Abdominal sensing of substrate vibrations in insects

Mechanosensation is a universal sensory modality and respective receptors in insects are located in all body parts. For perception of substrate vibrations, highly specialized sensory organs have evolved. In insects, the legs contain specialized vibration sensors, but insects also touch the substrate with other body parts, like their abdomen. Here, we used extracellular recordings from abdominal nerves to test for vibrational sensitivity in two evolutionarily distant insect species. Vibrational stimuli of defined frequencies (30 Hz - 10 kHz) and accelerations (0.01 - 10 m/s²) were applied to the caudal region of the abdomen while recording from nerves associated with mechanosensitive chordotonal organs. In the grasshopper Schistocerca gregaria (Forsskal), abdominal nerves are almost as sensitive to substrate vibrations as the leg nerves. In the cicada Okanagana rimosa (Say), the sensitivity of abdominal sense organs is even higher than that of the leg associated sense organs. In both species, their abdominal tympanate ears are also sensitive to substrate vibrations. The results show that chordotonal organs in the abdomen can significantly contribute to vibration perception in insects.