Road-associated variation in insect abundance differs between common orders

Abstract The ecological impacts of roads are well-researched for many vertebrates, but studies are relatively lacking with regards to invertebrates. Here, we document changes in the abundance of ground-dwelling species of the three most common insect orders, Hymenoptera (specifically ants), Hemiptera (true bugs) and Coleoptera (beetles), with distance from a gravel road in a grassland system in South Africa. Insects were collected by means of 164 pitfall traps installed at 2, 5, 10 and 20 m perpendicular to a gravel road, and abundances of these three orders were compared statistically between the four distances. Whereas no differences in the numbers of Hymenoptera and Coleoptera were observed with distance from road, the abundance of Hemiptera was greater closer to the road. Although contrary to our initial expectation, this finding is in line with previous studies, which explore changes in plant chemistry and reduced predator efficiency next to roads as possible mechanisms. We conclude that not only busy, high-traffic roads should be taken into account in roadside ecological studies on insects, but that quieter, low-traffic roads should also be considered, as these can also affect the distribution of species at finer spatial scales.