Fly sterilisation program fruitful

Fifty tonnes of flaky bran, 25 tonnes of sugar, 12 tonnes of yeast and 150,000 litres of water add up to 1.5 billion Mediterranean fruit flies (Medfly).

The impressive tally is a result of a 10-year operation by specialised facilities at the Department of Agriculture and Food WA (DAFWA), which uses sterile insects to control fruit fly populations.

Medfly is a serious fruit pest and can infest a wide variety of fruit and vegetable crops.

Department senior research officer Bill Woods said the fruit flies reared at the facility were irradiated so they became sterile and special breeding techniques were used so only males were produced.

"These sterile males are then released into known populations of Medfly," he said.

"The wild females who mate with the sterile males will lay only sterile eggs. This is known as the 'sterile insect technique' which is used to control, and in some cases eradicate, outbreaks of Medfly."

The male Medfly are grown on an artificial diet of bran sugar and yeast. The bulk of sterile flies are sent to South Australia as part of a successful collaboration with the Department of Primary Industries and Regions in SA.

"Flies are produced at South Perth, sterilised at the pupa stage and then air-freighted overnight to Adelaide," Mr Woods said.

"The consignments are picked up from the airport the following morning. The pupae are placed into containers in special rearing rooms, emerge as winged adult flies and then released throughout the area where a fruit fly outbreak has been found.

"The process is repeated usually over several months until the outbreak has been eradicated."

The collaboration resulted in the eradication of seven outbreaks from SA and the continued improvement of the eradication process which now uses an organic bait for a short period followed by release of sterile flies.

The maintenance of fruit fly area freedom in SA allows fruit to be grown without fruit fly damage while commercial producers can access lucrative overseas markets without having to disinfest the fruit.