We investigated the impact of different fluorescent marking powders on both survivorship and daily body condition, measured as mass/volume ratio, using adult mountain pine beetles, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae), in a laboratory study. Initial condition of the marked beetle groups did not differ from that of an unmarked group. However, beetles in better initial condition survived longer, thus validating our condition index. The condition but not the survivorship of mountain pine beetles was affected by the marking treatment. Overall, the condition of beetles declined over time. The condition of marked beetles decreased at a higher rate than that of unmarked beetles while alive but at a lower rate after death. This pattern of decreasing condition suggests that marked beetles lost water faster than unmarked beetles while alive, so unmarked beetles had more water to lose after death. Because reduced condition may affect optimal dispersal behaviour, we suggest that these effects be routinely examined and minimized in mark-recapture studies.