The fruit was certified as treated fruit and was sold in a Tasmanian supermarket.

Ms Courtney said the government was “very concerned” about the incident.

The North-East is under an enforced fruit fly control zone after a fly was found at George Town in February.

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“The fruit, which transited through Victoria to Tasmania, was certified treated and so we are naturally very concerned how this has happened,” she said.

Ms Courtney has met with the TFGA and Fruit Growers Tasmania on the issue.

​“The Tasmanian Government is determined to eradicate fruit fly from this state,” she said.

“It is important to recognise that no fruit flies have been detected outside of the two control areas.”

There are more than 1000 fruit fly traps being monitored all around Tasmania.

“All matters around the larvae discovery in the grapefruit are still being actively investigated.”

Biosecurity Tasmania general manager Lloyd Klumpp said the detection of fruit fly larvae in Hobart ‘was not unusual’ and said Tasmania gets “two or three close calls” a year.

He said the detection did not warrant an extension of the fruit fly control zones already in place.

An exclusion zone is set up in the North-West from Ulverstone to Port Sorell and as far south as Sheffield.  A second exclusion zone has been set up to include Beaconsfield, Beauty Point and George Town.

However Mr Klumpp said the detection of fruit fly larvae in southern Tasmania did not warrant extension of the control zones.

“It is not unusual for us to see flies, we get two or three of these every year; it’s rare but not unusual.”

Mr Klumpp said the event showed the national biosecurity response to fruit fly was “under pressure.”

“No system is perfect, there will always be some form of leakage but the whole event demonstrates the national system is under pressure,” he said.