Rich assemblages of native pollinators profit from flowering strips with lacy phacelia (Phacelia tanacetifolia) and from monocultures of this plant

The cultivation of flowering strips on arable land is one way to support the nonproductive functions of agriculture, including strengthening the conservation of pollinators in the landscape. Despite this, a comprehensive assessment of the ecological benefits of such measures and their importance for pollinating insects is still lacking. Therefore we investigated the effects of lacy phacelia on pollinator communities and annual mixed stands in which lacy phacelia was one of the plant components. The research was carried out in 28 monocultures of lacy phacelia and 28 flowering strips with lacy phacelia proportions in the Czech Republic. At each site, within a defined transect, we conducted netting of bees and wasps, hoverflies and butterflies. Both monocultures and mixed stands attracted a wide range of species. The species diversities and abundances of most of the pollinator groups studied were greater in mixed stands, where butterflies and non-aphidophagous hoverflies were significantly more numerous and diverse. Lacy phacelia flowers were mainly visited by common, nonspecialized insects, whereas mixed stands were more attractive to a greater number of specialists. Our findings therefore point to the significant benefits of flowering strips including lacy phacelia for pollinating insect communities in agricultural landscapes, and we recommend the support of flower strips including lacy phacelia in EU agri-environment schemes. We additionally draw attention to the importance of a detailed understanding of pollinator relationships in a landscape context and highlight the need for further studies to contribute to the design of additional functional measures for biodiversity conservation in agricultural landscapes.