Aerosol insecticides are being used in flour mill pest management programs, but there is limited information on their efficacy on different insect life stages. In this study, we evaluated the efficacy of synergized pyrethrin applied as an aerosol against eggs, larvae, pupae, and adults of the red flour beetle, Tribolium castaneum (Herbst), and the confused flour beetle, Tribolium confusum Jacquelin du Val. Effects of direct and indirect exposure were evaluated by exposing each life stage to the aerosol and then transferring to untreated flour, transferring untreated insects to treated flour, or exposing both the insects and the flour to the aerosol. The aerosol produced >88% mortality of both species and all life stages when insects were directly treated and transferred to either treated or untreated flour. Mortality was significantly reduced when insects were either treated together with flour or untreated insects were transferred to treated flour (indirect exposure to the aerosol). Larvae and adults of both species were more tolerant compared with eggs and pupae. Recovery of moribund adults in the indirect exposure treatments was greater compared with recovery of moribund insects in the direct exposure treatments. Good sanitation before aerosol application could facilitate direct exposure of insects and thus increase aerosol efficacy inside flour mills.