Abstract:  In order to explore the mechanism of immunological and stress response of Ostrinia furnacalis Guenée larvae invaded by Escherichia coli, the numbers of total hemocytes, granular hemocytes and plasmatocytes in the 5th instar larvae of O. furnacalis injected with physiological saline, 3×10³, 3×10⁴, 3×10⁵ and 3×10⁶ cells/mL E. coli, respectively, were counted, and the activities of phenoloxidase (PO), glutathione peroxidase (GSH-px), glutathione-S-transferase (GST) and glutathione reductase (GR) were determined. The content of reactive oxygen species (ROS) of the hemocytes was also analyzed by flow cytometry (FACS). The results showed that the numbers of total hemocytes, granular hemocytes and plasmatocytes in the 5th instar larvae of O. furnacalis increased significantly in 12 h post injection with 3×10⁵ cells/mL and 3×10⁶ cells/mL E. coli (P<0.01), compared with the control group. The content of ROS in hemocytes also increased at the same time. Injections with 3×10⁴, 3×10⁵ and 3×10⁶ cells/mL E. coli triggered the enhancement of PO activity, and also induced the increase of the activities of GSH-px, GST, and GR in the serum. The results suggest that the abilities of cellular and humoral immunity of O. furnacalis larvae are significantly affected by the injection of E. coli, and the activities of GSH-px, GST and GR are also induced to scavenge the excessive ROS to prevent from the toxic effect of ROS.

Key words: Ostrinia furnacalis；Escherichia coli；hemocyte, phenoloxidase, antioxidant enzymes, reactive oxygen species