The feasibility of mass marking western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, beetles with fluorescent powder was studied in field cages and with release-recapture. In field cage studies, no significant (P > 0.05) relationship was found between beetles marked with red or green fluorescent powder and beetle mortality. Red marks on beetles were visible with the unaided eye for at least 10 days after marking; however, a binocular microscope was needed to detect green marks on 50% of the individuals after only 4 days. Marking females with flourescent powder did not significantly affect ovarian development. From two releases of red-marked beetles made in the center of a 16 × 40.5-m cornfield, 6.5% of 3,909 and 8.4% of 1,873 adults were recaptured during trapping periods of 10 to 13 days by semiochemical-treated and blank sticky traps placed around the perimeter or within the field. Ovarian development of the marked females recaptured with the traps was not significantly different from that of unmarked beetles caught on the same traps during the same time period.