Volatiles released by damaged leaves of Piper mollicomum (Piperaceae) act as cues for predaceous wasps: evidence using plasticine dummies as herbivore model

Abstract

Volatiles released by damaged plants are used as cues by predators and parasitoids to find their herbivorous prey. Here, we assessed whether odor cues released by simulated herbivore-damaged leaves in Piper mollicomum attract predaceous wasps. We applied plasticine dummy caterpillars as an herbivore model to evaluate predation risk on undamaged and artificially damaged leaves by the mandible marks left by foraging wasps. Despite observing a tendency of a visual component in the wasp attraction (more marks on dummies under old naturally damaged leaves), we observed that chemical cues play a crucial role, with recent artificial damage and leaves baited with volatile essential oils of P. mollicomum attracting more wasps for the dummies than those untreated. Headspace analysis by GC–MS showed that undamaged leaves released small amounts of compounds, while damaged ones released 63 times more volatiles, which consisted of a blend containing mostly mono- and sesquiterpenoids. Histochemical tests revealed that terpenoids are located in oil cells spread among the leaf tissue, and may be released by the disruption of such cells when herbivores are feeding on leaves. We suggest that signals of disrupted plants differ from the mosaic of odor blends emitted by the background environment and may provide a detectable, although not necessarily specific, cue for prey presence. Such detectable cues are important for generalist foraging predaceous wasps, since they spend time searching for prey in different host plants.