A solinvivirus induces cellular antiviral response and reduces the lifespan of adult Hermetia illucens (black soldier flies)

Viral pathogens pose an emerging threat to the sustainability of insect mass-rearing systems, yet remain understudied in key species like the black soldier fly (BSF, Hermetia illucens). Although multiple viral sequences have been reported in BSF, their role in disease has not been established until now. Here, we provide the first in vivo characterisation of Hermetia illucens solinvivirus (HiSvV), confirming its role as a viral entomopathogen of BSF. Metatranscriptomic analysis of a diseased colony revealed a high viral load attributable to HiSvV. We successfully isolated the virus and developed injection- and oral-based infection assays to investigate replication, tissue tropism, transmission and risk of mortality. HiSvV replicated in inoculated adults, induced premature mortality in flies, and was transmitted both horizontally and vertically. Infected flies also mounted a broad antiviral response, supporting active pathogenesis. These findings establish HiSvV as the first confirmed viral pathogen of BSF and underscore the urgent need for viral surveillance and experimental tools to safeguard industrial insect rearing.