Realising multiple ecosystem services based on the response of three beneficial insect groups to floral traits and trait diversity

Beneficial insects in agro-ecosystems provide humans with many invaluable ecosystem services including crop pollination and pest control. The creation of wildflower strips has emerged as a key tool to conserve beneficial insect groups in these systems. Yet, the efficacy of these schemes in delivering multiple ecosystem services is usually limited by our poor understanding of how plant species composition, functional traits and trait diversity affect insect visitation and resource use. Here we investigate the effects of plant floral traits and trait diversity on flower visitation by three functionally distinct beneficial insect groups, which provide crop pollination and pest control services: bumblebees, hoverflies and parasitoid wasps. We created plots that contained plants with either long or short-corolla flowers, as well as mixed plots, which contained plants presenting both floral traits concurrently. In functionally simple plots, insect groups exhibited distinct floral associations, with bumblebees being almost exclusively associated with long-corolla flower plots, whereas parasitoids and hoverflies strongly favoured plots with short-corolla flowers. When these flower types were planted in combination (mixed-trait plots), bumblebee and hoverfly visitation was maintained at the level of their respective preferred single-trait plot, but parasitoid visitation was reduced by 50%. Thus, the informed selection of functionally diverse flower patches can be an effective tool to attract a higher diversity of insect groups than functionally simple plots. However, this may increase interference competition between visitors and limit the value of floral resources for beneficials that are weak competitors.