Microplastics impair black soldier fly bioconversion of pigeon manure: Physiological and transcriptomic insights

Abstract

The black soldier flies (BSFs) are widely used for efficient conversion of livestock and poultry manure, but the impacts of microplastics (MPS) present in the manure on this process remain unclear. This study investigated the effects of 0.2 % (w/w) PVC microplastics (200 nm) on the bioconversion efficiency of manure by BSFs over a two-week larval development period, incorporating transcriptomic analysis to examine their impacts on larval growth, development, and metabolic processes. Results showed that MPS exposure altered manure physicochemical properties, making it wetter and less palatable, which reduced nitrogen transformation and inhibited larval growth by 11.05 % in body weight and 4.42 % in length. Meanwhile, oxidative stress was significantly elevated, with SOD activity increasing by 106 %, leading to a 26 % increase in early pupation. Transcriptomic analysis revealed that MPS accumulated in the BSF intestine disrupted glutamine metabolism, triggered inflammatory responses, and elevated reactive oxygen species production. Intestinal damage such as villus shedding induced the upregulation of serine endopeptidases. To compensate for impaired digestion, key genes involved in gluconeogenesis were significantly upregulated, including protein kinase A (2.39-fold), L-lactate dehydrogenase (1.72-fold), and pyruvate kinase (2.05-fold), helping to maintain energy homeostasis. Furthermore, nitrogen metabolism pathways showed enhanced expression of glutamate-related genes, facilitating the transition to the prepupal stage. These molecular and physiological responses represent an adaptive mechanism to environmental stress but ultimately resulted in compromised bioconversion efficiency. Therefore, removing MPS from manure is crucial for optimizing BSF-based bioconversion and promoting sustainable waste treatment.