Multifunctional aspects of leaf beetles-induced willow leaf volatiles

Several herbivorous and carnivorous arthropods are known to exploit herbivore-induced plant volatiles (HIPVs) in different ways. We have been interested in such multifunctional aspects of HIPVs. Here we focused on a tritrophic system of willow plants (Salix eriocarpa), specialist herbivorous leaf beetles (Plagiodera versicolora) and predatory ladybird beetles (Aiolocaria hexaspilota). The predatory beetles prey only on the larvae of the leaf beetles. In a Y-tube olfactometer, we showed that volatiles from leaves infested by the leaf beetle larvae attracted the predatory beetle adults over those from intact leaves, suggesting that HIPVs were exploited by the predators as information indicating the presence of prey. By contrast, volatiles from leaves infested by adult beetles did not attract the predatory beetles over intact leaf volatiles. Interestingly, the adult-induced volatiles attracted the conspecific leaf beetle adults over the intact leaf volatiles, indicating that the volatiles functioned as information on the presence of available food resources. Chemical analysis showed the qualitative and quantitative differences between beetle larvae induced leaf volatiles and beetle adults-leaf volatiles. In this system, our results suggested that differentiation of quantity and quality of HIPVs was adaptive traits for the plant, which avoided the attraction of herbivores but enhanced the attraction of predators.