Oviposition-induced plant volatiles prime defences against impending herbivores in neighbouring non-damaged plants.

Plants exploit environmental cues about the risks of encountering insect herbivores, often sensitising defensive responses. While herbivore-induced plant volatiles (HIPVs) are reported to enhance plant defences against incoming herbivores, responses to oviposition-induced plant volatiles (OIPVs) are massively under-explored. We studied whether OIPV emissions from Brassica napus enhance defences in non-damaged neighbouring B. napus when subsequently infested with Pieris brassicae larvae. We collected and analysed the emission rates of plant volatile organic compounds under different treatments and measured P. brassicae larvae biomass as a proxy for defence. We show that oviposition triggers the release of specific volatiles, i.e. α-pinene, dimethyl-trisulfide, and limonene, potentially serving as herbivore early warning cues for neighbouring non-damaged plants. Initially, after three days of herbivory, OIPV-receivers emitted lower levels of volatiles compared to control receivers; however, following seven days of herbivory, both control and OIPV-receivers emitted similar amounts of volatiles. We suggest a potential trade-off between direct and indirect defences, with sensitised plants investing metabolic resources initially towards direct and later enhancing indirect defences. We show that OIPVs mediate plant-plant communication, a natural potential for Brassicaceae crop protection.