Herbivore‐induced plant volatiles provide associational resistance against an ovipositing herbivore

Summary Plants produce herbivore‐induced plant volatiles (HIPVs) in response to damage by herbivores. AlthoughHIPVs are known to enhance plant resistance by affecting herbivore host plant preferences and by attracting natural enemies, little is known about the role ofHIPVs on the resistance of neighbouring plants and the mechanism behind this associational resistance. This study examined the effect ofHIPVs from herbivore‐damaged host plants (alfalfa (Medicago sativa), clover (Trifolium alexandrinum) and cotton (Gossypium hirsutum)) on oviposition byEgyptian cotton leafworm (Spodoptera littoralis) (Lepidoptera:Noctuidae) on neighbouring, undamaged host plants. There was a significant reduction in oviposition byS. littoralison undamaged plants adjacent to herbivore‐damaged cotton plants under both field and laboratory conditions. The results showed that the associational resistance byHIPVs depends on direct effects on oviposition behaviour inS. littoralis. There were also indications that other mechanisms may be involved. Associational resistance viaHIPVs was not observed for all plant species tested. Emission ofHIPVs from damaged cotton increased the resistance of undamaged cotton and alfalfa plants to oviposition byS. littoralis, butHIPVs from damaged alfalfa and clover neighbours did not provide resistance to undamaged cotton plants. Synthesis. Our results suggest that the presence ofHIPV‐emitting plant neighbours can reduce herbivory on undamaged plants and enhance plant resistance by affecting oviposition behaviour in insect herbivores.