Immunological and Genotoxic Effects of Polystyrene Microparticles on the Model Insect Tenebrio molitor L. (Coleoptera: Tenebrionidae)

Polystyrene (PS) is a widely used plastic that degrades slowly, leading to environmental accumulation as microplastics (PS-MPs, <5 mm). This study investigated the immunological and genotoxic effects of 1 µm PS-MPs at different doses (5, 10, 20, 40 mg/ml) on the larval stage of the yellow mealworm, Tenebrio molitor L. (Coleoptera: Tenebrionidae). Dietary exposure to PS-MPs resulted in increased larval and pupal developmental times and decreased larval, pupal, and adult weights compared to the control group. Significant alterations were observed in larval hemolymph, including changes in total hemocyte count, mitotic index, and the proportions of plasmatocytes, granulocytes, and oenocytoids, though prohemocyte levels remained unchanged. PS-MP exposure led to a dose-dependent increase in spreading, necrotic, and abnormal hemocytes, while apoptotic cell rates decreased at the highest dose. The encapsulation response of larval hemocytes decreased compared to controls. Melanization response regarding phenoloxidase activity in larval hemolymph increased with rising PS-MP doses. Comet assay results showed a dose-dependent increase in DNA damage in larval hemocytes following dietary exposure to PS-MPs. These findings indicated that exposure to low-sized (1 µm) PS-MPs induces changes in the innate immune defense of T. molitor larvae, highlighting potential cytotoxic and genotoxic effects. As a result, this study suggests that chronic exposure to low-sized PS-MPs can cause ecotoxicological effects on terrestrial insect species.