SCIENTISTS at the CSIRO, Australia's national research organisation, this week released the pupae of genetically manipulated blowfly en masse on the Furneaux Islands, a remote group of islands north of Tasmania. The release is part of a long-term experiment to combat a disease called fly strike which can kill sheep. Over the next two years, the scientists will release more than 400 million pupae, which each take about two days to turn into flies.
The female sheep blowfly (Lucilia cuprina) causes fly strike when it lays eggs in areas of the sheep's fleece close to infected sores. Maggots feed on the sores and enlarge the wounds. In Australia, sheep farmers lose up to A$250 million (Pounds sterling 125 million) a year because of the disease. Meat production suffers and the wool fibre weakens, reducing the value of the fleece. Untreated sheep die.
The sheep blowfly is now resistant to various insecticides with which farmers have controlled it in the past. Scientists from the division of entomology at the CSIRO have reared a strain of male sheep blowfly that is both partially sterile and contains mutant genes that confer blindness on their female descendants. A rearrangement of the chromosome which confers maleness causes the sterility. The scientists will release 3 million males this week, and about 7 million a week by January. 'We want to overwhelm the local fly population,' said Geoffrey Foster from the CSIRO.
If the partially sterile males mate with a wild female, only 45 per cent of her eggs will hatch. The female line also carries the mutant gene that will cause white eye and yellow eye in future generations. Females with this condition cannot find food and fall prey to predators.
The experiment on the Furneaux Islands will cover 2000 square kilometres, an area about 50 times as large as that used for any previous release. After about 15 generations, the scientists hope to eradicate the fly from the islands.
Eventually Foster and the project leader, Rod Mahon, hope to release pupae of the flies on Tasmania and on parts of the Australian mainland. Agriculture departments in New Zealand have also shown interest in the work. Another goal is to release adult flies from aircraft. At present, scientists release pupae from ground stations. The pupae become adult within about two days.
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