Weeds for bees? A review

Agricultural intensification has led to the decrease of the diversity of wild and domestic pollinators. For instance, honeybees declined by 59 % in 61 years in the USA. About 35 % of major crops in the world depend on pollination services, and 3-8 % of world crop production will disappear without pollinators. Indeed, pollination provides several ecosystem services such as enabling crop and honey productions, regulating weeds and other cultural services. Agricultural intensification has also decreased weed diversity by about 50 % in 70 years because massive herbicide sprays have reduced the competition between weeds and crops. Nevertheless, weeds are at the basis of agricultural foodwebs, providing food to many living organisms. In particular, weeds provide flowers for pollinating insects including honey and wild bees. Here, we review the decline of weeds and bees. We discuss the effect of bees and pollination on crop production. We describe the complex interactions between bee pollinators, e.g. honey and wild bees, and landscape habitats such as crop fields and semi-natural elements. For that, we focus on spatial and temporal effects on flower resources. We show that weed abundance can reduce crop yields, thus inducing conflict with farmers. But weed abundance enhances regulating services by ensuring the survival of honeybees in the absence of oil seed crops. Weed abundance also enhances pollination services and, in turn, honey yield for the benefit of beekeepers. Weed abundance has also improved the survival of wild flora and the socio-cultural value of landscapes, a major request from the public. From those findings, we present a conceptual framework allowing to define ecological engineering options based upon ecosystem services of weeds and pollinators.