Weeds for bees? A review

Abstract

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 seminatural 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.

Organic fields sustain weed metacommunity dynamics in farmland landscapes

“…Improving such habitats may have a lower effect on crop production (i.e. less frequent species are in field margins and are rarely abundant in the field core), but may support other ecological services such as pollination [26,79,80]. Our results also suggest that biodiversity and crop production may be supported in landscapes with less intensively farmed fields according to a land-sharing strategy, although further studies incorporating weed abundance (rather than just richness) need to be conducted.…”

Weed-insect pollinator networks as bio-indicators of ecological sustainability in agriculture. A review

“…The decrease in some weeds may be due to the intensive use of external inputs (Marshall et al 2003;Bretagnolle and Gaba 2015). This can be direct effects on weeds (e.g., herbicides, fertilizers) or indirect effects on their pollinators (e.g., insecticides).…”

“…They play major functional roles for agricultural ecosystems and their biodiversity and thus have several consequences on ecosystem services, especially pollination (Biesmeijer et al 2006;Bretagnolle and Gaba 2015). Increasing weed abundance can (i) maintain pollinator populations, (ii) ensure pollination services, (iii) increase honey yields and therefore be a benefit for beekeepers, and (iv) improve the sociocultural value of landscape by ensuring the persistence and survival of wild flora (Bretagnolle and Gaba 2015). For instance, some studies have showed the importance of weeds as food resource for insect pollinators, especially bees (Rollin et al 2013;Requier et al 2014).…”

“…In addition, several concerns have been raised regarding the decreased plant and pollinator biodiversity in different ecosystems, focusing on the possible relation between the rarefaction of some plants and their dependence on particular insect pollinators (Benvenuti 2004;Gibson et al 2006;Nicholls and Altieri 2012;Grass et al 2013). The decline in wild bee diversity has been strongly correlated with the decline in wildflowers (Biesmeijer et al 2006;Bretagnolle and Gaba 2015 for a recent review).…”

“…2) and solitary bees dominate. In Mediterranean arable lands, Andrenidae, Apidae, Colletidae, Halictidae, Megachilidae, and Melittidae are the main species of solitary bees (Bosch et al 1997;Dicks et al 2002;Petanidou and Lamborn 2005;Bretagnolle and Gaba 2015). However, some species of the Halictidae (Halictus and Lasioglossum particularly, e.g., Lasioglossum malachurum (Kirby), Lasioglossum pauxillum (Schenck), Halictus rubicundus (Christ)) are eusocial (Michener 2007) and can be locally dominant and abundant wild bee species (Rollin et al 2015).…”