It is for good reason that locust swarm outbreaks are considered not only disastrous for the economy, but also for the livelihood of one in ten people in the world, according to some estimations. Locust swarms fly at speeds of around 20 km/h, and could contain billions of insects and spread across several square kilometers.
Desert locusts for example represent a major threat for parts of Africa, Middle East and Asia, as they are capable of consuming almost the equivalent of their body mass a day. Just last year, swarms six kilometers (3.7 miles) long have been reported in Australia.
However, these are normally solitary insects, living in areas where rainfall and vegetation are far from being abundant. But as the food becomes scarce (especially in desert areas), locusts start moving in large numbers toward regions with vegetation still in place. In addition to that, the rain favors not only an abundance in vegetation, but also favors breeding in large numbers of these insects.
According to experts, locusts start changing behavior while crowding, by seeking the company of other locusts, but they also start changing colors and developing larger muscles, the perfect asset for their long destructive flights.
In the early 1920s, these changes in colors misled scientists into believing they were dealing with different species of locusts.
But what causes them to form these swarms? Scientists reporting in the journal Science this week have isolated the biological reason behind this behavior, namely increased levels of chemical serotonin in the insects’ nervous system.
As Steve Rogers of the Cambridge University explained, the locusts gather into swarms driven by hunger and desperation. Experiments in the laboratory have shown that solitary locusts can be turned into gregarious ones by tickling their hind legs to simulate the crowd experience, scientists revealed.
Furthermore, the period coincides with a threefold but transient (less than 24 hours) increase in the amount of serotonin in the thoracic region of the nervous system.
In order to probe the effect of the serotonin, scientists inhibited its actions through specific chemicals and observed that the locusts were no longer becoming gregarious when the above mentioned stimuli were applied.
However, when injected with serotonin or chemicals that mimic serotonin, locusts turned gregarious even in the absence of other locusts, the researchers revealed. Furthermore, chemicals that increased the natural synthesis of serotonin enhanced gregarization when locusts were exposed to the tickling stimuli.
Serotonin is found in everything from plants, to humans and insects. Studies have shown that the chemical influences a number of activities in humans, such as emotional status, sexuality, appetite, body temperature and more. In addition to that, it is also used in the treatment of psychiatric disorders.
Dr. Swidbert Ott of the Cambridge University pointed out: Serotonin profoundly influences how we humans behave and interact, so to find that the same chemical in the brain is what causes a normally shy antisocial insect to gang up in huge groups is amazing.
The findings of the research work, which was supported by the Biotechnology and Biological Sciences Research Council, the Natural Sciences and Engineering Research Council of Canada and the Royal Society, appear today in Science.
