Home sweet home: Evaluation of native versus exotic plants as resources for insects in urban green spaces

Abstract

Abstract Insect decline and loss of biodiversity not only affect large‐scale agricultural landscapes, but are increasingly recognized in urban environments. It is undisputed that a greater supply of flowers in urban green spaces can provide insects with more food and habitat. However, it is still controversial whether native wild plants or non‐native ornamental plants and varieties are the right choice. To answer this question we investigated the number of insects interacting with different types of plants: twelve ornamental and six related wild perennials. In this context, the number of flower visitors per plant species and plot was recorded at 10‐minute observation intervals, as well as the feeding damage caused by insect herbivores on the leaves and stems of the study plants. We established 18 plant species in ten independent study plots in the city of Darmstadt, Germany. The plants were six native wild plant species, six ornamental plant species related to the wild plants from the same genus or family and six exotic ornamental plant species from other genera and families than the wild plants. Native insects (wild bees, flies, beetles, wasps) that feed on pollen and nectar visited wild perennials significantly more often (67% of all visits) than related ornamental (24%) and unrelated exotic plants (9%). In contrast, honey bees (Apis mellifera) showed no preferences to any of the three target plant groups and interacted with other plant species than most of the native insects in our study according to analyses of interaction networks. The assessment of leaf damage caused by insect herbivores on the individual plants confirmed a similar and significant difference in the insects' choices. Leaves from wild plants showed the highest herbivory (mean 2.3% of the leaf area), followed by related ornamental plants (0.8%), whereas unrelated exotic plants were hardly consumed (0.1%) by herbivores. Practical implication. Our study shows that in urban green spaces, both flower‐visiting and leaf‐feeding insects are more likely to use native wild plants as a food source than closely related and exotic ornamental plants.

Keywords

• biodiversity
• herbivores
• honey bee
• insects
• leaf damage
• native plants