Microbiome enrichment from a wild relative improves Black Soldier Fly larval survival, pathogen suppression and growth

Captive rearing can disrupt animal microbiomes, reducing diversity and impairing host performance. For the larvae of Black Soldier Flies (Hermetia illucens; BSFL), a key species in waste bioconversion, microbiome engineering offers a strategy to enhance growth and disease resistance. We tested whether enriching the BSFL microbiome with microbes from a wild relative, Exaireta spinigera, improves larval performance. Axenic BSFL neonates were inoculated with (1) a captive BSFL microbiome, (2) an E. spinigera microbiome, (3) a mixed inoculum of the two, (4) an environmental, diet derived microbiome, or (5) remained axenic. After two weeks, larvae receiving E. spinigera microbes (alone or mixed) exhibited significantly higher growth and survival compared to those inoculated with the captive microbiome. Full-length 16S rRNA gene sequencing revealed successful establishment of diverse taxa from E. spinigera, including Dysgonomonas, Wohlfahrtiimonas, and Scrofimicrobium, some showing strong association with either the larval gut or frass. Notably, enrichment with the E. spinigera microbiome suppressed a pathogenic Pseudomonas aeruginosa strain that dominated the captive microbiome and reduced larval survival in mono-inoculation trials. These findings demonstrate that microbiome enrichment from wild relatives can enhance BSFL health and resilience, supporting a top-down approach to probiotic development for industrial insect rearing. ImportanceBlack Soldier Fly (Hermetia illucens) larvae are increasingly farmed to convert organic waste into valuable products like animal feed and fertilizer. Microbiome composition influences larval health and growth, but captive rearing may restrict or alter functional microbial diversity. Our study shows that enriching the microbiome of captive Black Soldier Flies with microbial diversity of a wild relative species (Exaireta spinigera) improves larval growth while suppressing a pathogenic bacterium. This work demonstrates, for the first time, the potential for utilizing the diversity of microorganisms associated with the over 3000 global species of soldier flies as a source of beneficial probiotics supporting industrial Black Soldier Fly rearing.