Tricking locusts into staying at home
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CTA. 1996. Tricking locusts into staying at home. Spore 61. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/47247
Scientists at the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya have decoded the locust's chemical language, and they can now stop them swarming. Kept in their home territories, the locusts become more vulnerable to attack...
Scientists at the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya have decoded the locust's chemical language, and they can now stop them swarming. Kept in their home territories, the locusts become more vulnerable to attack by birds and more susceptible to insecticides and diseases. Locusts, and their near relatives grasshoppers, usually live solitary lives, but from time to time they change their behaviour to form large swarms: hoppers (the growth stage between hatching and adult) will come together or aggregate, the adults becoming gregarious. These swarms migrate to new areas, doing immense damage as they progress across the countryside. The ICIPE scientists have, for several years, been looking for ways to stop locusts from swarming. They argued that control would be easier if aggregation could be prevented or reversed, reversed, confining the pests to their home areas. So they have been studying the chemical messages that trigger changes in the locust's behaviour. The scientists have found that desert locusts have a large repertoire of chemical smells or pheromones. At each growth stage, hoppers and adults have their own blend of pheromones. Older gregarious adults use an enriched version of the pheromone blend that young adults use for aggregation; the hopper stages have radically different pheromones from those of adults and, again, the first stage or first instar hoppers have a different signal from that of other hoppers. Moreover, the researchers have observed that if an inappropriate or unfamiliar pheromone is given to an adult or a hopper, it has drastic effects. For instance, when the aggregation pheromone produced by the gregarious adult is sprayed on gregarious hoppers it drives them crazy setting one against the other. When this pheromone was tested in the field on gregarious hoppers, it stopped them coming together prior to swarming. They then reversed their behaviour, broke up into small groups, and eventually dispersed. That was the change of behaviour the scientists were looking for, but they got an unexpected bonus. The pheromone, for some reason still unknown, weakens the insect's immune system, and they become very susceptible to low doses of insecticides and very prone to infection from pathogens. Using the pheromone stops swarming and then offers an opportunity to apply low doses of insecticide or biological spray to get an effective kill. There is also greater predation by birds. Large swarms tend to frighten birds away, but when locusts are dispersed, the birds pick them off easily. The effect of the pheromone is to give a good kill, at far less damage to the environment and at minimal cost. If the pheromone is to work effectively there will have to be good monitoring of the known breeding grounds and as soon as aggregation is noticed, the pheromone can be applied, followed by spraying with insecticides or pathogens. Further trials are needed and it is hoped the pheromone will be available in three years. Tests on other locust species and grasshoppers will also be carried out. ICIPE P O Box 30772 Nairobi KENYA