Feed and Host Genetics Drive Microbiome Diversity with Resultant Consequences for Production Traits in Mass-Reared Black Soldier Fly (Hermetia illucens) Larvae

Simple Summary The development of edible insect farming is crucial for meeting agricultural sustainability goals in the face of growing food demands, ongoing depletion of natural resources, and global climate change. The black soldier fly is considered a promising candidate insect for cultivation, with the larvae of this species being capable of converting agri-waste materials into valuable products that can be used as alternatives to conventional, environmentally detrimental animal feedstuffs, such as processed soy and fish commodities. The biodegradative performance of this species is underscored by the activity of intestinal microorganisms, suggesting that knowledge of larval microbial diversity may be valuable for ensuring sustainability and continual improvement of commercial black soldier fly colonies. In this study, the factors that shape the identity and function of larval gut microbial populations were evaluated. It was determined that both host genetics and diet alter the diversity and metabolic potential of intestinal bacteria, with potential downstream effects on economically important larval rearing traits. Therefore, the findings of this study provide a foundation for expanding and exploiting knowledge of the interactions between black soldier flies and their resident microbial communities for optimisation of insect farming practices. Mass rearing the black soldier fly, Hermetia illucens, for waste bioremediation and valorisation is gaining traction on a global scale. While the health and productivity of this species are underpinned by associations with microbial taxa, little is known about the factors that govern gut microbiome assembly, function, and contributions towards host phenotypic development in actively feeding larvae. In the present study, a 16S rDNA gene sequencing approach applied to a study system incorporating both feed substrate and genetic variation is used to address this knowledge gap. It is determined that the alpha diversity of larval gut bacterial communities is driven primarily by features of the larval feed substrate, including the diversity of exogenous bacterial populations. Microbiome beta diversity, however, demonstrated patterns of differentiation consistent with an influence of diet, larval genetic background, and a potential interaction between these factors. Moreover, evidence for an association between microbiome structure and the rate of larval fat accumulation was uncovered. Taxonomic enrichment analysis and clustering of putative functional gut profiles further suggested that feed-dependent turnover in microbiome communities is most likely to impact larval characteristics. Taken together, these findings indicate that host-microbiome interactions in this species are complex yet relevant to larval trait emergence.