Maths link to future locust dispersal

(Reuters) - A mathematical model of locust swarms could help in the development of new strategies to control their devastating migration, according to British researchers.

Mathematicians at the universities of Bath, Warwick, and Manchester analyzed the movements of different group sizes of locusts that had been filmed by colleagues at the University of Adelaide. By studying the interactions between individual locusts they were able to create a mathematical model mimicking the pest’s collective behavior.

Locust plagues can cause havoc when they occur in Africa, the Middle East, Asia, and Australia. Flocks can quickly procreate until they are in the tens of millions, with each individual eating its weight in food every day, namely pastureland that livestock and other animals graze on.

In March 2013 in Madagascar, around half of the country was infested by swarms of locusts.

The new research shows for the first time that locusts interact with several of their immediate neighbors when deciding the direction in which they march. The more locusts join the swarm, the less directional switching occurs, resulting in a more stable swarm.

According to co-author Dr Christian Yates, of the University of Bath, “they (the Adelaide researchers) took a ring-shaped arena.....there was an area in the middle where the locusts couldn’t go and they put a wall round the outside. They put a few locusts into the arena, and they watched to see what these locusts would do.”

He added: “When you put five or six locusts into the arena like we have here they just march around randomly, they don’t really pay much attention to each other. But as soon as you put more locusts into the arena they all start to march together around the arena in the same direction, so either clockwise or anti-clockwise, and occasionally spontaneously, these locusts will all switch direction all at the same time and start to move in the other direction around the arena.”

While swarming, locusts usually move in the same direction as their immediate neighbors, but then spontaneously switch direction together as a group. This behavior is replicated in other animal groups such as starlings and fish.

Researchers also made a crucial finding regarding the ability of locusts to forcibly change the behavior of others in the flock.

“The most important thing we found in our research was that if you take two locusts coming in one direction and one in the other then these two locusts can turn this individual, and if you don’t include this ‘two meets one’ interaction then you find that you can’t replicate these startling switches of behavior that you see in the locusts, the same sorts of things that you might see in flocks of starlings changing direction quickly or in schools of fish,” said Yates.

By creating a model that mimics the collective behavior of the insects Yates believes it will be possible to develop new strategies of disrupting swarms. Yates says the team’s discovery that locusts are sensitive to randomness, making the swarm less stable, could be useful.

“If we can somehow increase the external noise that these locusts are experiencing then we might be able to break up the swarm, isolate the individuals, and deprive them of the benefits of being in a swarm,” said Yates.

He added: “These locusts can fly, as well as just marching, so one option is to maybe fly planes close to the locusts which will increase the disturbances in the air. Other possibilities are maybe using some sort of ultrasonic device to disturb the locusts.”

The study, co-authored by Dr Louise Dyson, of the University of Warwick, Professor Alan Mckane from the University of Manchester and Dr Jerome Buhl from the University of Adelaide, was published in the journal Physical Review E.

Previous research by the same team revealed that locusts align themselves with their neighbors so their vulnerable flanks are not exposed to cannibalistic attack.