Herbivore-induced plant volatiles prime two indirect defences in lima bean

Abstract

Herbivore-induced plant volatiles (HIPV) are emitted by plants in response to herbivory and attract natural enemies of herbivores, thereby inducing an important indirect defence against herbivores. Evidence supports the hypothesis that plants become more defensive against herbivores after exposure to HIPV and that this is a type of priming, or preparation by the plant perceiving an HIPV signal to respond to herbivory. We report the priming of two induced indirect defences: HIPV-mediated induction of predator attraction and the secretion of extrafloral nectar (EFN), known as an alternative food source for natural enemies of herbivores. When uninfested lima bean plants (Phaseolus lunatus) were exposed to HIPV, the plants attracted more predatory mites (Phytoseiulus persimilis) and secreted larger amounts of EFN than unexposed plants. Further, when HIPV-exposed plants were infested by spider mites (Tetranychus urticae) for 2 days, the plants attracted more predators and secreted larger amounts of EFN than plants that were infested for 2 days after exposure to uninfested plant volatiles. However, there were no differences in the attraction and the EFN secretion when they were infested for 4 days. Predatory mites survived longer when supplied with EFN and stayed longer on uninfested plants that had been supplemented with additional extrafloral nectar. From these results, we conclude that the priming of HIPV-exposed plants recruits predators and induces the secretion of EFN that functions to protect the plants before and after herbivory.