Abstract: Field experiments were conducted in 30.2m tall empty concrete silos. Threereplications were completed, each on consecutive days, consisting of one heated silo and one silounder ambient conditions. A Mobile Heat Treatment Unit was used to introduce heat into thesilos. When the average temperature in a heated silo reached 50°C, heating was continued onlyfor the next 8h. Ventilated plastic containers with a capacity of 100g of wheat kernels held all lifestages of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) and Tribolium castaneum(Herbst) (Coleoptera: Tenebrionidae). Polyvinyl chloride containers with a capacity of 300g ofwheat held adults of two psocid species: Liposcelis corrodens (Heymons) (Psocoptera:Liposcelididae) and L. decolor (Pearman) which were contained in 35 mm Petri dishes within thegrain. Containers were fastened to a rope suspended from the top of the silo at depths of justunder the top manhole, 10.1, 20.1, and 30.2 meters below the top manhole. There was 100%mortality of adult T. castaneum at the lower three depths but 4% survived near the top manholewhere it was slightly cooler, while >99% survived in the control silos. T. castaneum progenywere produced only near the top manhole in the heat treatments. For R. dominica, adult survivalin the heat treatments averaged 39.3, 6.6, 0, and 1.0% at increasing depths, while survival wasgreater than 95% in the control silos. Progeny of R. dominica was produced at all depths in theheat treatments except where there was no adult survival. There was 100% mortality ofL. corrodens at all depths in the heat treatments but only 92.5% mortality for L. decolor withthose surviving being located at the top manhole level. Wheat kernels had a strong insulatingeffect. Economics of heat treatment are evaluated.