If the shoo fits: cows painted with zebra stripes keep flies in line

https://www.theguardian.com/world/2019/oct/11/if-the-shoo-fits-cows-painted-with-zebra-stripes-keep-flies-in-line

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Painting a cow to look something like a zebra has been found to reduce fly bites by 50%.

Researchers believe painting stripes on to cattle is a world-first and could become an environmentally friendly alternative to pesticides.

The study, published by Japanese scientists in the journal Plos One, found fly attacks were “significantly reduced” by the disguise. The scientists believe the striped pattern confuses the fly’s motion detection and deters the pests.

In what was a five-minute process for each animal, researchers painted white, 4cm to 5cm stripes on six pregnant Japanese black cows. The stripes were drawn freehand, using “commercial waterborne white lacquers” that faded easily.

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The laquered bovines were then observed. Two of the cows were painted with white stripes, two with black stripes and two were left unpainted for a control. The process then repeated so, over nine days, each cow spent three days striped, painted black or unpainted.

Only 55 flies were observed on the zebra cows, compared with 111 on the black-painted cows and 128 on the control cows.

The ersatz zebras were observed to demonstrate only 40 fly-repelling behaviours (such as flicking their tails and shaking their heads) every 30 minutes, compared with 53 and 54 fly-repelling behaviours in the others.

Previous studies have found that flies are less likely to land on horses wearing striped blankets and other objects painted with stripes. But researchers believe this is the first time cattle have been painted and studied in such a way.

“This phenomenon has been explained as modulation brightness or polarized light,” the authors wrote. Previous studies found that stripes confuse a fly’s motion detection, causing them to approach animals at a higher speed, but also to fail to decelerate properly.

The researchers now say more work is needed, both to confirm the link and to develop less labor-intensive ways of ensuring cows remain patterned and zebra-like. If so, it could ease one of the most persistent pest problems that face cattle.

Flies stop cattle from grazing, feeding and sleeping, and can cause “bunching behaviours”, where cattle jostle for space to escape flies, causing heat stress and injury.

“Biting flies are the most damaging arthropod pests of cattle worldwide,” the report said. “The economic impact of biting flies on the United States cattle production was estimated at $2.2bn per year.

“In future the development of more effective techniques to ensure the persistence of black-and white stripes on livestock during the biting fly season (3-4 months) may be necessary.”

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Keith Bayless, a postdoctoral expert in fly biology at Australia’s CSIRO, welcomed the research and said the hypothesis – that stripes affected the flies’ vision – made sense.

“March flies and other biting flies have huge eyes and vision is important for finding animals to bite and suck their blood,” he said. “They are looking for big, dark, moving shapes. I know I’ve seen horse flies chasing slowly driving cars, for instance.

“The stripes break up the outline of the animal, which confuses the flies. This study took these findings in the clever direction of direct application to livestock animals. I think it makes sense and could be useful for farmers in the future.”

But Bayless said researchers needed to take the next step and address smell as well as sight. “Olfaction is also used by the biting flies to find hosts so painting stripes does not completely remove them,” he added.

“Direct comparisons of painted cattle with zebras in field experiments would be useful. The next step after field experiments is to understand better how the fly eye works with physiological data, what it really sees or not in terms of the stripes, in order to refine the colour pattern. A lot of refinement will be necessary before placing stripes on cattle can be widely viable.”