Days of the locust could be numbered

The mechanism that makes locusts swarm has been discovered at Oxford University, writes Andrew Morgan. A chemical foam produced by the insects causes them to form billion-strong plagues, which ravage Third World crops today as they did in Biblical times.

It has been discovered by Dr Stephen Simpson, at Oxford's Department of Zoology, and a colleague from the University of Reading, Dr Alan McCaffery.

They believe this chemical signal could be turned back on the locusts so they swarm prematurely, when no vegetation is available, and starve to death.

The findings are the most significant advance in years in combating the effects of these virulent grasshoppers which are capable of eating hundreds of thousands of tons of crops in a day. The United Nation's Food and Agriculture Organisation spends $350m a year trying to control locusts.

Desert locusts occur in two forms - solitary and gregarious. The solitary insects pose no problem if they stay in the desert but the threat occurs when they swarm and move on prevailing winds.

Dr Simpson caged a solitary locust and exposed it to others on the other side of a transparent screen, and to air which had passed over them. Neither the sight nor smell of other locusts had much effect. Then small paper pellets were used to simulate the presence of other locusts and buffet the caged insect. As a result of rubbing shoulders, the behaviour of the insect changed to that of the standard gregarious pattern.

Dr Simpson and Dr McCaffery found that females crowded for as little as four hours could lay eggs which turned out to be gregarious young. The researchers then discovered that removing the chemical foam in which these eggs were laid meant the gregarious young were born solitary instead.

Conversely, applying the foam to eggs which would have produced solitary young created gregarious insects instead. "Identifying this chemical is the next stage," said Dr Simpson.