Designer perfumes for fly-ridden cows

By Lila Guterman CATTLE may use more that just a flick of their tails to shoo flies away. Scientists have isolated chemicals from cows that alter flies’ behaviour, and they say the discovery could reduce the need for insecticides. When flies feed on cows they stress the animals, reducing growth and milk production. The insects also carry diseases. Cattle farmers rely on synthetic insecticides to protect their herds from flies, but researchers are keen to find more environmentally friendly options. Some cows attract far more flies than others, something that scientists had put down to differences in their smells. Michael Birkett of the Institute of Arable Crops Research in Rothamsted and an international team of colleagues set out to test the idea and discover which chemicals are responsible. The team isolated 18 chemicals that cows secrete or exhale, and which stimulate nerves in flies. They have tested the effects of one of these chemicals in the field by putting it in slow-release bags, and placing the bags on the two cows in a herd of six that attracted flies most. The number of flies evened out among the cows, Birkett told the International Congress of Pesticide Chemistry in London last week. This suggests that the chemical repelled the insects. According to Bradley Mullens, an entomologist at the University of California, Riverside, it is the first time natural products have been shown to influence fly behaviour in this way. “I think it’s very exciting work,
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