Grass management intensity affects butterfly and orthopteran diversity on rice field banks

Agricultural intensification through landscape homogenization has been identified as one of the main drivers of the recent biodiversity decline in European farmlands. In particular, the loss of non-cropped habitats has often deprived farmland species of feeding and nesting sites, refuge areas, and dispersal corridors. In this framework, well-managed field margins may play a key role for wildlife conservation in agroecosystems, providing additional suitable habitat patches for many species, which also include several natural agents of pests' biological control. In rice crops, paddy banks are usually heavily managed by farmers, which remove vegetation through chemical or mechanical procedures, with a consequent limitation of the potential role of levees in maintaining a functional agroecosystem. The aim of this study was to investigate the response of butterfly and orthopteran diversity to different grass management practices on rice field banks, namely herbicide spraying, mowing, and no management. Between April and September 2016, we sampled butterflies and orthopterans on 30 and 22 paddy levees respectively, located in three sites within the intensive rice crop district of northern Italy. Herbicides spraying proved to be the most detrimental practice for these insects, producing a considerable reduction in species richness and abundance in comparison with unmanaged and mown banks. The impacts of mowing were less pronounced than those of chemical treatments; however, frequent cutting caused a significant reduction in butterfly and orthopteran diversity on levees. Our results highlight the importance of unmanaged banks in preserving insect diversity in rice crops, while herbicide spraying should be avoided. Low frequency and rotational mowing could represent sustainable management solutions to meet biodiversity and husbandry requirements in this agroecosystem.