Inhospitable hosts: Diminished herbivory, abundance, and success of caterpillars on invasive shrubs in eastern North America

Caterpillars are the dominant arthropod herbivores in many ecosystems, including the woodlands of eastern North America. These abundant and diverse insects are crucial to ecosystem functions as both herbivores and prey. Throughout their shared history, caterpillars and plants have been locked in an evolutionary arms race. However, native caterpillars and exotic invasive plants have not had the opportunity to coevolve. Consequently, native caterpillars may struggle to colonize these novel hosts. In this study, we assessed the degree to which invasive plants support native caterpillar communities. We did so by comparing the caterpillar abundance, herbivory, and performance on two invasive shrubs in Ohio, Amur honeysuckle (Lonicera maackii) and border privet (Ligustrum obtusifolium), to that of caterpillars on two phylogenetically and ecologically close native counterparts: blackhaw (Viburnum prunifolium) and ash (Fraxinus spp.). Herbivory and caterpillar abundance were far lower on Lo. maackii than on V. prunifolium; however, both metrics were similar between Li. obtusifolium and Fraxinus spp. The probability of survival to pupation trended higher for caterpillars on native plants overall and was significantly higher on Fraxinus spp. than on Li. obtusifolium. Additionally, there was a non-significant, but suggestive, trend toward lower growth rates of caterpillars on the exotic host plants. These results suggest that exotic shrubs are inferior to native plants as hosts for caterpillars and may support depauperate herbivore communities. Consequently, we expect that the continued spread of these exotic plants will erode ecosystem function in eastern North American woodlands.