Injury to rotated corn in parts of Illinois and Indiana has been attributed to populations of Diabrotica virgifera virgifera LeConte considered resistant to a corn-soybean rotation. Unlike wild-type that have a high fidelity for corn as an oviposition site, rotation-resistant beetles oviposit in soybeans. We used a side-arm olfactometer to test if putative rotation-resistant and wild-type adults responded differently to soybeans and if corn phenology influenced the relative attraction of adult beetles to soybean versus corn. Beetles from Nebraska where injury to rotated corn has not been reported were defined as wild-type, and beetles from Illinois where injury to rotated corn is common represented rotation-resistant populations. More beetles found olfactometer chambers with soybeans than empty control chambers, but there was no difference in response between these two populations. Numbers of beetles entering chambers with soybean varied in the presence of corn at anthesis (‘young’ corn) versus corn past anthesis (‘old’ corn). Replacing young with old corn doubled the percentage of beetles that did not select corn. Thus, as corn aged adult visitation to soybeans increased with decreasing attractiveness and arrestiveness of corn. We suggest this mechanism can explain injury to rotated corn, when linked to corn planted early and synchronously within a landscape limited to corn and soybean. Given this mechanism, a parsimonious explanation based on behavioral plasticity of the wild type should be given due consideration along with the model in current D. v. virgifera literature that rotation-resistance (i.e. oviposition in soybeans) is due to a genetic change.
Species 1: Coleoptera Chrysomelidae Diabrotica virgifera (western corn rootworm)
Keywords: resistance, rotation
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