Flying insect abundance declines with increasing road traffic

Abstract

Abstract One potentially important but underappreciated threat to insects is road mortality. Road kill studies clearly show that insects are killed on roads, leading to the hypothesis that road mortality causes declines in local insect population sizes. In this study we used custom‐made sticky traps attached to a vehicle to target diurnal flying insects that interact with roads, sampling along 10 high‐traffic and 10 low‐traffic rural roads in southeastern Ontario, Canada. We used a paired sampling design to control for potentially confounding differences in the road characteristics (e.g. road width) and surrounding land covers (e.g. housing density) between high‐traffic and low‐traffic roads. We then used these data to test the prediction that fewer flying insects collide with vehicles, per vehicle (i.e. insect abundance is lower), on high‐traffic than low‐traffic roads. We found significantly fewer insects at the high‐traffic roads than at the low‐traffic roads as predicted. There was a 23.5% decline in the number of insects/km/vehicle on high‐traffic relative to low‐traffic roads. Given the high rates of insect mortality observed in previous studies, it is likely that road mortality contributes to these observed negative effects of traffic intensity. Thus the growing global road network is a concern for conservationists and land managers, not only because insect population declines contribute to the ongoing global losses of biodiversity but also because insects play a vital role in food webs and provide important ecosystem services.