Category Archives: Orthoptera

Acoustic Defence in Bush Crickets: Sex Differences

bush crickets

Many insects produce sounds for mating, territory defence and to communicate with other conspecifics. However only insects in the order orthoptera stridulate their body parts (usually a leg and a wing) to produce sounds for defence. Insects usually protect themselves from predators using distastefulness, odours, colouration (cryptic and aposematic) or by startle and escape behaviour. Sound production has evolved in orthoptera in multiple species  (convergent evolution), and in many tettigoniid species the female has also evolved a ‘response song’.

In most tettigoniid only males have the sound-producing apparatus on their wings, which are rubbed together with a modified toothed vein on the left wing (the file) which is moved against the strong edge of the right wing (the plectrum). However both male and female bush crickets are capable of this defensive behaviour, although they evolved the stridulatory structures independently from one another. Scientists therefore wanted to discover whether there is a difference between the sexes, using the bush cricket (or katydid), Poecilimon ornatus, as a model.

It was found that females had a more varied syllable duration in their defence sound. The male sound last for significantly longer and contains more impulses, which is balanced by their increased tendency to regurgitate gut contents to repulse small predators such as ants and spiders.

It is thought that bush crickets rely on this method to defend themselves because their shorter wings (used for sound production) leave them unable to fly (escape) from predators. Another theory is that both male and female Poecilimon ornatus produce sounds to “evenly distribute” the increased predation risk among the sexes. The different exposure risk to the sexes may explain the differences in acoustic defence between the two sexes.

Kowalski, K. N., Lakes-Harlan, R., Lehmann, G. U., & Strauß, J. (2014). Acoustic defence in an insect: Characteristics of defensive stridulation and differences between the sexes in the tettigoniid< i> Poecilimon ornatus</i>(Schmidt1850). Zoology.

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