Abstract Rollstands (Simons) in three Canadian flour mills were internally sampled and the number of adult and pupae Tribolium spp. present were counted. Middling rollstands had higher infestations than the break rollstands. The number of adult beetles inside the rollstands was compared to beetle activity seen outside the rollstands, which was assessed by counting the number of tracks in front of the rollstands and the number of beetles caught in monitoring traps placed at the foot of each rollstand. Few beetles were caught in traps and they were not correlated with beetle populations inside the rollstands. The tracks showed some correlation with beetles found in the lower sections of the rollstand ( r 2 = 0.20–0.41). The number of adults inside the rollstands was highly correlated with the number of pupae present, indicating long-term infestation. Adult beetles in the rollstands of one mill were analysed to either Tribolium confusum or Tribolium castaneum . Both species were present, but they were spatially segregated.