Pollinator diversity on roadsides and traffic related impacts

The diversity and abundance of wild pollinators are declining. One of the primary drivers behind this decline is the fragmentation of their habitat. Roads are significant to this fragmentation, acting as potentially lethal physical barriers. As part of the Safeguard project, our research focuses on the effects of road traffic on pollinators. In Western Europe, roads are omnipresent, and cars remain citizens' favored mode of transport. Our study compares two countries, Belgium and Serbia, each characterized by distinct road densities. Belgium boasts a road network eight times denser than that of Serbia.
Our study initially investigates the diversity of bees, hoverflies, and butterflies along roadsides to assess their ecological quality. We then examine the attractiveness of plants to these pollinator groups to provide recommendations for land-use planning. Additionally, we will evaluate whether flowering roadsides act as honey traps for pollinators in general. Finally, we will analyze the bee, hoverfly and butterfly communities impacted by the risk of collision.
We are conducting line-transect sampling along roads with heavy and light traffic in agricultural and semi-natural landscapes to answer these questions. A total of 24 sites in Belgium and 24 sites in Serbia are sampled three times. During each survey, bees, hoverflies, and butterflies are net-sampled along roadsides. Floral species and their coverage are assessed using a 1-square-meter quadrat. Additionally, roadside sampling is conducted using a sticky trap installed under the vehicle's license plate.
The results of our study are as follows: The diversity of pollinators, particularly bees, is low along roadsides, which can nevertheless host endangered species. An interesting result of our study in Belgium reveals that pollinator species richness is significantly higher along minor roads than along major roads, with 66% more bee species, 76% more hoverfly species and 46% more butterfly species on low-traffic roadsides. This pattern is not observed in Serbia, likely due to the lower density and use of the Serbian road network. Concerning plant attractiveness, Cirsium arvense and Carduus acanthoides are the most attractive flowers for bees in both Belgium and Serbia. They are also among the preferred plants for Belgian hoverflies and butterflies in Belgium and Serbia. We have not identified floral roadsides as honey traps for pollinators. Thysanoptera, Diptera, and Hymenoptera are the insect orders most frequently hit by vehicle collisions in both countries. Within the primary pollinator groups, bees, hoverflies, and butterflies were few killed by vehicle collisions, whereas smaller insects were more dominant.