Vehicle pollution elevates insect herbivory on urban trees

Background/Question/Methods

Vehicle pollution is a pervasive aspect of anthropogenic change in both urban and rural habitats. Plant-insect herbivore interactions are highly contingent on environmental variables associated with pollution, including the availability of carbon and nitrogen in leaves. Nitrogen- and carbon-based compounds are emitted from tailpipes, but the extent to which these compounds are then taken up by plants is poorly understood, as are any downstream effects on insects that feed on plants in polluted environments.

Results/Conclusions

Here, we demonstrate that herbivory on commonly planted oak trees (Quercus lobata) across the state of California is substantially elevated on trees planted within 200 meters of highways compared urban trees further from highways and rural trees. In the laboratory, caterpillars preferred leaves from highway adjacent trees and performed better on leaves from highway adjacent environments. Together, our data suggest that pollution associated with highways affects interaction strengths and may explain highly variable patterns of insect feeding within cities. While planting trees near highways may provide benefits to residents, tradeoffs between these benefits, tree health, and insect conservation should be considered in tree planting programs as the climate warms and trees are exposed to multiple increasing stressors.