Toxicity of propolis (bee glue) against the three developmental stages (larvae, pupae, and adults) of the yellow meal worm Tenebrio molitor L. was investigated calorimetrically after dipping the animals for 60 s in different concentrations of propolis dissolved in 55% ethanol. The reduction in the heat production rate due to treatment with different concentrations of propolis displayed similar patterns in the case of larvae and pupae with the mean heat production rate being lowered by more than 90% due to treatment with propolis concentration of greater than or equal to7.5%. In addition the power-time (p-t) curves after treatment became smoother, the extent of smoothing being dependent on the concentration of propolis. Treatment of the adults, however, even with 10% propolis resulted in the reduction of the mean heat production rate by only 28%, with lower concentrations of propolis having no considerable impact.