Q-fly don’t bother me: SA releases 1 billion sterile fruit flies

South Australia has now dispersed 1 billion sterile Queensland fruit flies into its Riverland fruit-growing region in response to an outbreak of the destructive citrus pest.

Bactrocera tryoni is commonly referred to as Queensland fruit fly or ‘Q-fly’ and is found across Australia’s northern tropics and east coast. It is less commonly found in South Australia and Western Australia, though outbreaks have been known to occur.

South Australia has strict biosecurity laws and polices the importation of certain fresh food products from outside its borders. The state’s citrus-growing Riverland region bordering the Murray River is experiencing 47 Q-fly outbreaks.

Queensland fruit fly on a leaf
A Queensland fruit fly. Credit: Chloe Johnson / PIRSA.

To combat this, the state’s 8-year-old Sterile Insect Technology facility based in Port Augusta has now neutered and released 1 billion male fruit flies into the region. This process will continue until mid-February with around 40 million sterile files being reared each week.

A case of X-ray extermination

As with other efforts to eradicate pest species, the premise of insect sterilisation is to introduce numerous individuals of a target species that can’t produce viable offspring.

The aim is for sterile males to outnumber their wild counterparts. By mating with wild females, the populations of Q-fly, which have short lifespans of under 2 months, should rapidly decrease.

The sterilisation process is one of the final steps used by agricultural authorities when rearing its candidate males, whereby eggs collected in a secure facility are left to hatch into larvae (or maggots) on special tray towers, where they will feed for about a week.

They are then harvested and bagged with vermiculite to provide a medium where the maggots harden their skin and transition into their pupal form.

In these dark-coloured, hardened stages, the pupae are separated from the vermiculite medium and exposed to X-rays to sterilise them before being shipped out to hatch and distributed in the environment.

South Australia’s Department of Primary Industries and Regions (PIRSA) is responsible for the state’s sterile fly program and anticipates continuing the release of these specimens until mid-February. PIRSA estimates the outbreak will end on 20 March.

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