Intercrops as foraging habitats for bees: Bees do not prefer sole legume crops over legume-cereal mixtures

Enhancing crop diversity is an option to make agriculture more sustainable and biodiversity friendly. Intercropping grain legumes together with cereals leads to higher crop diversity and has a broad range of agronomic and ecological benefits. However, sole crop stands of grain legumes might be richer in floral resources than grain legume-cereal intercrops and thus are probably more useful to mitigate the lack of flower resources in agricultural landscapes, which is a main driver of pollinator decline. Yet, little is known about differences between both cropping systems and different legume genotypes in terms of attractiveness for pollinators and how these differences moderate the pollinators’ foraging behavior and consequences for grain legume yields. In a field trial, we analyzed the abundance of flower visiting insects, the foraging behavior of pollinators and related effects on grain yield per plant across six different faba bean genotypes (Vicia faba L.) grown as sole crops or as intercrops with wheat. As foraging behaviors, we considered legal flower visits (i.e. frontal visits) and illegal flower visits (i.e. nectar robbing through bite holes). We recorded characteristics of V. faba genotypes on crop stand level (V. faba plant height, number of V. faba inflorescences and leaf area index (LAI)). V. faba-wheat intercrops and sole crop stands of V. faba were equally attractive foraging habitats for pollinators, implying that intercrops are as suitable as sole crops to mitigate the lack of floral resources. Yield per V. faba plant was positively affected by bee pollination, with this effect being determined by the number of illegal flower visits, suggesting that this foraging strategy does not adversely affect V. faba yields and even has a positive effect. Intercrops had higher yields per V. faba plant than sole crop stands of V. faba, indicating agronomic advantages of this farming practice. Although V. faba genotypes differed in their plant traits, these differences could not explain shifts in the number of flower visiting insects. However, illegal flower visits increased with a higher number of inflorescences whereas the number of legal flower visits declined. Based on our small-scale experiment, we conclude that the use of V. faba-wheat intercrops brings agronomic benefits while serving as a foraging habitat for pollinators that proved to be as attractive as sole crop stands of V. faba.