Does traffic intensity affect insect communities? Impact on pollinator mortality

Population decline trends among pollinators have become a major global concern in recent years. Many action plans and strategies have been launched to assess the causes and consequences of the global decline in insect pollinators. Road construction presents an increasing threat to pollinators by directly contributing to habitat fragmentation. Additionally, pollinators face risks from road traffic. This study aimed to contribute to our understanding of the impact of traffic on the abundance of insects (due to direct collision) and examine the differences in their presence between minor and major roads, focusing on two groups of pollinators—bees and butterflies. Insects were examined at 24 localities in northern Serbia during three seasons in 2023, along two types of roads (12 minor and 12 major road types) within areas dominated by either agricultural or semi-natural habitats. To measure the direct insect mortality caused by traffic, sticky traps measuring 10cm x 25cm were attached to a car, which was driven along the 1.25km stretch of road in both directions at a constant speed of 60km/h. A total of 476 insect specimens were documented on sticky traps, including only six bees and two butterflies. Hymenoptera, especially parasitoid wasps, were the insects most affected by traffic, accounting for up to 25% of the total number of insects caught on traps. These findings suggest that traffic may have a greater effect on the mortality of smaller insects. Insect counts were 14% higher on sticky traps on minor roads compared to major roads, with 75% of targeted pollinators recorded on minor roads. Our results show that more insects were recorded on minor roads within semi-natural landscapes than on major roads within agricultural landscapes. However, the low number of pollinators on sticky traps suggests that direct traffic does not significantly affect bee and butterfly mortality.