"Some [prairie remnants] are shaped so that no portion is more than a few meters away from the agricultural edge. Such reserves may have little or no area free from the negative effects of edges with agriculture," say Mark McKone of Carleton College in Northfield, Minnesota, and his co-authors in the October issue of Conservation Biology.
Before European settlement, tallgrass prairie covered more than 167 million acres of central North America. Most of the prairie has been converted to corn and other crops, leaving only scattered remnants.
McKone and his colleagues have observed large numbers of a corn rootworm beetle (Diabrotica barberi) near corn edges in prairie remnants in southeastern Minnesota. The larval stage of this beetle is one of the most damaging corn pests and in August, the adults begin moving from corn fields into prairies to feed on pollen and other parts of native flowers. The beetles seem to favor sunflowers and other yellow composite flowers.
The researchers studied corn rootworm beetles in McKnight Prairie, which is in southeastern Minnesota. The 33-acre prairie is long and narrow (about 560 feet across), and is completely surrounded by agriculture. The northern edge was planted with corn during the study, and the southern edge borders a conifer plantation. The reseachers determined the number of beetles at various points across the width of the prairie, and compared sunflower damage at two study sites: near the corn edge and near the conifer edge. These sites were about 130 and 460 feet away from the corn edge, respectively.