An edge effect caused by adult corn-rootworm beetles on sunflowers in tallgrass prairie remnants

The once-extensive tallgrass prairie community of North America has been reduced to small remnants, many of which are surrounded by intensive corn (Zea mays) agriculture. We investigated adult corn-rootworm beetles (Cbrysomelidae: Diabrotica spp.), important pests of corn, on sunflowers (Asteraceae: Helianthus spp.) in prairie remnants In southeast Minnesota. Large numbers of beetles invaded the prairie from surrounding cornfields in late summer. D. barberi and D. virgifera were captured on sticky traps in all locations in the prairie, but abundance was much greater near the edge adjacent to corn. We observed D. barberi (but not D. virgifera) feeding extensively on sunflower pollen and occasionally on other flower parts, such as petals. Sunflowers located nearer cornfields sustained more floral damage than those farther from corn. To determine the effect of beetle damage on seed set, we enclosed sunflower heads in bags with either zero, two, or four D. barberi adults. Seed set was reduced in heads enclosed with D. barberi. Thus, this agricultural pest may interfere with the successful reproduction of sunflowers and possibly other prairie composites that flower in late summer. Given the small size of most prairie remnants and the abundance of this flower feeding beetle in landscapes dominated by corn agriculture, D. barberi may affect the sustainability of prairie plant populations.