies as part of the research trial, had greatly depressed the local Qfly population compared to comparative control sites.

“This has been especially evident in Cobram over the previous two seasons, a great outcome given the Qfly pressures experienced across the eastern and southern states over the past year.

“Over its duration the project has seen the incorporation of a range of incremental improvements such as the use of gel-based diets, improved pre-release holding times and improved identification methods,” Dr Mainali said.

Macquarie University industry liaison and outreach coordinator, Chris O’Connor said these gains had contributed to vastly improved efficiency, lower costs, greater efficacy, and a SIT program which is being noticed internationally.

The Goulburn Murray Valley (GMV) fruit fly area wide management program supports the SIT trial in Cobram through creating awareness, education and engagement in the community, industry and government. The program is funded by the Victorian Government’s Managing Fruit Fly Regional Grants Program.

Goulburn Murray Valley fruit fly area wide management program coordinator Ross Abberfield said program support includes the establishment, monitoring and research of three separate Qfly trapping grids targeting rural, urban and SIT sites in the Goulburn Murray Valley.

“The program’s SIT trapping grid in Cobram monitors sterile Qfly activity within 1km, 2km and 5km radii of the aerial release zone,” Mr Abberfield said.

Sterile and wild Qflies are separated and growers in the vicinity are advised of actual wild Qfly numbers to avoid reacting to false positives in their traps. Other features of the area wide management program include the removal of more than 100,000 unmanaged or unwanted host trees which provide potential breeding habitat for fruit fly, along with the efforts of a large base of community volunteers actively educating the community how best to reduce Qfly numbers in the region.

Horticultural entomologist Andrew Jessup is responsible for analysing the program’s trapping data which is used as the basis to inform the community and industry through monthly Qfly updates in all newspapers throughout the GMV.

“Data from 33 traps in the urban area of Cobram were compared with data from about 370 traps dispersed over the rest of the GMV region. Results showed that since the start of SIT releases in September 2019, the relative trap capture rates declined in Cobram when compared with the rest of the GMV.” Mr Jessup said.

The number of Qfly trapped per year (from 1 July to 30 June) in Cobram declined from 22.7% of the total number of Qfly trapped in the GMV in the year to 30 June 2018 (where no SIT was applied) to only 3% in the year to 30 June 2021 (the end of the second year of SIT).

The figures for Shepparton were 9% to 30 June 2018 to 13% to 30 June 2021 and for Mooroopna: 4.9% and 6.5% respectively. This data shows Qfly populations in Cobram declined with SIT while those of other towns without SIT increased.

The reduction in severity of Qfly in Cobram since the spring of 2019 is most likely to be due to a combination of SIT and area wide management strategies that are also in place in Cobram.

It is anticipated that data from the third SIT releases will be used to extract the impacts of SIT alone and area wide management alone on Qfly populations.

“There is no doubt that SIT, in combination with area wide management, has resulted in reductions in Qfly trap capture rates in Cobram after only two years of releases,” Mr Jessup said.