Cry3Bb protein expression tests were evaluated as a method to identify Diabrotica virgifera (Coleoptera: Chrysomelidae; western corn rootworm) adults that had recently fed on Cry3Bb protein-expressing corn plant tissues (Monsanto event MON863). To establish background information about D. virgifera feeding behavior, adults were offered corn foliage, corn pollen, corn silks or soybean foliage (all plant tissues D. virgifera consume in the field). The most sustained feeding response was observed among beetles fed corn silks. The interval between consumption and first appearance of a food item in feces (gut passage time) ranged from 102.7 ± 11 min (mean ±SEM) for soybean foliage to 56.7 ± 2.9 min for corn silks. In a laboratory feeding study using Cry3Bb protein expression tests to detect Cry3Bb protein in the guts of beetles that had been fed on MON863 corn silks, the proportion of Cry3Bb-positive insects was inversely proportional to the time since last feeding on MON863 tissue. Cry3Bb protein was detectable in D. virgifera adults up to 16 hours after they had last eaten MON863 corn silks. No feeding deterrence or acute mortality among the MON863-fed insects was observed. Among insects collected in the field, a high proportion of adult D. virgifera from in and around MON863 field plots and an adjacent soybean field tested positive for Cry3Bb protein. Based on the distance between the MON863 sources and where insects testing positive for Cry3Bb protein were collected, we estimate that 85.3% of male or female D. virgifera move no faster than 6.9 m/d through R2-R3 stage corn. For D. virgifera that left corn and were captured in the adjacent soybean field, we estimate that 86.4% of males and 93.1% of females move no faster than 9.1 m/d through soybean. Detection of transgenic plant tissues in the bodies of mobile insect herbivores represents a novel application of biotechnology to the study of insect movement.