The influence of management and land use diversity at local and landscape scales on communities of generalist predators in commercial dessert apple orchards

Abstract

This study explored the combined influences of land use diversity, chemical pest management and grass alley management on the abundance of two key predatory taxa which act as natural enemies of pests in UK commercial dessert apple orchards, namely ground beetles (Coleoptera: Carabidae) and the European Earwig Forficula auricularia (Dermaptera: Forficulidae). Carabid and earwig numbers were positively related to higher predation levels; however, each was affected differently by land use diversity. Land use factors were not related to carabid activity-density but were related to community composition and the representation of traits in the community. Higher proportions of larger, polyphagous species and fewer spring breeders were observed in more diverse land use settings, while adjacent land use was found to influence diurnal activity and habitat associations. The proportion of polyphagous carabids in the assemblage was in turn found to be related to increased predation. Earwigs were not affected by land use diversity in isolation at either scale, though an interaction between adjacent land use and distance into the orchard was observed, indicating a distance mediated effect of non-crop habitats on earwig numbers. Earwig abundance was positively related to increased predation. Use of the neonicotinoids flonicamid and thiacloprid was associated with declines in the numbers of carabids and earwigs, with thiacloprid use also associated with a number of other carabid community metrics. Chlorpyrifos was associated with greater activity-density of carabids, but lower functional diversity. Earwig numbers did not appear to be affected by chlorpyrifos use under the field conditions employed here. Both a reduction in the frequency of mowing and raising the height of mower blades led to increases in the abundance of epigeal predators in a study orchard. In contrast, arboreal predator communities were not affected by the mowing treatments applied. The work presented here clearly demonstrates that generalist natural enemies found within commercial dessert apple orchards are influenced by both the adjacent land use and the diversity of the surrounding land use at a landscape scale. Farm management and chemical pest control have also been shown to affect orchard natural enemy communities. These findings show that both carabids and the European earwig have the potential to contribute to natural pest control in orchards. Further, this work may explain some of the variation observed in earwig populations between orchards. The provision of non-crop habitat, reductions in chemical use and vegetation management could be employed to enhance these natural enemy communities in commercial dessert apple orchards.