Assessing the contribution of lawns and semi-natural meadows to bee, wasp, and flower fly communities across different landscapes

Land conversion and intensive vegetation management are major drivers of shifts in insect communities, including economically valuable species. We evaluated the impact of lawns and meadows across agricultural, residential, and industrial landscapes in structuring bees, wasps, and flower flies communities. We carried out plant and insect inventories on 18 lawns and 18 meadows distributed evenly among agricultural, residential, and industrial landscapes within the Greater Quebec City region (Quebec, Canada). Insect sampling was conducted five times using bowl traps and entomological nets, from June to September 2020. Results indicate taxon-specific responses to landscape matrix and site maintenance. Agricultural landscapes negatively influenced bee abundance compared to urban areas, while the opposite trend was observed for flower flies. Wasp abundance and richness were negatively influenced by both agricultural and industrial matrices compared to residential landscapes. Regarding site maintenance, bees and wasps were 3 and 12 times more abundant and 2 and 6 times more species-rich, respectively, in meadows than in lawns as per the data aggregated across the sampling date. Flower fly abundance was higher in meadows than in lawns for agricultural and residential landscapes only, while richness was consistently higher (2 times greater) in meadows compared to lawns. Some species of the sweat bee genus Lasioglossum and the flower fly margined calligrapher (Toxomerus marginatus) were dominant in lawns, while meadows hosted a more balanced community among genera and supported pollinators with wide-ranging resource requirements. Our results suggest that conservation actions should consider both landscape and local management to conserve central-place foragers, such as bees and wasps, and for structuring flower fly species composition.