Urban substrates alter the nutritional composition of an emerging model insect, Tenebrio molitor

Although mealworms (Tenebrio molitor) typically consume grains, studies reveal they also consume decaying plant matter, animal waste, and even plastics. The goal of this work was to study mealworms as an emerging model organism to understand how feeding in an urban environment impacts the nutritional composition of insects. We evenly divided 3500 mealworms among each of the following seven substrates designed to model potential food sources in urban versus more natural areas: wheat germ (control); Styrofoam (STY); mixture of soil, grasses, and leaves from urban (UL) or rural lawns (RL); wheat germ with carrot slices (WG + CAR); and organic potting soil in the absence (PS) or presence of Turf Builder (PS + TB). Mealworms were fed for three weeks, after which we measured whole body mass, protein, crude fat, total sugars, glucose, water, and oxidized lipoproteins. No significant differences in nutrient composition were found between mealworms fed soil or lawn substrates. Mealworms fed PS, PS + TB or WG + CAR had lower oxidized lipoproteins compared to the WG diet, likely attributed to antioxidants present in PS and carrots. Mealworms consuming soils or lawns were relatively deficient in proteins, fats, and sugar nutrients compared to WG or WG + CAR, although they maintained higher water content. In contrast, mealworms consuming Styrofoam contained less dietary fat and total sugars than WG or WG + CAR, and less water, but more crude fat, than either soil substrate. These findings demonstrate that mealworms consuming urban-associated substrates (i.e. potting soil, lawns, Styrofoam) are nutritionally deficient compared to those consuming wheat germ with or without carrots.