Parasitism of the beech leaf‐miner weevil in a woodland: patch size, edge effects and parasitoid species identity

Abstract

Abstract. Deciduous woodlands are a key habitat for the diversity of invertebrates within the primarily agricultural landscape of lowland Scotland. Little is known, however, of the contribution that within‐site heterogeneity plays in maintaining invertebrate diversity within these habitats. We consider how habitat heterogeneity affects the beech leaf‐mining weevil, Rhynchaenus fagi L. (Curculionidae, Coleoptera), and its associated polyphagous parasitoids. This was carried out by investigating host density and parasitism rates of the weevil as it fed on 88 beech trees Fagus sylvatica L. (Fagaceae) occurring in patches within a birch woodland. We aimed to assess how patch site, isolation and patch quality influenced parasitism rates and parasitoid diversity. Herbivore leaf‐mine abundance was greatest where beech trees were located on the edge. Parasitism rates were also affected by the location of the host insect at the woodland edge and interior. Depending on parasitoid species identity, parasitism rates showed independent, direct, and inverse responses to the density of leaf mines. Parasitism rates showed direct and inverse responses to the patch sizes of beech trees, while overall parasitoid diversity was negatively correlated with patch size. Heterogeneity in the location of the beech trees within this birch woodland plays a key role in determining local patterns of parasitism rates and parasitoid diversity. It is suggested that within‐site variation in the area of high quality resource patches, represented by the beech trees, was key to structuring these parasitoid communities. Niche separation was promoted by individual species’ capacity to locate host insects in this spatially complex habitat.