Ladybird footprints induce aphid avoidance behavior

Predation has immediate consequences for prey fitness and early assessment of predation risk may be advantageous for prey. We investigated the ability of the bird cherry-oat aphid, Rhopalosiphum padi (L.), to detect one of its important predators, seven spot ladybird, Coccinella septempunctata L., via chemicals in the predator's walking track. Ladybird tracks left on leaves elicited avoidance and reduced host plant settling in aphids via contact and olfactory cues or a combination of both. Aphid avoidance behavior was dependent on ladybird sex and number of individuals, with the odor of a single ladybird eliciting attraction and the odor of several ladybirds causing avoidance. This suggests that aphids may be able to assess the risk of predation via the extent of the chemical tracks and adjust their behavioral response accordingly. Aphid responses to ladybird tracks decreased with the age of the track, potentially preventing aphids from avoiding plants on which predators have not been recently active. This avoidance mechanism may play an important role in the biological control exerted by predatory ladybirds on aphid populations. (C) 2012 Elsevier Inc. All rights reserved.