BioEd Online

Locusts, what locusts?

The insect in question is the desert locust, Schistocerca gregaria (Forskal), a type of grasshopper that usually lives in the deserts of Africa and Asia. The insects emerge from eggs laid in sandy soil, develop into wingless 'hoppers' on the ground and then mature into winged locusts.

And what do they do?

When the insects are sparse, they act autonomously. But when they build up a critical mass, they change colour and start acting together, forming moving carpets of 'hoppers' and then winged swarms that can span several hundred square kilometres. A swarm can consume the same amount of food in one day as several thousand people. Widespread swarms, called plagues, occur sporadically and have been reported since ancient Egyptian times.

Where did they come from and where are they heading?

Two days of torrential rains in western Africa last October encouraged the insects to breed and lay their eggs in wet sand. They later moved northwards to Morocco, Algeria, Tunisia and Libya. This year, favourable weather conditions have vastly increased their numbers. Despite efforts to control them, the first swarms are forming and heading back to northwestern countries, including Mauritania, Senegal and Mali. The locusts are soon expected to spread east towards Niger, Chad and Sudan.

Update 29 July 2004 At the end of July, the FAO warned that the situation is worsening. The number of swarms invading Mauritania, Senegal and Mali has increased, although control measures are having some effect in Northwest Africa. Rains are expected to encourage breeding and boost numbers further. Nine countries met in Algiers on 27 July to start drawing up an action plan on how best to tackle the swarms.

How serious is the threat?

Extremely serious, according to experts. So far, the scale of the infestation is on a par with the growth of the last plague in 1987-89, which affected 28 countries. The worst-case scenario is that they will strip subsistence crops in areas that are already suffering severe food shortages because of civil war or drought. "It's the most serious situation we have had in the past fifteen years," says Keith Cressman of the FAO, who forecasts locust infestations.

How can the creatures be controlled?

Locusts are mainly curbed using chemical pesticides, such as the organophosphate malathion, which is sprayed from vehicles and aeroplanes. Unfortunately, this kills insects and the toxin can accumulate in birds, lizards and other animals that feed on the poisoned insects.

An alternative, but still experimental, way to combat the desert locusts is with spores of a Metarhizium fungus that infects and kills the insects. It has been tested against a related species of locust in areas of Australia where there are endangered birds, livestock or organic crops. But there are downsides: the fungus costs more than conventional pesticides; takes a week or two longer to kill; and the infrastructure is not present to produce large enough quantities to fight the swarms that may shortly descend.

Will it be difficult to stamp them out?

Yes. One of the hardest things is tracking down the bands of hoppers, which cover just a few square metres, in several hundred square kilometres of desert. This requires countless aeroplanes and cars. Research into alternative methods has dried up, because interest has died since the last plague.

Another problem is that vital information may not be shared, because some of the northern African countries are reluctant to admit holes in their control policies. "It's hard for a country to admit a swarm has left the country and that they weren't effective," says entomologist and locust expert Arnold van Huis of Wageningen University in the Netherlands.

Is there enough cash?

No. The 1987-89 plague cost more than US$300 million to quell, and this time experts say there are critical shortfalls in the stock of pesticides available and in money to buy more. The FAO says it needs an extra $10 million to $20 million for this summer and autumn and is calling on donor agencies to cough up more money, but it has to compete with other humanitarian demands. "If people are not dying it's not an emergency," says van Huis.

What will happen next?

Whether the early swarms develop into vast ones partly depends on the weather: rains will escalate the problem and dry weather could assuage it. But some say that a plague is almost unavoidable without drastic intervention. We will see much bigger swarms in the coming weeks, predicts Cressman.