The present procedures for prevention, detection and eradication of fruit flies are the result of fifty years experience and development of operational techniques suitable for South Australia. At present some 60 staff are employed by the South Australian Government to keep the state free of fruit fly, plus 12 additional staff employed for the duration of each outbreak.
Partnership with the community
The success of fruit fly operations in South Australia is possible only by the support and co-operation of the citizens of South Australia. In the past fifty years, a partnership has developed between the community and government fruit fly operations, in which householders and commercial fruit growers have seen the benefits of producing fruit without the risk of fruit fly damage and have accepted fruit fly control as a community responsibility. In particular, the voluntary reporting by householders of larvae in fruit, and the acceptance by owners of fruit fly operations on their property have allowed the South Australian Government to sustain fruit fly operations.
The Government maintains a community awareness program through a publicity program. There has also been an education program aimed at school children, which has resulted in a generation of fruit fly aware South Australians.
Private vehicles continue to be the main means of by which fruit fly larvae in host fruits are carried into South Australia from fruit fly epidemic areas on both the east and west coast regions of Australia. South Australia presently maintains four roadblocks on the “high risk” routes into the state. Roadblocks at Yamba on the Shirt Highway between Mildura and Renmark, at Pinnaroo on the Ouyen Highway and at Oodlawirra on the Barrier Highway between Broken Hill and Jamestown intercept road traffic originating from the eastern part of Australia. The roadblock at Ceduna on the Eyre Highway intercepts road traffic from Western Australia. Total roadblock staff is presently 35.
Motorists who fail to declare fruit, vegetables and plant material at these roadblocks are subject to an “On the spot fine” or prosecution.
Commercial shipments of fruit are controlled, and require certification from other state governments that the shipment is free of fruit fly, or has been treated to kill immature stages of fruit flies. A total of four inspectors at South Australian fruit markets and entry points ensure that fruit has been properly treated by checking certifications that accompany the incoming consignments.
Detection of adult fruit flies
The trapping grid throughout the Metropolitan Area of Adelaide now consists of 2,707 sites on a 400 metre grid with each site having two traps, one to detect Queensland fruit fly and the other to detect Mediterranean fruit fly. in addition 67 of these sites also have a methyl-eugenol trap on a 5km grid pattern to detect papaya fruit fly and other fruit flies responding to this lure. Separate trapping grids are in the Riverland, including Mypolonga, with 468 sites, each with three types of traps, on a 400 metre grid throughout townships and a 1km grid throughout the horticultural production area. In addition, Port Augusta, Port Pirie, Whyalla and Ceduna have a total of 316 sites on a 400 metre grid.
These traps are monitored on a weekly basis during the period November to May and fortnightly during the period June to October by a total of ten staff.
A fruit fly outbreak is officially declared by the Chief Inspector appointed under the Fruit and Plant Protection Act, 1992. The Chief Inspector acts on the decision of the Fruit Fly Technical Committee, which presently consists of the Chief Inspector, the Operations Leader, Fruit Fly, the Progam Leader, State Quarantine from the Pest Eradication Unit, and an entomologist from the South Australian Research & Development Institute. The reaction time between detection of an outbreak and the start of eradication operations is usually less than several hours in Adelaide, and less than a day in other areas. The official declaration provides the legal basis for the conduct of fruit fly operations, including the movement of fruit from the outbreak area. For each outbreak, an additional 12 staff are employed for field operations.
Identification of adult flies caught in traps is by comparison with reference specimens and/or by taxonomic key. Larvae of Qfly and Medfly are separated by microscopic characters of the cephalopharangeal skeleton and independently by cellulose acetate electrophoresis of the larval homogenate by specialists at the South Australian Museum. The results of these two methods are available within two hours of submission. As a check, some larvae are cultured in a quarantine insectary, and the identity of the emerged adults confirmed some time after the outbreak is declared.
Present methods of eradication depend on the species of fruit fly. Most outbreaks of Queensland fruit fly are treated with the baiting technique integrated with the release of sterile fruit flies. The integrated Chemical and Sterile fruit fly release Eradication Procedure is conducted in two stages. In the first, two to four bait sprays are applied within a 200 metre radius area (outbreak zone) and one to two applications within a 1.5km radius area (outbreak area) over a one to two week period. The bait is a mixture of protein autolosate and maldison insecticide and is applied in 100mL “spots” to foliage at the rate of 100 spots per hectare (6 to 8 spots per household property). To reduce the mortality among the sterile flies, bait spraying ceases four days prior to commencement of sterile releases. Sterile Qflies bred at a factory operated by the New South Wales Department of Agriculture are released at the rate of one to two million per week over the complete outbreak area for a period of up to ten weeks. These flies are marked with a fluorescent powder to allow them to be distinguished from wild flies caught in traps.
Sometimes, it is not possible to use sterile flies, in which case, baiting is continued twice a week for 6 weeks in the outbreak zone from the last sighting of flies or larvae and then once a week as in the remainder of the outbreak area for a period up to 12 weeks from the last sighting of flies or larvae.
Medfly outbreaks are presently treated by a combination of cover spraying and bait spraying in the outbreak zone and bait spraying only in the remainder of the outbreak area. Three applications of a diluted systemic insecticide (fenthion .086 w/v) are applied to all fruit bearing trees in the outbreak zone at 10 day intervals. The spray kills eggs and larvae within the fruit as well as adult flies sheltering in the foliage.
Whether the outbreak is Qfly or Medfly, fruit is not generally removed from trees as a means of control. At most, host fruit is removed from infested trees and from trees immediately adjacent to the infested tree on the property shortly after the discovery of the outbreak. Fallen fruit in the outbreak zone is also collected weekly, treated with insecticide and deep buried during the program. A ground spray containing chlorpyrifos is applied under known infested tree(s) to kill any larvae or pupa in the soil.