How many species are there in apple insect communities?: testing the resource diversity and intermediate disturbance hypotheses

Abstract

Abstract. In European and American apple orchards the insect species richness, calculated from our own, and published data, varied widely (30–940 species). The dominance of insect orders was similar to that found in natural communities. To test the predictions of the‘resource diversity hypothesis’(RDH) and the‘intermediate disturbance hypothesis’(IDH) of insect diversity, we analysed the simultaneous impact of vegetational diversity and intensity of orchard management practice on the species richness of characteristic insect categories in six types of apple stands, over 5 years, in Hungary. The more diverse was the vegetation adjacent to the orchard and the less intensively was the orchard managed, the greater was the total insect species richness, supporting both hypotheses. The number of agricultural pest species found in the apple orchards depended above all on the diversity of adjacent agricultural vegetation, supporting only the RDH. The species richness of specialized apple pests was limited only by the intensity of pest control, supporting only the IDH. Within the category of generalist natural enemies species richness mainly varied with the diversity of adjacent vegetation, supporting the RDH. The aeroentomofauna constituted a surprisingly high percentage (>50%) for both total species and agricultural pests, but was poorly represented within the natural enemies category, and absent from the specific apple pest category. A general conclusion is that the number of insect species in perennial orchard‐systems within agricultural areas is determined primarily by the regional extra‐orchard vegetational diversity and secondly by the degree of local intra‐orchard disturbances and plant diversity. Consequently, at the community level the predictions of both hypotheses can be simultaneously valid at different spatial scales and are not mutually exclusive. However, within the community, at the level of the different insect categories studied here, only one of the hypotheses proved to be valid.