Aphids detect approaching predators using plant-borne vibrations and visual cues

Aphids (Hemiptera: Aphididae) have a repertoire of defensive behaviors against insect predators and parasitoids that includes kicking, twitching, walking away and dropping off the plant. These defensive responses, which are most effective when aphids receive early warning of an approaching predator, are often initiated before the predator reaches the aphid. Although described before, the process of predator detection has practically never been experimentally investigated in aphids and it is currently unknown whether they can distinguish approaching predators from harmless insects, and which senses they use for pre-encounter predator detection. I therefore addressed these two questions by comparing seven behavioral responses of pea aphids (Acyrthosiphon pisum) to approaching predators (ladybugs) and non-predators (variegated caper bugs), to the plant-borne vibrations they generate and to visual cues. Aphids kicked, raised their bodies, withdrew their stylets and dropped more often in response to approaching ladybugs. Visual cues elicited only antennal movements. Body raising and antennal movements were more frequent in response to ladybug vibrations compared to caper bug vibrations. I found no evidence for predator-odor detection. Stylet withdrawal (preparation for escape) and dropping occurred in response to climbing insects but not to vibrations. I conclude that pea aphids use multimodal cues to detect approaching coccinellid predators. While visual cues alert the aphid without triggering defensive responses, vibrational cues are used to distinguish predators from non-predators. Future research on vibration patterns that aphids interpret as signs of danger may lead to the development of novel management techniques for one of the world’s worst crop pests.