Leaf vibrations produced by chewing provide a consistent acoustic target for plant recognition of herbivores

Plant defenses that respond to the threat of herbivory require accurate sensing of the presence of herbivores. Herbivory cues include mechanical damage, elicitors from insect saliva or eggs, and airborne volatiles emitted by wounded plants. Plants can also respond to the leaf vibrations produced by chewing herbivores. However, previous studies of the influence of feeding vibrations on plant defenses have been limited to single species pairs. In this study we test the hypothesis that chewing vibrations differ among herbivore species, both in their acoustic features and in their potential effect on plant defense responses. We first compare the acoustic traits of larval feeding vibrations in ten species from six families of Lepidoptera and one family of Hymenoptera. We then test responses of Arabidopsis thaliana plants to variation among feeding vibrations of different individuals of one species, and to feeding vibrations of two species, including a pierid butterfly and a noctuid moth. All feeding vibrations consisted of repetitive pulses of vibration associated with leaf tissue removal, although chewing rates varied between species and between large and small individuals within species. The frequency spectra of the vibrations generated by leaf feeding were similar across all ten species. Induced increases in anthocyanins in A. thaliana did not differ when plants were played vibrations from different individuals, or vibrations of two species of herbivores with different chewing rates, when amplitude was held constant. These results suggest that feeding vibrations provide a consistent set of cues for plant recognition of herbivores.