Larval density drives thermogenesis and affects microbiota and substrate properties in black soldier fly trials

Industrial insect farming has potential for converting low-value organic waste into nutrient-rich insect biomass, producing valuable by-products like organic fertilizers. However, a better understanding of density-related thermogenesis and microbial dynamics is needed to enhance standardization and bridge gaps between laboratory and industry needs. This lab-scale study focuses on the black soldier fly (Hermetia illucens), which exhibits thermogenesis that intensifies with larval population size and its natural crowding behavior. Using high-resolution temperature monitoring and biomolecular methods, we found that doubling larval density (0, 1.25, 2.5, and 5 larvae/cm²) increased temperatures by 0.6°C-2.4°C, depending on the treatment. Adding potassium sorbate altered microbial profiles, increasing Enterobacter and decreasing Providencia, while promoting lactic acid bacteria. Density also impacted pH, water content, dry matter, volatile solids, and ash in the substrate. Our findings provide essential insights into managing microbial and thermal dynamics, offering valuable information for optimizing and standardizing conditions in rearing trials.