Growing demands for bioenergy are driving substantial land cover conversion worldwide. Ecological assessment of this landscape transformation recognizes the tremendous potential for altering regional economies and ecological sustainability. A key area of uncertainty is consequences for pathogen and vector dynamics. Perennial biofuel crops may provide long-term refugia for pests and pathogens and potentially amplify their numbers.When biofuel crops are grown in regions with closely related native species or food crops, such as switchgrass (Panicum virgatum) grown in the Midwestern US, pathogen spillover among landscape compartments could be significant. To develop models of bioenergy crop impact on regional pathogen dynamics, we are quantifying key interactions among different land covers and a group of generalist plant viruses--Barley and cereal yellow dwarf viruses (B/CYDVs)--and their aphid vectors, which are an emerging model system in disease ecology. We conducted a landscape-scale analysis of vector and virus incidence in potential biofuel crops in different landscape contexts in the Great Lakes region. We measured virus incidence in switchgrass and aphid pressure in fields of maize, switchgrass, and prairie across a 300-km transect in Michigan. We evaluated relationships among virus and vector pressure, local community structure, and landscape context determined from aerial photography. 

Results/Conclusions

We found high levels of virus infection in some switchgrass plantings—up to 30% incidence of B/CYDV in sampled fields, indicating the potential for biofuel crops to act as virus reservoirs. Virus incidence in switchgrass was correlated with vector pressure across the landscape, underscoring the key role of vector ecology in determining infection patterns. Landscape diversity notably influenced pathogen and vector pressure: early summer vector pressure strongly increased as landscape structure became simpler. Particular land cover types also affected early summer aphids: fields surrounded by larger areas of row crops had fewer aphids, while fields surrounded by greater areas of forest had more aphids. Areas with higher aphid and virus pressure could be a source of vector and pathogen spillover into other vegetation types, particularly if biofuel crops are planted with virus-susceptible varieties. This is of particular concern given previous work demonstrating that switchgrass varieties selected for biofuel-valuable traits are more susceptible to B/CYDV infection than wild-type switchgrass varieties. The potential for changes to biotic interactions as result of biofuel-driven landscape modifications are considerable, and without an understanding of pathogen and vector interactions, unforeseen consequences, such as pathogen spillover into remnant vegetation, could result.