UK: Serotonin causes locusts' personality change

It just takes a little tickling to turn the usually solitary locust into the swarming monster that devastates crops around the globe. But more importantly, researchers have now found the chemical responsible for the change - serotonin.

Scientists in the UK and Australia tickled the legs of locusts to simulate the jostling that occurs when food shortages force large numbers of locusts together. After just two hours, the locusts displayed a threefold but short-lived increase in the amount of serotonin in their bodies. At the same time, the locusts changed colour, developed more muscle and actively sought one another's company.

The research, reported in Science, included tests to check that the serotonin was indeed responsible for the change. Dr Michael Anstey, an author of the paper from the University of Oxford, said:

"Up until now, while we knew the stimuli that cause locusts' amazing 'Jekyll and Hyde'-style transformation, nobody had been able to identify the changes in the nervous system that turn antisocial locusts into monstrous swarms. The question of how locusts transform their behaviour in this way has puzzled scientists for almost 90 years, now we finally have the evidence to provide an answer."

Another of the researchers, Dr Swidbert Ott, from Cambridge University, said serotonin profoundly influenced how humans behave and interact, and it was amazing to find that the same chemical caused a normally shy antisocial insect to gang up in huge groups.

The research was funded by the Biotechnology and Biological Sciences Research Council, the Natural Sciences and Engineering Research Council of Canada and the Royal Society.

To check that serotonin was behind the change, the locusts were injected with chemicals that blocked the action of serotonin on its receptors: when these locusts were exposed to the same gregarising stimuli, they did not become gregarious.

Chemicals that blocked the production of serotonin had the same effect. The scientists also found that locusts injected with serotonin or chemicals that mimic serotonin, turned gregarious even in the absence of other locusts. Finally, chemicals that increased the natural synthesis of serotonin enhanced gregarisation when locusts were exposed to the tickling stimuli.