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Locusts steer away from water by comparing how light is reflected off its surface to light reflected off land, say researchers.

They suggest that their findings, published last month (July 2005) in Biology Letters, could lead to new methods for keeping devastating swarms of locusts at bay, and protecting the crops they feed on.

Last year, Niger produced just 7.5 per cent of its usual production of its staple crop, millet. Locust swarms and drought led to a shortage of nearly 220,000 tonnes and to the famine that is devastating the country.

A team of scientists, led by Nadav Shashar at the Interuniversity Insitute of Eilat, Israel, were intrigued by the flight patterns of the desert locust Schistocerca gregaria during a swarm over the Sahara desert last November.

The locusts appeared to continually switch direction to avoid flying over water. When the wind blew them out over water, they immediately changed direction to return to land.

The team tethered 15 locusts to one-metre pieces of string. They found that the insects avoided flying over mirrors, which reflect light in a way similar to water. Instead, the insects preferred to keep to an area of ground with no mirror.

To translate this research into practice, the researchers say that using plastic sheeting to mimic the way the water reflects light could repel the locusts away from crop areas.

Locust swarms destroy crops in African countries every year, but last year the UN Food and Agricultural Organization (FAO) warned that swarms moving into Mauritania, Senegal and Mali were the worst in 15 years.

The insects went on to devastate vast regions of West Africa, where several governments were too poorly equipped to fight the attack.

Although locusts can cross large bodies of water, say the researchers, they avoid it because there is no food and shelter.

Usually, desert locusts live in the central Sahara, Arabia, and Persian
Gulf regions (green). When climate conditions are right, however,
as last year, they form swarms that migrate for thousands of
kilometres (yellow). Photo Credit: (NASA )

Reference: Biology Letters doi: 10.1098/rsbl.2005.0334 (2005)