Zapping fruit flies to help combat outbreaks
Find out how sterile fruit flies play their part in the big picture of keeping South Australia fruit fly free.
X-rays and fluorescent dyes don’t usually come to mind when you think of the destructive horticultural pest, Queensland fruit fly, but they are an essential part of the sterile insect technique process to ensure the successful eradication of an outbreak.
The Sterile Insect Technology (SIT) facility at Port Augusta, 300 km north-west of Adelaide, South Australia, has been up and running for three years now and is capable of producing up to 50 million sterile fruit flies each week. Sterile flies are used to combat fruit fly outbreaks and to reduce the pest’s impact in fruit fly endemic regions in Victoria and New South Wales.
Hort Innovation SITplus Program Director Dan Ryan said that the process for mass producing sterile fruit flies was very involved.
Firstly, eggs are collected and placed onto a gel diet to hatch and grow,” he said.
“Once the developing larvae have grown large enough, they jump out of the trays and are collected and placed into bags to pupate.
“Once the pupae are old enough, they are coated with a powdered fluorescent dye which transfers to adult flies as they emerge from the pupae. This dye allows sterile flies to be identified easily when caught in the wild.
“The final part of the process is the most important – the x-rays – where the pupa are exposed to a very high dose of radiation, making them sterile – stopping the emerging adults from being able to reproduce.”
In the event of a fruit fly outbreak, response teams undertake extensive baiting and hygiene programs, including collecting any fallen host fruit in the area. Coupling these traditional techniques with sterile fly releases helps ensure complete eradication of the pest.
Once the baiting and trapping program has been completed, the sterile flies are chilled and loaded into a small plane or vehicle, ready for release in the outbreak area. Remaining wild flies are outnumbered by the sterile flies, so are more likely to mate with the introduced sterile flies, resulting in either infertile eggs or no eggs at all, and so the population crashes.
Primary Industries and Regions SA (PIRSA) Biosecurity SA Manager Plant Health Operations Nick Secomb said using SIT was an invaluable tool in combatting fruit fly and keeping South Australia free from the pest.
“South Australia is the only mainland Australian state that is fruit fly free, meaning we can eat our home grown fruit and vegetables with the assurance they are free of fruit fly,” he said.
“In 2017–18 the estimated farmgate value of the state’s horticultural produce vulnerable to fruit fly was $1.2 billion.”
“The National SIT facility has been a game changer for fighting fruit fly. It has been successfully used in previous outbreaks and will continue to be a key component of our response to protect our vital horticultural sector against this destructive pest.”
The SIT facility is supported by SITplus™, a national strategic research and development program.
The SITplus™ program is led by Hort Innovation, in partnership with PIRSA, Agriculture Victoria, CSIRO, Plant and Food Research, NSW Department of Primary Industries, Biosecurity Tasmania, Western Sydney University and Macquarie University.