We used two types of laboratory apparatus to test whether rotation-resistant and wild-type Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) responded differently to corn phenology. 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. A two-chamber emigration arena assayed propensity of both populations to leave corn during and after anthesis. A side-arm olfactometer tested whether the relative attraction of beetles to soybean versus corn was influenced by corn phenology. Beetle origin did not influence departure from corn of varying phenology; both emigrated significantly less from young (shedding pollen) than old (no pollen) corn. Significantly more beetles entered olfactometer chambers with soybean than empty control chambers, but there was no difference in response between the two populations. Numbers of beetles entering chambers with soybean varied with the addition of young versus old corn. Replacing young with old corn approximately doubled the percentage of beetles not selecting corn. As corn aged, adult visitation of soybean increased significantly. We suggest this mechanism is sufficient to explain injury to rotated corn, when linked to a corn crop planted early and synchronously within a landscape limited to corn and soybean. This explanation based on preexisting behavioral plasticity should be given due consideration along with conceptual models of D. v. virgifera rotation resistance that imply genetic change.
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