Field evidence for the role of plant volatiles induced by caterpillar-derived elicitors in the prey location behavior of predatory social wasps

1. One assumed function of herbivore-induced plant volatiles (HIPVs) is to attract natural enemies of the inducing herbivores. Field evidence for this is scarce and often indirect. Also, the assumption that elicitors in insect oral secretions that trigger the volatile emissions are essential for attraction of natural enemies has not yet been demonstrated under field conditions.
2. After observing social wasps removing caterpillars from maize plants in an agricultural field, we hypothesized that these wasps use HIPVs to locate their prey. To test this, we conducted an experiment that simultaneously explored the importance of caterpillar oral secretions in the interaction.
3. We found that Spodoptera caterpillars placed on mechanically damaged plants treated with oral secretion were more likely to be attacked by wasps compared to caterpillars on plants that were only mechanically wounded. Both of the the latter treatments were considerably more attractive than plants that were only treated with oral secretion or left untreated. Subsequent analyses of headspace volatiles confirmed differences in emitted volatiles that likely account for the differential predation events across the treatments.
4. These findings highlight the importance of HIPVs in prey location by social wasps and provide evidence for the role that elicitors play in inducing attractive odor blends.