As global food demand surges, it becomes vital to identify effective methods to mitigate agricultural waste. Recent research has explored the application of black soldier fly larvae as a solution for processing both pig and chicken manure. The study focuses on microbial safety, potential transfer of resistance genes, and risks associated with heavy metals.
The black soldier fly, Hermetia illucens, presents a promising option for waste reduction in livestock farming, yet further investigation into the safety and scalability of these systems is necessary. Concerns regarding bioaccumulation of pathogens, antimicrobial resistance, and heavy metal accumulation in the larvae and their substrates persist.
Research Methodology
A study conducted by researchers from the University of Leeds, in collaboration with the insect farming technology company Entocycle, utilized both semi-commercial and lab-based environments for their experiments.
The semi-commercial facility was employed to rear larvae using pig slurry, while a controlled lab experiment was conducted on chicken manure.
Impact of Insects on Waste Properties
The composition of the larval microbiome was significantly influenced by the type of substrate. Increased levels of Clostridia were observed in larvae raised on slurry and manure. Notably, pathogen levels decreased substantially in larvae from the initial stages of rearing.
Time-related changes in both substrates were evident, but the presence of larvae further reduced levels of E. coli in chicken manure (−2.840 LFC vs −1.168 LFC; p<0.05), implying that substrate-related time alterations might hold greater significance than the influence of larvae themselves.
Potential Risks Associated with Insect Use
The changes in antimicrobial resistance genes varied by substrate and specific genes tested. Increases in tetM were noted in chicken manure after larval processing (9.000 vs 10.370 LFC; p<0.001), as well as for sul2 in chicken manure-reared larvae (3.509 vs −0.985 LFC; p=0.001).
However, in larvae reared on pig slurry, a decrease in tetM levels was observed (−1.578 LFC; p<0.001), with no notable changes for sul2. Heavy metal content in the resultant larvae generally aligned with permissible limits for animal feed and organic fertilizers.
Nonetheless, preliminary evidence suggests possible bioaccumulation of cadmium in slurry-reared larvae (0.18 to 0.70 mg/kg), compared to initial larvae levels (0.25 mg/kg), necessitating further investigation.
This research was supported by an Innovate UK grant, in collaboration with BBSRC as part of the UK government’s initiative to secure the future of the insect farming industry.
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