1.00pm - By STEVE CONNOR
There is nothing new to the idea of a locust plague. The desert locust is depicted in the bas-reliefs carved into the ancient tombs at Saggara in Egypt and it was the insect described in the Book of Exodus as the cause of the eighth
plague that dogged the Pharoah.
One of the unusual features of the desert locust is that it can exist in two seemingly different forms. One is solitary and almost harmless and the other is gregarious, with a voracious appetite for any greenery that it encounters.
In fact, so different were these two forms of Schistocerca gregaria that scientists did not even think them to be the same species until the 1920s. Precisely why and how the solitary form can transmute into the gregarious form is still a matter of some dispute among many entomologists.
The answer appears to lie in the lifecycle of the insect. Female adults lay up to 200 eggs at a time in holes they dig out of wet ground. Thousands of locust eggs can be buried in a square-metre patch of land.
After hatching, the young "hopper" locust passes through five or six stages of growth before it finally emerges as a fully mature adult with wings. It is during the growing hopper stages that the locust eats most voraciously.
One of the neat tricks the locusts can perform is to alter the speed at which they develop to suit the availability of food or wet weather. When conditions are poor, they slow their metabolism. When conditions get better, the life cycle speeds and they mature faster.
When hoppers find themselves living in densely populated conditions, they undergo a change in behaviour and colour to become the gregarious, swarming form of the species. Solitary hoppers, born green can under these conditions turn into the mature, yellow form and go on to swarm.
There is no evidence that locust plagues occur with any regularity. There were five occasions in the 20th century when deserts locusts swarmed but for no obvious reason other than because the wet weather and food supply were favourable.
The present plague is almost certainly going to get worse before it gets better.
More breeding will take place this month and even larger swarms could begin to appear by mid-September to threaten the autumn harvest. At present, the only effective method of locust control is by spraying with organophosphate chemicals applied in what the FAO describes as "small, concentrated doses" from sprayers mounted either on vehicles or light aircraft.
For farmers living in the affected areas, the environmental price of using such pesticides seems a small one to pay.
As 82-year-old Amadou Binta Thiam, in the affected region of Mauritania, said: "I have a big family. Twenty people depend on me. We have no children working outside who can send me money. If locusts get my field, it is a real catastrophe."
Similar sentiments were expressed by Ahmed Ould Bah, a local herdsman who relies on good pasture land.
"When the locusts spend the night here, they don't leave anything. I have to go farther and farther away to find grazing."
Locusts may seem an ancient plague from a distant time, but they are still capable of causing a very modern misery.
- INDEPENDENT
1.00pm - By STEVE CONNOR
There is nothing new to the idea of a locust plague. The desert locust is depicted in the bas-reliefs carved into the ancient tombs at Saggara in Egypt and it was the insect described in the Book of Exodus as the cause of the eighth
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