The attractiveness of flowering herbaceous plants to bees (Hymenoptera: Apoidea) and hoverflies (Diptera: Syrphidae) in agro-ecosystems of Central Spain

Habitat management, with the aim of conserving pollinators in agro-ecosystems, requires the selection of the most suitable floral species in terms of their attractiveness to pollinators and a simplicity of agronomic management. A randomized block design including 12 herbaceous plants was used to study their attractiveness to pollinators (insect visitation), their attractiveness efficiency (a combination of duration of flowering and insect visitation), their response to two different agronomic management practices (growing in mixed versus mono-specific stands; tillage versus no-tillage) and their potential weediness. The flowers of Borago officinalis, Echium plantagineum, Phacelia tanacetifolia and Diplotaxis tenuifolia were attractive to bees, whereas Calendula arvensis, Coriandrum sativum, D. tenuifolia and Lobularia maritima were attractive to hoverflies. A floral mixture resulted in a lower attractiveness efficiency to pollinators than D. tenuifolia, but higher than when compared with most of the mono-specific stands. On the other hand, although some of the most attractive plant species (P. tanacetifolia and C. arvensis) showed potential weediness, their self-seeding was reduced by tillage treatment. Diplotaxis tenuifolia was the only plant with a high attractiveness efficiency to pollinators and efficient self-reproduction. Therefore, D. tenuifolia is highly recommended species for attracting bees and hoverflies in agro-ecosystems of Central Spain.