Wild plants in hedgerows and weeds in crop fields are important floral resources for wild flower-visiting insects, independently of the presence of intercrops

Abstract

The availability of diverse floral resources is crucial for the maintenance of pollinating insects and the pollination service they provide in agricultural landscapes. Ensuring plant diversity is thus essential for the maintenance and even restoration of pollinator communities. Many studies have highlighted the beneficial effects for pollinating insects of the floral resources provided either by uncultivated plants in agroecological infrastructures such as hedgerows and in crop fields, or by the addition of cultivated flowers through intercropping. However, the role of these different co-occurring vegetation types in providing floral resources to wild flower-visiting insects remains unexplored simultaneously, especially regarding their potential interacting effects. Using a paired design sampling approach, we investigated the contribution of floral resources provided by hedgerows, weeds in crop fields, and legumes intercropped with winter cereals, and their interacting effects, to the abundance of different groups of wild flower-visiting insects, plant-insect interactions and insect preferences. Our results show that the abundance of most groups of floral visitors were enhanced by the cover or species richness of floral resources provided by hedgerows or by weeds in crop fields. Interactions between uncultivated plants and insects were driven by the presence of some particular ‘preferred’ plant species offering either abundant, accessible or high-quality floral resources. By contrast, abundance of floral visitors was not enhanced by the addition of legume flowers through intercropping. The positive effects of flowering wild plants in hedgerows and crop fields remained mostly unchanged in the presence of intercrops, because of the limited contribution of legumes in providing attractive floral resources to floral visitors. Our results highlight the critical role of floral resources provided by weeds in crop fields for diverse flower-visiting insects, in addition to the floral resources provided by hedgerows. We recommend that agri-environment schemes should promote a wide diversity of floral resources at field margins through the retention of existing semi-natural elements or the sowing of wildflower mixtures. More importantly, our study encourages the seeking of alternative forms of weed management, which support a trade-off between the maintenance of pollinating insects and pollination service provision on the one hand, and crop yields and incomes for farmers on the other.