Understanding Pathogen Risks in Black Soldier Fly Production: An Integrated Review

As global interest in insects as sustainable sources of protein and fat continues to grow, the black soldier fly has emerged as one of the most promising species for large-scale production. Its larvae efficiently convert low-grade organic waste into high-value nutrients, making it a cornerstone of circular feed systems. Yet, with the rapid expansion of industrial BSF farming, concerns about potential disease outbreaks inevitably come to the forefront. Remarkably, despite the species’ commercial rise, no major pathogen-driven collapse has been documented in BSF farms to date. This stands in stark contrast to other mass-reared insects, such as mealworms, which have experienced notable disease events.

Understanding why BSF appears so resilient—and which threats may pose genuine risks—is critical for safeguarding future production. A review of existing research on entomopathogens affecting Diptera (the insect order to which BSF belong) sheds light on the immune defences of BSF, potential pathogen groups, and the management strategies needed to maintain a robust farming system.

The Natural Defenses of the Black Soldier Fly

Like all insects, BSF rely exclusively on innate immunity. Yet this innate system is sophisticated, relying on specialized blood cells, rapid production of antimicrobial peptides, and processes such as melanisation and phagocytosis to neutralize invaders. Studies on BSF are still limited, but early findings suggest that larvae possess a broad antimicrobial repertoire and can even reduce harmful pathogens such as Salmonella in their substrate. This capacity may partially explain why natural disease outbreaks appear rare.

Research on related dipteran species, particularly the fruit fly and housefly, provides additional clues. These insects produce a wide array of antimicrobial peptides tailored to combat bacteria and fungi. BSF share similar systems, although their exact immune mechanisms remain an important topic for future investigation.

Potential Pathogens: Fungi, Viruses, Protozoa, and Bacteria

Fungi

Entomopathogenic fungi are widespread in nature and often target adult flies or larvae of dipteran families. Yet intriguingly, no natural fungal infections have ever been reported in BSF. Whether this is due to true resistance or simply a lack of sampling remains unclear. Some well-known fungal biocontrol agents could theoretically pose a risk if introduced into a BSF facility, especially through contaminated feed or nearby agricultural activities.

Viruses

Viruses represent a major threat in insect industries. Some reduce fecundity or cause lethal infections in houseflies or tsetse flies. For BSF, however, no viruses have yet been identified. The greater concern lies with “covert infections”—viruses that remain latent until triggered by stress. As production scales up, routine screening of both wild BSF populations and production colonies will become essential.

Protozoa

Protozoan parasites, including microsporidia and gregarines, can cause chronic and sometimes devastating infections in other farmed insects. While none have been documented in BSF, their presence in related Diptera means the potential for transmission cannot be ruled out, particularly through contaminated substrate.

Bacteria

Bacteria represent both a challenge and an advantage for BSF. On one hand, opportunistic pathogens such as Serratia, Pseudomonas, and Bacillus species are commonly found in the environment and could infect stressed larvae. On the other hand, BSF larvae are known to suppress harmful bacteria in their substrate, enhancing the safety of the resulting biomass. The relationship between substrate composition, larval health, and microbial load is therefore a crucial research area.

Detecting Disease: Tools and Techniques

Diagnosing pathogens in BSF requires a combination of classical and modern biological techniques. Fungal infections can be identified via microscopy and morphological traits, while viral detection relies heavily on PCR and sequencing. Protozoans typically require dissection and microscopic inspection of gut contents. Bacterial pathogens are isolated from haemolymph or tissues and identified using either culture-based diagnostics or molecular methods such as 16S rDNA sequencing or MALDI-TOF.

Farmers play an important frontline role in surveillance. Early intervention requires timely collection of fresh samples, recognition of abnormal behaviour or morphology, and close cooperation with specialized diagnostic laboratories.

Managing Pathogen Risks in Production Systems

BSF farms can be viewed as biological fortresses: their success depends on preventing pathogens from entering and limiting their spread if they do.

Two major pathways threaten facility biosecurity:

1. Contaminated feed.
   Organic waste streams may contain insect pests, fungal spores, bacteria, or residues of biocontrol agents. Heat treatment, milling, or radiation can reduce risks, though energy costs may be significant. Visual inspection alone is insufficient.
2. External insects.
   Wild Diptera, including escaped BSF adults, can function as vectors. Closed facilities with mesh barriers, controlled airflow, and restricted entry points drastically reduce these risks. Quarantining new genetic lines and using SPF broodstock are additional safeguards.

Inside the facility, pathogen spread can occur through cannibalism, airborne spores, contaminated surfaces, or water supplies. Effective disease management therefore involves:

• careful control of humidity and temperature,
• batch-wise rearing with sanitation between cycles,
• rigorous cleaning with detergents and UV treatment,
• modular facility design to isolate production zones,
• insect traps to prevent movement of inadvertent vectors.

Well-designed closed facilities offer the strongest protection, although poorly engineered ones can inadvertently create microclimates ideal for pathogen growth. In some situations, simpler semi-open systems may be more resilient.

Looking Ahead: Research and Industry Priorities

Despite the current absence of major disease issues, the authors emphasize that pathogens will inevitably emerge as the BSF industry scales up—a pattern seen in every other domesticated species. Initiative-taking investment in research, monitoring, and facility design is therefore essential.

Future studies should focus on:

• discovering natural pathogens in wild BSF populations,
• understanding microbial dynamics in substrates,
• assessing spillover risks from agricultural biocontrol agents,
• exploring the use of beneficial microbes or probiotics,
• developing standardized diagnostic and monitoring systems,
• applying metagenomics for rapid pathogen identification.

Collaboration between researchers, producers, veterinarians, and diagnostic laboratories will be vital in building a sustainable, disease-resilient BSF production sector.