Hellerich, C. | Search bioRxiv

bioRxiv2026

Annual ploughing turns wildflower plantings into ecological traps for ground-nesting wild bees

Wildflower plantings are an important conservation measure for supporting wild bee diversity. They aim to enhance floral resources for nutrition, but do not explicitly consider that bees also require suitable nesting and overwintering resources. Wildflower plantings may provide nesting habitat for ground-nesting bees, but the effects of soil management, e.g. ploughing, on ground-nesting bees are hardly known. To study how ploughing and age of wildflower plantings affect ground-nesting bees, we sampled bees on ploughed and unploughed wildflower plantings aged 0-4 years. We used emergence traps to sample bees directly after emergence from the ground, allowing inference on nest numbers. We found that ploughing and wildflower planting age negatively affected overwintering bee nest numbers. Nesting peaked in the year of wildflower planting establishment and declined thereafter, indicating lower habitat suitability at later successional stages. Annual ploughing caused the greatest reduction in nest numbers (-72 %), providing evidence for an ecological trap.

ecology↗

bioRxiv2025

Reducing ploughing promotes ground-nesting flying insects

Many flying insects, such as bees, wasps, and hoverflies, live aboveground, but depend on soil for nesting, development, and overwintering. In agricultural landscapes, soil is managed for production and therefore frequently subjected to disturbances such as ploughing. The impacts of ploughing on flying insects that spend part of their life cycle belowground remain largely unknown. To investigate the effects of ploughing on ground-nesting flying insects, we conducted a two-year field experiment in flower strips subjected to different treatments, ranging from annual ploughing to four years without ploughing. Insects emerging from the soil were sampled using emergence traps, allowing a direct assessment of their response to ploughing at different frequencies. For each treatment, we measured insect biomass, abundance, and body size. We found that ploughing substantially reduced flying insect biomass. When sites were left unploughed, biomass increased rapidly, particularly during the first years of recovery. However, regardless of the time since the last disturbance, ploughing always reduced insect biomass to similarly low levels, driven primarily by declines in the abundance of large insects. Our findings highlight that even moderate reductions in ploughing frequency, for example, only every second year, can benefit ground-nesting flying insects and point to the potential for incorporating reduced ploughing frequencies into agricultural management and agri-environmental schemes.

ecology↗