Biocontrol in Urban Ornamental Landscapes: Does Plant Geographic Provenance Matter?

Urban ornamental landscapes tend to be mosaics of native and exotic plants. Although there has been renewed interest in effects of the provenance of plants in the landscape on pests and other herbivores inhabiting them, little attention has been paid to its effect on arthropod natural enemies and biocontrol of pests. In eastern North America, commonly grown exotic woody plants had been missing from the continent for between one and tens of millions of years until the arrival of Europeans. Due to the lack of a recent co-evolutionary history with exotic plants, native natural enemies should be less well able to utilize the resources – architecture and nutritional supplements – provided by those plants than they would those of native plants, hence less numerous and diverse in landscapes dominated by exotic plants. We test this hypothesis in a replicated experiment comprising 0.2 Ha plots planted to congeners of 15 genera of woody plants from either Eurasia or North America, grown in a turf of tall fescue. Adult hymenopterous parasitoids collected by vacuum sampling from the turf were statistically less abundant and less diverse in the exotic plots, supporting the hypothesis.