Weeds from non-flowering crops as potential contributors to oilseed rape pollination

Pollination is essential for many crops since 70% of the world's cultivated plants depend on pollinators for their production. Floral resources within cultivated areas, especially those produced by flowering crops such as oilseed rape, are known to have a positive effect on wild pollinators. Nevertheless, little is known about the contribution of other floral resources, such as weeds within cultivated areas, in supporting wild pollinator communities and subsequent pollination services. Here, we investigate the extent to which oilseed rape pollination benefits from floral resources produced within cultivated areas, either crops or associated weeds. Based on the Müller index, we analyzed, during four pairs of consecutive years, the potential for inter-annual indirect effects received by oilseed rape through shared wild pollinators from major crops, and their associated weeds, in a typical French intensive agricultural landscape. Our results show that most of the support for oilseed rape pollinating fauna came from alternative types of floral resources than itself. We also find that weeds support oilseed rape pollination as much as flowering crops. Finally, we show that weeds growing within cereal fields have a major contribution to the support of oilseed rape pollination, exceeding the contribution of other floral resources, except oilseed rape. Our results underline that oilseed rape pollination benefits from floral resources present within cultivated fields, whatever the type of crops, including those that do not depend on pollinators for their pollination. Management practices like herbicide reduction in non-pollinator-dependent crops such as cereals are thus likely to impact the pollination of pollinator-dependent crops. •Inter-annual networks reveal dependence of crop pollination to past floral resources.•Weeds as important as flowering crops for oilseed rape pollinators.•Weeds in cereal fields are major floral resources for oilseed rape pollinators.