From Promotion to Inhibition: A Holistic Perspective on the Biological Effects of Polylactic Acid Microplastics on Black Soldier Fly Larva in Food Waste Bioconversion

Food waste (FW) has become a major reservoir of biodegradable microplastics, particularly poly (lactic acid) microplastics (PLA-MPs), posing emerging risks to insect-based bioconversion systems. This study assessed the dose-dependent impacts of PLA-MPs on black soldier fly larvae (BSFL) and uncovered underlying mechanisms using integrated whole-larva transcriptomic, antioxidant enzymatic, gut microbial, and metabolomic analyses. Low PLA-MP exposure (1% w/w) significantly promoted larval performance, increasing body weight by 33% and waste reduction index by 12%. These improvements were linked to activated nutrient-utilization pathways, enhanced antioxidant enzyme activities mitigating mild oxidative stress, and enrichment of beneficial gut microbes, supporting gut homeostasis. In contrast, high PLA-MP exposure (5% w/w) suppressed growth, reducing body weight by 15.3% and survival by 10.86%. These adverse outcomes were driven by excessive oxidative stress and disrupted energy metabolism, which induced detoxification responses. Consistently, the 5% group showed a transition from deterministic to stochastic gut microbial assembly and enrichment of opportunistic pathogens. Overall, this study clarifies the contrasting biological effects of PLA-MPs on BSFL and provides essential insight into evaluating biodegradable microplastics in organic waste treatment systems.