Impact of heavy metals, microplastics, and food pathogens on black soldier fly larvae

The larvae of the Black Soldier Fly (BSF), Hermetia illucens, are efficient decomposers of waste streams thanks to their ability to grow and develop on a wide variety of decaying substrates, even those highly contaminated by various xenobiotics. In particular, certain contaminants could potentially reduce the efficiency of the insect-mediated bioconversion process, but also have an impact on the larvae, thus affecting the quality of the final insect biomass. To investigate this aspect, BSF larvae were reared on a feeding substrate contaminated with different concentrations of lead, PET microparticles, or Staphylococcus aureus, to assess the effects of heavy metals (HMs), microplastics (MPs), or pathogens, respectively, on various larval biological parameters. The three xenobiotics differentially affected insect physiology, indicating the ability of BSF larvae to manage specific contaminants depending on their nature. In particular, HM exposure had a significant impact on the larvae, affecting not only larval growth and survival rate, but also stimulating their immune system. Moreover, a complete elimination of the tested xenobiotics was observed only for food pathogens, confirming the recalcitrant nature of HMs and MPs as a factor that must be carefully taken into consideration, especially when the final insect biomass is used as animal feed ingredient or frass is utilized as fertilizer. This study highlights the complex interactions between BSF larvae and specific environmental contaminants, providing insights into their effects on larval biology and potential implications for bioconversion efficiency. In particular, the ability of BSF larvae to eliminate foodborne pathogens suggests a promising role in waste sanitation, whereas the accumulation of heavy metals in the larvae and/or in the substrate raises concerns about the safety of the resulting insect biomass and frass. These findings emphasize the need for further research to develop entomo-remediation strategies and assess the implications of xenobiotic contamination in large-scale applications.