In Illinois and Indiana, the western corn rootworm, Diabrotica virgifera virgifera LeConte, circumvents crop rotation as a control measure by ovipositing in soybean (Glycine max L. Merr.) fields and in other crops in rotation with corn (Zea mays L.). A means of distinguishing between rotation-resistant and wild-type behavioral phenotypes is the first step in determining the genetic basis of rotation resistance. The time between release into and departure from a bioassay arena was used as a measure of beetle activity to distinguish between behavioral phenotypes. Results from these assays indicate that D. v. virgifera females from regions where crop rotation is no longer effective are more active than females from regions where rotation remains effective. The geographic source of the beetle population was a main significant effect in trials done in both 2004 and 2005. Behavioral differences were more easily observed in a cornfield rather than in the laboratory. Results were consistent with the hypothesis that a loss of fidelity to corn rather than any particular attractant is the cause of rotation resistance. Behavioral differences between populations of beetles in similar environments suggest that there is a genetic difference between rotation-resistant and wild-type D. v. virgifera, although no specific gene or genes have yet been identified.