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Plague of locusts invade central London

June 28, 2001

Locusts are incredibly fussy eaters, use beer-smelling perfume to attract their friends and do exactly what their mothers tell them, according to scientists exhibiting at the Royal Society's Summer Science Exhibition from 3-5th July in London next week. Researchers from Bath, Oxford and Southampton Universities will showcase their latest findings on the voracious insects currently wreaking havoc through parts of Central Asia. The One of the Crowd display will feature a small "swarm" of the desert locust - Shistocerca gregaria.

Locusts are notorious, swarming pests capable of consuming their own body weight [2 grams] of food each day. Swarms can be made up of billions of locusts, covering several hundred square kilometres and travelling distances of up to 130 km per day. "For these swarming locusts, the sense of taste plays a vital role in affecting decisions about feeding, the selection of egg-laying sites and the avoidance of noxious chemicals," says Dr Philip Newland from the University of Southampton whose research group are investigating how locusts 'taste' their environment.

Rather than taste buds - the locust has tiny 'hair-like' sensors all over its body. When one of these is triggered, a burst of nerve impulses flashes through the locust's nervous system. By measuring these impulses, and the locust's reaction, the team can understand how locusts accept or reject food, and select appropriate egg-laying sites. At the University of Oxford, researchers have found that locusts use this neural data about their food to make sure they are eating a balanced diet. When their food is diluted 5-fold with indigestible cellulose material, the locust will eat five times as much food to make sure it reaches optimal 'intake targets' for protein, carbohydrate and salt.

At Oxford, Professor Steve Simpson and colleagues are also investigating how locusts switch their behaviour and appearance between swarming and non-swarming varieties. Overcrowding caused by food scarcity forces locusts to converge on food sources, where their vast numbers mean that their hind-leg sensors are rubbed against each other, causing them to switch to the swarming phase. They also found that female locusts pass on messages to their offspring before they are born - telling them whether to be swarming or non-swarming when they hatch out. The female gets her knowledge from her own experience and also picks up information from her mate as they go through courtship and mating rituals.

Once a swarm forms, high concentrations of perfume smelling of gone-off beer help keep the swarm together. The research group from Bath has shown that tiny bacteria living inside the guts of locusts break down food to make some of the key components of these "cohesion pheromones". These beer-smelling pheromones are produced by the bacteria in the gut, and are then excreted in the locust's faeces. A high concentration of these odours in wet faeces signals to other locusts that the best environmental conditions for plant growth and egg development are present. One area of fascination for scientists is how the bacteria and the locust evolved such a unique relationship.



Biotechnology and Biological Sciences Research Council (BBSRC)