An outbreak of Queensland fruit flies has been declared in Adelaide by Biosecurity SA.

A 1.5 kilometre quarantine zone has been established around the affected area in West Croydon and an eradication program is about to start.

State Minister for Agriculture, Food and Fisheries Leon Bignell said staff will begin a bait-spotting program together with a hygiene regime aimed at eliminating any fruit flies from the outbreak area and nearby surrounds.

"We will have staff in the area first thing on Boxing Day morning in response to this threat," Mr Bignell said.

"Residents and businesses within the quarantine zone will shortly be receiving information from Biosecurity SA about the outbreak detailing what part they can play in preventing its spread."

Mr Bignell said fruit flies do not normally exist in South Australia, and must have been brought into the state from infested fruit originating in one of the eastern states.

"Fortunately, the householder who discovered the fruit fly larvae rang the Fruit Fly Hotline to report what they'd found in their backyard fruit," Mr Bignell said.

"Early reporting of fruit fly discoveries is vital in aiding successful eradication.

"I urge everyone to be just as vigilant and report if they discover any maggots, and to reduce the risk of fruit fly breeding by not leaving ripe fruit lying on the ground in backyard gardens."

Mr Bignell said residents and businesses inside the quarantine area could help eliminate fruit flies by practicing a few simple measures including not giving away any fruit, not leaving fruit or vegetables lying on the ground, and not composting any fruit or fruiting vegetables, including those purchased from a shop.