Desert Locust - Desert Locust Ecology

Desert Locust Ecology

The desert locust lives a solitary life until it rains. Rain causes vegetation growth and allows the female to lay eggs in the sandy soil. The new vegetation provides food for the newly hatched locusts and provides them with shelter as they develop into winged adults.

When vegetation is distributed in such a way that allow the nymphs, usually called hoppers, to congregate, and there has been sufficient rain for most eggs to hatch, the close physical contact causes the insects' hind legs to bump against one another. This stimulus triggers a cascade of metabolic and behavioral changes that cause the insects to transform from the solitary form to the gregarious form. When the hoppers become gregarious, they change from green-coloured to yellow and black, and the adults change from brown to red (immature) or yellow (mature). Their bodies become shorter, and they give off a pheromone that causes them to be attracted to each other, enhancing hopper band and subsequently swarm formation. Interestingly, the nymphal pheromone is different from the adult one. When exposed to the adult pheromone, hoppers become confused and disoriented, because they can apparently no longer "smell" each other, though the visual and tactile stimuli remain. After a few days, the hopper bands disintegrate and those that escape predation become solitary again. It is possible that this effect could aid locust control in the future.

During quiet periods, called recessions, desert locusts are confined to a 16-million-square-kilometer belt that extends from Mauritania through the Sahara Desert in northern Africa, across the Arabian Peninsula, and into northwest India. Under optimal ecological and climatic conditions, several successive generations can occur, causing swarms to form and invade countries on all sides of the recession area, as far north as Spain and Russia, as far south as Nigeria and Kenya, and as far east as India and southwest Asia. As many as 60 countries can be affected within an area of 32 million square kilometers, or approximately 20 percent of the Earth's land surface.

Locust swarms fly with the wind at roughly the speed of the wind. They can cover from 100 to 200 kilometers in a day, and will fly up to about 2,000 meters above sea level (thereafter, it becomes too cold). Therefore, swarms cannot cross tall mountain ranges such as the Atlas Mountains, the Hindu Kush or the Himalayas. They will not venture into the rain forests of Africa nor into central Europe. However, locust adults and swarms regularly cross the Red Sea between Africa and the Arabian Peninsula, and are even reported to have crossed the Atlantic Ocean from Africa to the Caribbean in ten days during the 1987-89 plague. A single swarm can cover up to 1200 square kilometers and can contain between 40 and 80 million locusts per square kilometer. The locust can live between three to six months, and there is a ten to 16-fold increase in locust numbers from one generation to the next.