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They know better than most humans how to regulate their food intake to ensure that they eat a balanced diet. As swarms of desert locusts move around, they are held together largely by what smells to humans like sour beer. This strong odour is produced by bacteria living in the locust's gut. These and other strange facts about desert locusts have recently been discovered by scientists working in the universities of Bath, Southampton and Oxford in the United Kingdom. This research is helping to identify targets for badly needed new locust control measures. It is also telling scientists more about the nervous systems of insects in general, and about the complex and mutually beneficial relationships which can evolve between animals of many kinds, as well as humans, and bacteria living in their guts. Swarms of desert locusts periodically devastate crops in 60 countries around the tropical world. They are capable of consuming their own body weight (two grams) of food each day. The larger swarms are composed of billions of locusts, covering several hundred square kilometres and travelling up to 130 kilometres per day. "For 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 of the University of Southampton, whose research group is investigating how desert locusts literally taste their environment. Locusts' sense organs are quite unlike our own and they experience the world in a very different way from us. They smell and taste the world around them through microscopic hair which covers their legs as well as their mouthparts and are sensitive to touch as well as chemicals. Chemicals enter the hair through holes on their ends and stimulate sensory taste cells inside each hair. Southampton University researchers led by Dr Philip Newland have given locusts several kinds of foodstuffs such as salts, proteins and carbohydrates to taste with their hairy legs. Dr Newland and his colleagues measured the response of the locusts to different concentrations of these chemicals, by seeing what concentrations of chemicals were required to make locusts move away, and by studying the electrical response of the brain to them. Meanwhile scientists at Oxford University have been studying how desert locusts achieve a balanced diet, by feeding them different assortments of foodstuffs in varied proportions. Amazingly, they found that locusts will eat precisely five times as much food as normal when fed food diluted five fold with indigestible cellulose with no nutritive value. Locusts, the Oxford team found, also select their food intake to compensate for any past dietary deficiencies and to give themselves the right balance of proteins, carbohydrates and salts. Even locust faeces has its uses for the swarm. Researchers at the University of Bath in western England have found that two smelly vapours given off from locust faeces, guaiacol and phenol, which to humans smell like stale beer, act as attractant pheromones (hormones which act outside the body) and help to keep the swarm tightly packed together. Painstaking research has shown that these volatile compounds are in fact produced not by the locust itself but by bacteria living in its gut. High concentrations of these pheromones indicate to other locusts that good environmental conditions exist for plant growth and egg laying. This research is of great theoretical interest to scientists studying nervous and sensory systems, and others studying symbiotic relationships between gut bacteria and their hosts. But it also has future implications for locust control. Ways may be found to damage the locust's nervous system with selective chemistry, or to block its aggregatory pheromones or to use them to mislead a swarm and direct it away from crops or into traps. Or locusts might be misled into accepting poisons as food. These are only a few possibilities among many others. What is certain is that we need to find more weak points in a pest that in recent times has devastated large areas of Mali, Mauritania, Kazakhstan, Uzbekistan, Russia, China and several other countries. Source: London Press Service, web site at:
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Despite their ability to ravage crops in swarms, desert locusts spend most of their five-month lifetime as shy, solitary individuals who are incredibly fussy eaters.
