Locust nymph eating lettuce

The swarming response results in a number of changes in the locust: alteration of the normal camouflage to more striking colouration and the change in behaviour that causes them to gather together into a swarm (called a band if they are nymphs).

Scientists knew about the physical stimuli which causes swarming but were uncertain about the underlying biochemical changes. The physical stimulus was experimentally demonstrated using a small paintbrush to ‘tickle’ the locusts and found that the hind femora was the most effective site for inducing swarming (Simpson et al, 2001).

The hind femora caused the highest percentage, 76% to 100% (shown in red), of S. gregaria to exhibit swarming behaviour (adapted from Simpson et al, 2001). © Malin Nikunlassi

Recently scientists discovered the major component of the signalling pathway which results in swarming: the neurochemical serotonin (Anstey et al, 2009), a neurotransmitter found in many organisms, from insects to humans.

Serotonin - based on the amino acid tryptophan with an additional hydroxyl group (OH) marked in red. © Malin Nikunlassi

Knowledge about the role that serotonin plays may provide new novel ways of controlling the locusts without resorting to mass spraying of pesticides.

For additional reading on locusts and grasshoppers as pest species, visit the International Society for Pest Information which has a number of freely available full text resources.

References:

Simpson S.J., Despland E., Hägele B.F. and Dodgson T. (2001) Gregarious behavior in desert locusts is evoked by touching their back legs. PNAS 98: 3895-3897

Anstey M.L., Rogers S.M., Ott S.R., Burrows M. and Simpson S.J. (2009) Serotonin Mediates Gregarization Underlying Swarm Formation in Desert Locusts. Science 323: 627-630