They will eat almost anything they come across, except each other. African migratory locusts (Locusta migratoria) can form large, crop-destroying pests while swarming. It is to be expected that during their migration they will occasionally eat a conspecific as a protein-rich snack – they also do this at lower densities. But due to the excretion of a specific pheromone, they show virtually no cannibalism in large pest swarms. write German and Chinese researchers in Science. This knowledge may be useful for future locust control.
Like the desert locust Schistocerca gregaria, which has been a major nuisance in recent years, the African migratory locust has a remarkable lifestyle: they generally live alone. They only seek out congeners to mate with. The eggs initially hatch into wingless offspring, called nymphs, which only develop into adult grasshoppers after five moults. Few nymphs survive in dry years, but after abundant rainfall the numbers can quickly increase and something strange happens: the solitary animals turn into group animals and can start swarming.
Swarm phase
With increasing group size, near-adult nymphs eat each other with some regularity, the researchers write. But the striking thing is that there is a limit to that cannibalism: if they are really close together, there is relatively little nibbling among themselves. This appears to be related to one of the seventeen volatile substances that migratory locusts excrete exclusively during the swarming phase: the pheromone phenylacetonitrile or benzyl cyanide. The disadvantage of this is that it seems to have an anti-aphrotic effect – which is perhaps also the reason that solitary migratory locusts do not yet produce the substance.
But the advantage is that the poisonous substance keeps enemies at a distance: its deterrent effect on birds had already been studied, and it now appears to work against hungry peers as well. The closer together the nymphs are, the higher the amount of phenylacetonitrile they excrete.
And experiments show that other nymphs prefer to stay as far away from the pheromone as possible – unless the receptor that allows them to perceive the substance has been switched off using the genetic technique crispr-cas.
Doomed
In a natural swarm, the amount of pheromone varies from individual to individual, the authors emphasize, so the nymphs with a low concentration of the substance still suffer. Nymphs that have been modified in such a way that they no longer excrete phenylacetonitrile are also doomed, according to the Science-article: they still end up in the stomach of a congener. According to the researchers, this offers prospects for combating locust plagues, although concrete solutions have not yet been found.