The reactions of two species of aphid to chemotactile cues from a wolf spider match their vulnerability to predation

Abstract

AbstractVarious strategies have evolved to protect animals from predators. We explored the activity and predation risk experienced by two species of aphid. Both species will drop from plants when disturbed and face a suite of predators, including wolf spiders, when they reach the ground. We focused on Aphis fabae Scopoli and Aphis nerii Boyer de Fonscolombe (Hemiptera: Aphididae, Aphidini); A. nerii sequesters cardiac glycosides when it feeds on milkweed. We explored the interactions between these aphids and the wolf spider Pardosa milvina Hentz (Araneae: Lycosidae) that is likely a predator they encounter when they are not on their host plants. We hypothesized that there would be differences in the susceptibility of the two species to predation and that the more vulnerable species would react more strongly to substrate‐borne cues deposited by the spider. We predicted that any behavioral reactions that the aphid displayed in response to predator cues would be effective in reducing risk. We documented the activity of each aphid species on chemotactile cues from P. milvina and measured predation rate in arenas with and without those same cues. Aphis fabae altered their activity in the presence of P. milvina cues but A. nerii did not. Likewise, A. fabae was more susceptible to predation by P. milvina when no cues were present, but when cues were present, predatory success was much lower. Aphis nerii, the less desirable prey for this predator, moved less and had a different locomotory pattern than A. fabae in control trials with no spider cues and so we cannot determine whether its chemical protection or activity were more important in reducing predation levels. These results provide insight into the risks faced by aphids when they are off of their host plant and in a barren environment.