Sterile male fruit fly pupae are being stockpiled in South Australia (SA) in anticipation of damaging outbreaks of the fruit pest this summer.

Last summer, SA spent more than A$1m (US$500,000) on chemical sprays to control the pest (known as the medfly), but now authorities are paying the Agriculture Department A$2000 per million flies and aiming to buy five million every week.

The flies are bred at a facility in South Perth, and are a useful tool because of their gender-lined gene. Scientists have found that by manipulating the temperature of the breeding unit, 99.9% of the females were killed, and releasing sterile males into the wild has a disastrous effect on the breeding cycle of medflies.

This summer will be the first time the method has been employed in South Australia, but it is regularly used in Western Australia (WA) and overseas.

The fly, which attacks stone, citrus and pome fruits, was estimated to cost WA A$3.8m every year in lost production and other control methods.

In the US meanwhile, San Francisco authorities release 300m sterile medflies every week to protect the Californian fruit industry.