The Department of Agriculture and Food’s trial release of sterile fruit flies around Roleystone has finished and provided some useful lessons.
Department senior research officer Bill Woods said the trial examined whether treating a small buffer area of the town with sterile male flies would give some protection to adjacent orchards from fruit fly incursions.
Sterile fruit flies are reared at department facilities in South Perth and irradiated so they become sterile.
These sterile males are then released into known populations of fruit fly. The wild females who mate with the sterile males will lay only sterile eggs. This is known as the ‘sterile insect technique’ which can be used to help control fruit fly.
“The trial was designed to run for 10 weeks with the last release on 13 December,” Mr Woods said.
“Initial results were promising, though by the trial’s end sterile flies were over-run by wild flies. Many of these were moving in from outside the release area where numbers had bred up on loquats, apricots and citrus.”
Mr Woods said unseasonal summer rain had provided favourable conditions for an increase in fruit fly numbers. The recent extreme temperatures had some temporary impact in lowering fly numbers.
“As evidenced by our monitoring trap catches, sterile flies move up to one kilometre and were often found in traps on the adjacent orchards,” Mr Woods said. “These flies are indistinguishable from wild flies unless looked at under ultraviolet light where fluorescent dye markers can be seen.”
To control fruit flies in Roleystone next season, Mr Woods suggested industry in conjunction with householders needed to apply an area-wide baiting scheme in September and October to reduce flies emerging from the ground to very low levels, before sterile release could be effective.
Such baiting schemes have been successfully managed by local governments in other shires.
“Sterile flies are just one weapon for use against the Mediterranean fruit fly,” Mr Woods said. “It is not a silver bullet. Sustained baiting by commercial growers and surrounding residential areas, plus scrupulous orchard hygiene to remove breeding sites, are essential.
“Trials will begin in Jarrahdale soon testing different fly release techniques, spacing and density. Once we are happy with a technique we can begin releases on larger orchard blocks.”
Media contact: Jodie Thomson, media liaison +61 (0)8 9368 3937