From waste to resource: agri-food by-products as substrates for Tenebrio molitor rearing

Steady population growth and the increasing global demand for protein require the identification of sustainable alternative sources. Insect farming is widely recognized as a promising solution, particularly when integrated into a circular economy framework. Among major agrobusiness, tomato processing and brewery production generate by-products accounting for approx. 10–30% of the total raw material processed, which contain valuable nutritional components that make them attractive substrates for insect rearing. This study evaluated the suitability of two byproducts as feed source for the yellow mealwormTenebrio molitor L. (Coleoptera, Tenebrionidae). Experiments were conducted separately on two genetically distinct yellow mealworm populations, originating from Milan and Turin. Dried tomato peels and brewer’s spent grain were mixed with wheat bran (1:1, v/v) as growth substrates and were provided along with wheat bran as control treatment. Development time, survival, larval biomass, individual weight and individual length were assessed. For the Milan population, no significant differences were observed between diets in terms of survival (≈95%), total larval biomass, or development time (34 days to first pupation). However, larvae reared on the tomato peel mixture showed a significantly higher mean individual weight and length (0.144 ± 0.004 g; 27.01 ± 0.23 mm) compared to the control (0.096 ± 0.003 g; 22.88 ± 0.28 mm). For the Turin population no significant differences were observed between diets in terms of survival (≈89%), and total larval biomass. Differences were found in development time between brewer’s (118 days) and control diet (50 days). Larvae reared on brewery’s mixture showed a significantly lesser mean individual weight and length (0.075 ± 0.002 g; 19.41 ± 0.22 mm) compared to the control (0.085 ± 0.002 g; 21.48 ± 0.19 mm). Overall, these findings support the potential of tomato peels and brewer’s spent grain as sustainable substrates for yellow mealworm mass rearing. Nevertheless, deformities observed at late larval and pupal stages with tomato peels highlight the need for further investigations on adult reproductive performance and on the possible presence of pesticide residues or anti-nutritional factors, emphasizing the importance of careful selection and quality control of by-products as insect feeding. Acknowledgement: Work funded by PRIN 2022 Project InProFarm (Insect Probiotic-assisted Farming: a promising tool to enhance edible insect health and performances), grant number 2022L4NJMK — Next Generation EU, Mission 4, Component 2.