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 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.
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"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.
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