Abstract:

 In order to explore the effects of heavy metals on insect cellular immunity and its related mechanism, the differences in the number, viability, spreading and encapsulation rates, and morphology of hemocytes between the Cd²⁺ treated (at the concentration of 150 μg/g) Boettcherisca peregrina and its control were investigated and compared, respectively, using the methods as hemocytes counting, typan blue staining, spreading and encapsulation assays, as well as microstructure and ultrastructure observations. The results indicated that at 24, 48, 72 and 96 h post feeding the neonate larvae of B. peregrina with the artificial diet containing Cd²⁺, both total hemocyte count and hemocytes viability in the larvae were significantly decreased compared with the control, respectively. In contrast, the in vitro spreading rate and encapsulation capability of hemocytes of the larvae exposed to Cd²⁺ were significantly lower than those of the control after 72 and 48 h exposure, respectively, and then showed no significant differences with the control. Additionally, the in vivo encapsulation capability of hemocytes of the pupae that developed from the larvae exposed to Cd²⁺ was also significantly lower than that of the control. The morphological observation results showed that compared with the control, no marked alternation in the microstructure was observed for each type of hemocytes (including prohemocyte, plasmatocyte, granulocyte and oenocytoid), except that some plasmatocytes neither spread nor extended their pseudopods. However, the ultrastructure of each type of hemocytes in the exposed larvae was found to be alternated to various degrees compared to the control, with the main ultrastructural alternation including: damage or break of cell membrane, condensation of chromatin, sharply decreasing of the number of mitochondria, endoplasmic reticulum and other organelles, and the emergence of vacuoles in cytoplasm. The results suggest that heavy metal Cd²⁺ may have toxic effects on hemocytes of B. peregrina.

Key words: Boettcherisca peregrina, heavy metal pollution, cellular immunity, cadmium, hemocyte, encapsulation, microstructure, ultrastructure