Effect of yeast supplementation on growth parameters and metabolomics of black soldier fly larvae, Hermetia illucens (L.) (Diptera: Stratiomyidae)

Enhancement of black soldier fly (BSF) larval body weight with nutraceutical metabolites is a crucial step in utilising BSF larvae as food and feed. As BSF larvae are found in natural habitats comprising decaying organic matter and thriving with yeast species, we hypothesis that metabolic interactions between BSF larvae and the yeast present in their gut will have the greatest influence on the nutritional composition and life cycle of the BSF larvae. In the present study, we compared BSF larvae that were fed with Saccharomyces cerevisiae (Sc), a yeast species used for rearing BSF and Candida spp. (Cs), yeast-like fungi that are common in the BSF larval gut environment. The effect of the yeasts on 5^th instar larval body weight was tested, and alteration of metabolic regulation and its impact on related pathways was analysed using liquid chromatography-mass spectrometry (LC-MS) and MetaboAnalyst 5.0 version. The Cs feeding treatment significantly increased larval body weight compared to the Sc treatment. The metabolic pathway analysis demonstrated that the significantly over-accumulated metabolites in the Cs treatment (compared to the Sc treatment) were tyrosine, purine, histidine and vitamin B6 metabolism, while the significantly down-accumulated metabolites in Cs (compared to the Sc treatment) were arginine biosynthesis, phenylalanine, tyrosine and tryptophan biosynthesis, and valine, leucine and isoleucine biosynthesis. In addition, metabolites related to phenylalanine metabolism, D-glutamine and D-glutamate metabolism, and alanine, aspartate, and glutamate metabolism were down-accumulated. However, further study is required on both the BSF and yeast gene expression related to these metabolic pathways in order to better understand yeast-insect metabolite interactions. The overall conclusion of this study is that a supply of yeasts that are adapted to the BSF digestive system contributes to altered metabolic pathways in the BSF larvae and enhances larval body weight, as well as improving nutrient status.