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

Abstract

Summary Plants produce herbivore‐induced plant volatiles ( HIPV s) in response to damage by herbivores. Although HIPV s are known to enhance plant resistance by affecting herbivore host plant preferences and by attracting natural enemies, little is known about the role of HIPV s on the resistance of neighbouring plants and the mechanism behind this associational resistance. This study examined the effect of HIPV s from herbivore‐damaged host plants (alfalfa ( M edicago sativa ), clover ( T rifolium alexandrinum ) and cotton ( G ossypium hirsutum )) on oviposition by E gyptian cotton leafworm ( S podoptera littoralis ) ( L epidoptera: N octuidae) on neighbouring, undamaged host plants. There was a significant reduction in oviposition by S . littoralis on undamaged plants adjacent to herbivore‐damaged cotton plants under both field and laboratory conditions. The results showed that the associational resistance by HIPV s depends on direct effects on oviposition behaviour in S . littoralis . There were also indications that other mechanisms may be involved. Associational resistance via HIPV s was not observed for all plant species tested. Emission of HIPV s from damaged cotton increased the resistance of undamaged cotton and alfalfa plants to oviposition by S . littoralis , but HIPV s from damaged alfalfa and clover neighbours did not provide resistance to undamaged cotton plants. Synthesis . Our results suggest that the presence of HIPV ‐emitting plant neighbours can reduce herbivory on undamaged plants and enhance plant resistance by affecting oviposition behaviour in insect herbivores.