The Influence of Native Plants on Arthropod Population Dynamics: Can Natives Enhance Conservation Biological Control?

Graduate Research Assistant: Ellery Vodraska (MS Entomology, University of Maryland)

Collaborators: Paula Shrewsbury, Mike Raupp, Kimberley Shropshire

Research has shown that predators and parasitoids of phytophagous arthropods suppress pest populations more often and more successfully in the presence of a diversity of alternative prey species. This relationship forms the central tenet of conservation biological control and has stimulated efforts to attract sustainable populations of alternative prey to simplified anthropogenic ecosystems. This goal may be more easily achieved if native plants dominate the first trophic level of these ecosystems. Plant-insect interaction theory predicts that specialist herbivores (an estimated 90% of phytophagous insect species) will be unable to grow and reproduce on alien plant species with which they have no evolutionary history. If this is so, the overuse of alien ornamentals in millions of hectares of suburbia may have reduced the ability of native phytophagous insects to support the diverse population of natural enemies needed to control outbreaks of pest species. Our project tests the hypothesis that native insect herbivores, and thus their natural enemies, can be sustained in urban ornamental gardens when alien plants are replaced with native hosts of these herbivores. We predict that, once established, this complex of predators and parasitoids will prevent eruptive pest outbreaks without the use of pesticides. We are using replicated gardens to compare the density and diversity of phytophagous insects and their natural enemies, as well as the population dynamics of six common urban pests in plots comprised entirely of native or alien ornamental plants. We are also comparing the length of time both treatments remain below the aesthetic injury level of 10% foliage damage. The results of this project may provide practitioners of conservation biological control with a new, effective, and environmentally friendly tool for managing pests in ornamental gardens throughout North America. Equally important, this study will establish baseline data on the importance of native plants in maintaining some semblance of biodiversity in the growing suburban ecosystem.