Impact of agro-industrial by-products on nutritional value and microbiota composition of black soldier fly larvae

In this study, interrelations between agro-industrial by-products, black soldier fly larvae (BSFL) rearing, and associated microbiota were investigated. Carrot pomace, brewer's yeast, spent grains, and rape press cake were used as feed substrates, varying in their chemical composition, nutritional value, and microbial load and diversity. Overall, the data did not reveal a consistent or direct relationship between substrate chemical composition and nutrient profile of the BSFL, suggesting that larval development may be influenced more by complex substrate-microbe-larva interactions than by substrate chemistry alone. Using brewer's yeast, the highest average larval biomass (184.3 mg/larva) and crude protein content (61.1%), as well as high crude fat content (24.3%), were obtained. Fatty acid analyses of BSFL revealed diverse patterns with high saturated (stearic acid, palmitic acid, myristic acid, lauric acid) or unsaturated (oleic acid, linoleic acid) fatty acid contents in BSFL reared on carrot pomace and brewer's yeast, or on rape press cake, respectively. The composition of the substrate, either nutrient (dietary fibre) or microbiota-wise, markedly influenced the BSFL microbiota. Several species of lactic acid bacteria and <i>bacilli</i> were found to be potentially transferred from the substrate to the BSFL microbiota. On the other hand, several taxa of the genera <i>Actinomyces</i>, <i>Morganella</i>, <i>Klebsiella</i>, and <i>Enterococcus</i> were identified to belong to the core microbiota of BSFL, independent of the substrate. The study advances our understanding of how substrate selection affects the performance, nutrition, and microbiota of BSFL, providing insight into the possibilities for sustainable waste management and protein production systems.