A sublethal concentration (2.5%) of tricalcium phosphate, a known insect population suppressant, was used to investigate the effect of this salt on the energy budget of the khapra beetle,Trogoderma granariumEverts. Larvae fed tricalcium phosphate had a longer developmental period and one extra instar; they ingested more food and had a lower mean assimilation efficiency.T. granariumis relatively resistant to tricalcium phosphate and concentrations only in excess of 2.5% will cause any appreciable population suppression. The higher mortality and longer development time of populations treated with tricalcium phosphate were compensated for by a higher production of eggs. Greater numbers of progeny and living longer may even increase consumption. Energy budgets of other stored-product insects were compared with that ofT. granarium.