Death-driven exposure: Necrotrophic transfer of polylactic acid and polystyrene microplastics alters biochemical architecture in the saprophagous insect Chrysomya megacephala

Microplastic exposure (MPs) represents an emerging threat to terrestrial ecotoxicology, particularly within detritivorous ecosystems. In this study, we investigated transstadial bioaccumulation and the biochemical effects of necrotrophic exposure to polystyrene (PS-MPs) and polylactic acid microplastics (PLA-MPs) in Chrysomya megacephala. Mice contaminated with varying concentrations of the polymers were used as larval decomposition substrates. To confirm the prior internalization of MPs, third-instar larvae (L3) were analyzed, revealing significant particle accumulation. We assessed MP retention and biochemical alterations in key physiological systems following adult emergence. The presence of MPs in newly emerged adults, at significantly lower concentrations than those observed in larvae, confirmed transstadial bioaccumulation and indicated partial retention during metamorphosis. Bioaccumulation was more pronounced at higher exposure concentrations. PS-MPs induced functional disorganization, characterized by increased reactive oxygen species (ROS), lipid peroxidation, proteolytic activity, and neuroendocrine dysfunctions. In contrast, PLA-MPs elicited more coordinated biochemical responses, with emphasis on antioxidant activation. Correlation network and functional trade-off analyses revealed distinct patterns of physiological reorganization between treatments. At the same time, trend tests and causal inference confirmed concentration-dependent effects and a direct association between exposure and biochemical dysfunction. The data suggest that necrotrophic exposure constitutes a functional pathway for MP redistribution in terrestrial environments, exerting systemic effects even in the absence of direct adult contact.