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Simple Summary: The increasing world population generates a huge volume of food waste. The use of black soldier fly larvae in the bioconversion of food waste is a new approach and an interesting example of a sustainable, circular economy approach. In this study, different food waste and residues (ranging from a vegetable to a carnivorous diet) were used as rearing substrates for black soldier fly larvae. The effects of different substrates on larvae development, bioconversion efficiency, and variations in surface temperatures were investigated. The results highlighted how an omnivorous diet provides performances comparable to the high-quality substrate diet (commercial chicken feed) and, therefore, can represent an effective strategy for rearing larvae while reducing food waste. Black soldier fly larvae (BSFL) can utilize food by-products or residues for growth, benefiting farm animal's diets' production sustainability. The experiment aimed to assess the effect of different substrate compositions on larval growth, chemical composition, and substrate temperature. BSFL were allocated to one of the four diets (control, vegetable, carnivorous, and omnivorous) for the entire experiment (8 days). The temperature was measured twice daily using a thermal-imaging camera, and the accumulated degree hours (ADH) was calculated. The results showed that the larvae fed the vegetable diet exhibited a significantly reduced growth performance, with a biomass reduction of 26.3% compared to the control diet; furthermore, vegetable-fed larvae showed a lower dry matter content (−30% compared to the average of other diets) due to lower fat content (−65% compared to average of other diets). The nutritional composition of larvae fed an omnivorous diet was similar to larvae fed a high-quality substrate diet (control diet-chicken feed), indicating that the omnivorous diet could be an ideal solution for rearing BSFL larvae; however, the current European legislation prohibits the use of animal meal. The study also revealed that substrate temperatures did not have a discernible influence on larval growth, further emphasizing the importance of diet in BSFL rearing strategies. [ABSTRACT FROM AUTHOR]

[Display omitted] • Insect rearing is as innovative way to face agri-food by-products management. • Biomass valorisation and creation of new value for feed and agricultural sector. • Building local industrial symbiosis among food and insect producers. • Possibility to adapt insect-based methodological approach for different areas. With a growing population, both food and waste production will increase. There is an urgent need for innovative ways of valorizing waste. The black soldier fly (Hermetia illucens L.) efficiently converts agri-food by-products (BPs) into high-quality materials; its rearing process yields larvae (BSFL) rich in fat and protein for feed purposes, with "frass" acting as organic fertilizer. While the insect rearing sector is expanding, few producers use BPs. Therefore, a case study approach was adopted to evaluate the potential for establishing an Italian BSFL production plant on BPs available on the territory. After contacting more than 115 agri-food companies (maximum 100 km from the BSFL plant), they were classified based on sector, distance, size, and BPs (quantity, seasonality, management). BPs with a low value (fruit and vegetable residues) were treated as waste, associated with costs and low valorization. By merging the available BPs on the territory and following the literature on BSFL nutritional needs' two diets (Scenario BSFL) were created, assessing their suitability comparing them to the current full-scale plant diet (Scenario 0). The exploitation of BPs for BSFL rearing reduced local waste production by 52 % compared to conventional composting (Scenario 0). In addition, integrating BPs into the larval feed formulation increased BSFL production value (+47 times). These results highlight the potential of locally-based insect rearing to valorize BPs and create a network of sustainable actors within the agri-food industry. Further investigations are needed to improve the connection between agri-food and insect industrial activities, expanding this framework to other regions. [ABSTRACT FROM AUTHOR]