Oral Secretions Affect HIPVs Induced by Generalist (Mythimna loreyi) and Specialist (Parnara guttata) Herbivores in Rice

Plants synthesize variable mixtures of herbivore-induced plant volatiles (HIPVs) as part of their evolutionary conserved defense. To elucidate the impact of chewing herbivores with different level of adaptation on HIPV profiles in rice, we measured HIPVs released from rice seedlings challenged by either the generalist herbivore Mythimna loreyi (MYL) or the specialist Parnara guttata (PAG). Both herbivores markedly elicited the emission of HIPVs, mainly on the second and third days after attack compared to control plants. In addition, side-by-side HIPV comparisons using MYL and PAG caterpillars revealed that generalist feeding induced comparably more HIPVs relative to specialist, particularly on day two as highlighted by multivariate analysis (PLS-DA) of emitted HIPVs, and further confirmed in mimicked herbivory experiments. Here, mechanically wounded plants treated with water (WW) released more VOCs than untreated controls, and on top of this, oral secretions (OS) from both herbivores showed differential effects on volatile emissions from the wounded plants. Similar to actual herbivory, MYL OS promoted higher amounts of HIPVs relative to PAG OS, thus supporting disparate induction of rice indirect defenses in response to generalist and specialist herbivores, which could be due to the differential composition of their OS. (196 words).