Black Soldier Fly Adults as Potential Vectors of Methicillin-Resistant Staphylococcus aureus and Other Pathogenic Bacteria

There is a growing global need for sustainable waste management solutions, and alternative protein sources for livestock. This has led to the widespread adoption of black soldier fly larvae (BSFL, Hermetia illucens) in organic waste recycling, including valorizing cull potatoes. BSFL has complex interactions with the microorganisms that inhabit the same decaying substrates, suppressing many species but promoting other species. This research explored the potential for BSFL and BSF adults to harbor and transmit pathogenic bacteria, including Methicillin-resistant Staphylococcus aureus (MRSA), which pose a significant threat to public health. Findings indicated that MRSA levels were initially increased in the presence of larvae. However, that was followed by a significant decline in MRSA colony counts in the same substrates. This suggests that the larvae have a delayed but significant antimicrobial effect. A common antibiotic ampicillin suppressed total bacterial abundance but lost its efficacy over time. There was no significant reduction in total bacteria observed when ampicillin was combined with BSFL, possibly because the larvae encouraged MRSA proliferation in the early stages. Additionally, larvae reared on substrates treated with ampicillin showed increased growth, likely due to a reduction in bacterial competitors. Dysgonomonas was the most abundant bacterial genus, followed by Frischella, Klebsiella, Providencia, Propionibacterium, and Lactococcus. Fungal communities were dominated by Galactomyces and Candida. To determine whether BSF adults could serve as a vector for MRSA, larvae were reared in both inoculated and control decaying potato substrates and allowed to pupate either in their original medium or in sterile sawdust. Our findings confirmed that sterilized sawdust was a more effective pupation substrate for BSFL than decaying potatoes, resulting in better survival and faster development. This was likely due to improved aeration and lower microbial load, as the potato substrate supported dense bacterial communities—particularly Gammaproteobacteria—that may have hindered larval health. BSF adults emerging from potatoes carried a higher bacterial load but lower bacterial diversity, suggesting that substrate plays a major role in shaping the microbiome of emerging flies. Although MRSA did not persist in the system, the presence of other bacteria, such as Acinetobacter sp., highlights the need for continued biosafety assessments in BSFL-based waste conversion systems. In summary, this research contributes to a deeper understanding of microbial dynamics within insect-based recycling systems and helps clarify the biosafety implications of using BSFL in sustainable agriculture. The findings also highlight that BSF adults, while unlikely to transmit pathogens like MRSA, can still acquire and carry bacteria from their pupation substrates, which poses a potential risk in large-scale waste management. While the larvae offer promising tools for circular waste management, their role in pathogen suppression and transmission must be carefully managed to protect animal, environmental, and public health.