Behavioural responses of pine weevils to non-consumptive interactions with red wood ants

Non‐consumptive effects are increasingly recognized as important in predator–herbivore interactions, with both fundamental and practical implications. Notably, feeding damage to conifer seedlings by pine weevils, Hylobius abietis (L.), which are serious pests in forest regeneration areas, can be decreased by interactions with ants (Formicidae). To probe the behavioural mechanisms underlying such effects, which have rarely been described in predator–herbivore systems, we investigated how the ants influence the weevils' behaviour around planted conifer seedlings in the field. Half of the seedlings were infested with aphids and attended by red wood ants Formica polyctena Förster, whereas the others were used as controls. We asked whether the ants' behaviour towards the weevils differs between these treatments, and whether the weevils' movement behaviour (locomotion, stationary activity and digging) is affected by the treatments and physical interactions with ants. The ants attacked pine weevils more frequently and for longer periods around ant‐attended seedlings than around controls. Weevils' locomotion behaviour also increased markedly when attacked by ants. This may increase the likelihood of pine weevils moving away from, and causing less damage to, ant‐attended seedlings. This study demonstrates how non‐consumptive effects can be explained in terms of a herbivore's responses to a predator's aggressive behaviours. Non‐consumptive effects are increasingly recognised as important in predator–herbivore interactions. We investigated how red wood ants influence the behaviour of pine weevils around ant‐attended conifer seedlings infested with myrmecophilous aphids. The ants attacked pine weevils more frequently and for longer periods around ant‐attended seedlings than around control seedlings without aphids. Weevils' locomotion behaviour also increased markedly when attacked by ants. These results suggest that aggressive ant behaviour may be an important factor for behavioural change in pine weevils that approach ant‐attended seedlings which may explain the previously reported reduction in feeding damage on ant‐attended seedlings.