Survival and bacterial load of black soldier flies pupating in different substrates

Biological conversion of waste into ingredients of animal feeds and organic fertilizers using the larvae of black soldier fly, Hermetia illucens, is a rapidly growing environmentally sustainable industry. However, pathogenic bacteria associated with decaying waste may create safety problems, potentially undermining this technology. Adult flies escaping from rearing facilities may contribute to spreading such pathogens. We quantified bacterial communities associated with the adult black soldier flies that pupated either in their original larval substrate (rotten potato) or in sterile sawdust. We also tested if inoculating the larval substrate with methicillin-resistant Staphylococcus aureus (MRSA) will result in the adults carrying this bacterium. Black soldier fly adults that pupated in sawdust had better survivorship and faster development than the ones that pupated in the potato. Total bacterial counts were greater in flies from the potato substrate, but there was no difference in non-lactose fermenting bacteria. Abundance of Staphylococcus spp. remained low regardless of MRSA inoculation. The dominant taxa found were Gammaproteobacteria, Bacillus, Corynibacterium, Klebsiella, and Escherichia. While the tested adult flies did not transmit MRSA from their pupation substrate, they still carried a diverse array of bacteria, including a common foodborne pathogen Bacillus cereus. This poses a potential risk in large-scale waste management.