Insect pollination enhances faba bean yield more than weed removal or fungicide application

Insect pollinators provide important crop pollination services but are declining in response to lack of diverse flower resources and exposure to pesticides. Despite increasing evidence that the benefits of insect pollination for crop production depend on other ecosystem services and crop management practices, investigations have mostly been limited to how pollination benefits are affected by insect pest control and soil fertility levels. Here we used a factorial cage experiment in the field to test how pollination by bumble bees, manual weed removal and fungicide application interactively shape faba bean (Vicia faba) yield components, and how weed removal and fungicide application affect bumble bee foraging behaviour. We found that insect pollination and weed removal increased faba bean yield components mostly additively, with insect pollination being the most important factor to maximise yield. The fungicide treatment did not affect crop yield, probably due to the low fungal pathogen incidence in the experiment, but instead affected bumble bee visitation behaviour. Bumble bees visited flowers of fungicide-sprayed plants more often than fungicide-free plants. This has potential consequences on bee health that should be further assessed. Guidelines on pesticide use should be improved by weighing benefits to agricultural productivity against risks for pollinators according to integrated pest and pollinator management principles. Our results emphasise that insect pollination can be an important factor for crop yield. The additive benefits of insect pollination and weed removal to crop yield indicates that they are crop production factors which can be managed for independently.