From hindrance to indirect protection: Ant‐mediated enemy‐free space for gall midges ( <scp>C</scp> ecidomyiidae) on <i>Macaranga</i> myrmecophytes ( <scp>E</scp> uphorbiaceae)

Abstract Interspecific interactions involving ants range from antagonistic to mutually beneficial, depending on the context. Myrmecophytic Macaranga trees form symbiotic associations with ants, whose aggressive behavior protects the trees against herbivorous insects. Nevertheless, galls induced by cecidomyiid midges still occur on these myrmecophytes. We hypothesized that the midge larvae or pupae that form their galls on Macaranga myrmecophytes can exploit the enemy‐free space provided by the ants, which continuously patrol the myrmecophytes. To test this hypothesis, we conducted a field survey of the galls of Schizomyiina sp. 2 on the leaves of M. beccariana in a Bornean rainforest. We found that the mean number of galls of Schizomyiina sp. 2 on a leaf and the parasitism rate of the midges by parasitoid wasps were significantly higher on trees without ant protection than on trees with ant protection. These results support our hypothesis and suggest that enemy‐free space indirectly provided by ants is an important benefit of using myrmecophytic plants for herbivorous insects, even though they must incur the cost of becoming immune to the ants' aggression.