Flower visitor observations
Observations were carried out between July 2nd-10th at appropriate weather conditions (warm, sunny, dry). One m² of each plot was observed for 15 min. Due to time limitations and withering of linseed, only one replicate out of four could be observed twice. We assessed numbers of flower visits and flower visitor species (if possible, orders otherwise), on monocultures of wheat, faba bean and linseed, their two- and three-species mixtures and control plots where no crop was sown, but where weeds established (Table S9). We recorded which plant species was visited for both crops and weeds for each plot and counted every contact with floral organs as one visit. When the ears of wheat plants were visited, this was also counted as a flower visit, as it has been shown that hoverflies and bees also visit wind-pollinated plants (Saunders 2018). For data analyses, we summed all observations per crop diversity (four levels, see Staab et al., 2015) and per crop mixture (eight levels).