Pollinator emerging from extensive green roofs: wild bees (Hymenoptera, Antophila) and hoverflies (Diptera, Syrphidae) in Geneva (Switzerland)

Abstract

By the end of 2020, 75% of the Swiss population will live in cities. The urban densification will result in habitat and biodiversity loss. One solution to mitigate this loss in urban environments is the implementation of green roofs that are now recognised as a tool for the maintenance of epigeal and aerial arthropods. Green roofs can provide various services such as pollination and food supply for insects and various arthropods (e.g. arachnids) and animals (e.g. birds). The objective of this study was to evaluate the diversity of pollinating insects emerging from urban green roofs. Wild bees (Hymenoptera) and hoverflies (Diptera) were sampled using emergence traps on six extensive green roofs in the urban area of Geneva (Switzerland), from March to August 2017. Five species of wild bees and two species of hoverflies were identified: Lasioglossum morio (Halictidae) and Sphaerophoria scripta (Syrphidae) are the only two species considered as emerging from green roofs in our study. Ecological traits of these two species indicated generalists, well adapted to xero-thermophilic conditions.