Immunological effects of polystyrene microparticles on the larval stage of the model insect Tenebrio molitor L. (coleoptera: tenebrionidae)

Polystyrene (PS) is a type of plastic that degrades slowly and accumulates widely in the environment in the form of microplastics (PS-MPs, >5 mm). This study aimed to investigate the immunological effects of different doses (5, 10, 20, 40 mg/ml) of 1 µm PS-MPs on the yellow mealworm, Tenebrio molitor L. (Coleoptera: Tenebrionidae), a model organism. Exposure to PS-MPs through the diet resulted in increased larval and pupal developmental times but decreased larval, pupal, and adult weights compared to the control group. PS-MP exposure altered total hemocyte count, mitotic index, and the levels of plasmatocytes, granulocytes, and oenocytoids in larval hemolymph, while prohemocyte rate unchanged. The rate of spreading, necrotic, and abnormal hemocytes increased with an increasing PS-MP dose, whereas the level of apoptotic cells decreased at the highest dose. The encapsulation response of larval hemocytes decreased compared to the control. While no significant change was observed in the total protein content of larval hemolymph, phenoloxidase activity in hemolymph increased with an increasing PS-MP doses. Comet assay results revealed a dose-dependent increase in DNA damage in the larval hemocytes. All data obtained in this study indicate that exposure to low-sized (1 µm) PS-MPs at increasing doses alters the innate immune defense of model and economic insect T. molitor larvae, while also causing cytotoxic and genotoxic effects.