We evaluated the suitability of forty-four commodities (i.e., cereal flours and meals, non-flour, cereal commodities, legumes and various commodities of vegetative and animal origin) as oviposition and feeding substrates for the yellow mealworm, Tenebrio molitor. Τen T. molitor adults were introduced in plastic vials containing 30 g of each commodity. At the end of the 1 week period, all adults were removed, and mortality was determined; then the vials were further incubated for additional 9 weeks. After this time, the vials were opened, and the larvae of each vial were separated from the feeding substrate, counted and weighed as a group. The efficiency of ingested food conversion was calculated for each substrate. Finally, proximate composition was calculated to determine the nutrient components of the feeding substrates tested and the T. molitor larvae that fed on various selected substrates. In general, adult reproduction was clearly favoured by most amylaceous substrates tested, which was in contrast to the tested legumes on which fewer offspring were produced. Similar effects were observed for larval development. Feeding on selected substrates exerted an impact on the nutrient composition of T. molitor larvae, with a high protein content of the substrate usually resulting in a high protein content of the larvae.