Abstract
Non-crop habitats are important to support biodiversity and ecosystem services in agricultural landscapes. Whereas perennial and managed non-crop habitats have known benefits, temporary non-crop patches within arable fields (field defects) have been poorly studied.
We created artificial field defects (unsown patches) in oilseed rape (Brassica napus L.) fields and evaluated their effects on parasitoid assemblages at two crop growth stages. Moreover, we compared unmanaged patches with those sown with flowering plants (Onobrychis vicifolia) and crop controls and analyzed the influence of position within the field (edge or interior), and total flower availability.
Altogether, we found almost 200 morphospecies of hymenopteran parasitoids (140 in unsown patches, 147 in Onobrychis patches, and 81 in controls), including important enemies of crop pests. Species richness and abundance were higher on both types of unsown patches than in controls but were not affected by Onobrychis sowing.
The differences between unsown patches and controls were larger during oilseed ripening, suggesting that these temporary habitats can offer important resources during crop senescence. Parasitoid species composition differed between controls and unsown patches, indicating that species not linked to the crop could also benefit from these habitats.
Finally, unsown patches with higher flower availability supported higher species richness, total abundance, and abundance of three key species during OSR flowering. Thus, newly created unmanaged habitats have the potential to increase biodiversity despite their small size, although increasing flower resources can boost their benefits.
Unsown patches can be easily created by switching-off sowing, facilitating their adoption by farmers. Future studies on pest control levels and comparisons with other agri-enviromental schemes would help to elucidate the cost-benefit of unsown patches.