An actograph was used to determine diel locomotor periodicity and influence of constant and changing temperatures on adult western corn rootworm (Diabrotica virgiferaLeConte) locomotor activity in the laboratory. Diel periodic fluctuations in activity occurred with reduced activity from 9 a.m. to 5 p.m. and a high level of activity from 5 p.m. to 8 a.m. Maximum activity for males and females occurred at 23°–25° and 25°–27°C, respectively, with negligible activity for both sexes at 10° and 40°C. Males were generally more active than females, especially in the maximum activity temperature range. Female activity exceeded male activity at high temperature ranges. Decreasing temperature conditions increased activity levels over constant-temperature comparisons at low temperatures for both male and female beetles.