Rearing of the black soldier fly, Hermetia illucens, in mass production systems is increasing. Its use as both a bio-converter of organic waste and as feed for other livestock has transformed it into one of the most produced insects in the world. As a result, new research is needed to evaluate the risk of insect diseases affecting it and thus productivity. While some studies have focused on the larval stage of the flies, to date, few have assessed risks to the adult stage, vital to the production system. In this study, the susceptibility of adult black soldier flies to the entomopathogenic fungus, Beauveria bassiana KVL 03-122 was evaluated in laboratory experiments by quantifying mortality, egg-laying capacity, and sporulation when the flies were subjected to two concentrations of the fungus. The findings showed that adult flies are susceptible to the biocontrol agent B. bassiana, with high mortality and low egg count in the high dose treatment. Our results confirmed that adult black soldier flies appear susceptible to a fungal pathogen and we discussed the findings in relation to consequences for production.