Fly in the ointment?
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| credit: Brian Barnes, ARC |
The Western Cape is one of the most beautiful and productive parts of South Africa, an area famous for the quality of its wines and fruit, which fetch high prices overseas. However, wealthy shoppers demand a high quality product: only healthy grapes with perfect skin are acceptable in their table fruit bowls. And, while the Western Cape enjoys incredible scenery, it is also home to two species of fruit fly, which are only too happy to get in the export 'ointment'. Adult fruit flies are, as their name suggests, just as partial to the juicy fruit of the Western Cape as human consumers. Piercing the fruit to lay eggs, they leave unsightly blemishes that, with further decay, render the fruit unacceptable for supermarket aisles. The insects also use fruit as both incubator and larval food source.
The damage done has several consequences. First, the actual amount of fruit that can be harvested is obviously reduced, which is unfortunate not only for exporters, but also for the local people, who depend on fruit as an important food source. Fruit flies are international quarantine pests, so their presence also limits the export market, since countries free of the pest, including the USA and Japan, are reluctant to import from fruit fly affected regions. Moreover, conventional pesticide treatments to limit the damage are expensive, further cutting into growers' profits, and are disruptive to the environment.
In 1999 New Agriculturist reported on a Sterile Insect Technique (SIT) project, that was just getting underway in the Hex River valley of the Western Cape. The project has been run by an institute of South Africa's Agricultural Research Council (ARC), Infruitec-Nietvoorbij in Stellenbosch, and given substantial financial and technical support by the FAO/IAEA Joint Division. But considerable financing has come from the growers themselves, who agreed to pay a levy of ten cents on every export carton of fruit and, in the first two years, they have raised one million South African Rand, enough to meet the operating costs of the project. The growers buy sterile male flies from the ARC's fly rearing facility and twice a week hire a plane to release them into the valley. Monitors are also employed to provide up to date information on the success of the growers' investment. The production of the sterile males is funded by a unique Partnership between the ARC and the Deciduous Fruit Producers' Trust.
So far the outlay has proved worthwhile. Sterile male fruit flies have now been released for two seasons, and the results are already impressive. Numbers of flies are significantly lower (see graph), and this season the number of cartons rejected for export because of fruit fly damage has halved from 8% to 4%, the lowest it has ever been. In addition, growers estimate that in the last twelve months using SIT has cost them R2 million less than conventional pest control methods, thus more than recouping their R1 million investment. Moreover, in contrast to chemical applications, SIT is harmless to the environment, and the harvested fruit can be sold with reduced chemical residues. In recognition of this success, the Western Cape government has recently allocated R1.5 million to the project, and released a statement emphasising the importance of the technique to agriculture in the province.
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Wild flies trapped in Hex Valley 1997 - 2001
(2001: up to week 19) |
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Although cost-effective and ecologically-compatible fruit fly control is the immediate goal with SIT, the vision of the ARC team is to make the whole of the Western Cape fruit fly free, and to make their laboratory a centre of excellence in Africa for the SIT technology, thereby helping to spread SIT further afield to other fruit growing areas in countries further north. There is also a good possibility of using SIT to control or eradicate other fruit pests, and also tsetse fly, in the sub-region. Current limitations to their ambitions would appear to lie principally in the availability both of funding and trained scientists to learn and further develop this high tech approach.
For further information contact: Brian Barnes, Sterile Insect Technique Division, ARC Infruitec-Nietvoorbij, South Africa
