Interactions of Spodoptera littoralis haemocytes following injection with the entomopathogenic fungi: Beauveria bassiana and Nomuraea rileyi

Abstract

This study compared the cellular interactions of Spodopteralittoralis haemocytes with two virulence-different entomopathogenic fungi: Beauveriabassiana and Nomuraearileyi. Using light and transmission microscopy, five types of haemocytes namely, prohaemocytes (PRs), plasmatocytes (PLs), granulocytes (GRs), spherule cells (SPs) and oenocytoids (OEs) were identified in the 6th instar larvae. PRs and PLs were found in the haemopoietic tissue. Intra-haemocoelic injection of blastospores induced ultrastructural alterations in the cytoplasm and nuclei of circulating haemocytes of treated larvae. Different responses were observed in the populations of haemocyte types following injection with the tested fungi. The most important changes were the decrease of the numers of GRs accompanied with increase in SPs at 12-48h following injection with B. bassiana, whereas, a decrease of PLs with a commitment increase inSPs and OEs were observed at most time intervals after injection with N. rileyi. Both fungi provoked a decrease of the total number of haemocytes at 48h followed by an increase at 72h post-injection. In vivo assay showed that the GRs and PLs actively phagocytised fungal blastospores. There was a time-dependent decrease and increase in the phagocytosis activity after injection of B. bassiana and N. Rileyi, respectively. In B. bassiana-injected insects, the numbers nodules increased significantly at 6-48h in comparison with the controls post-injection. In N. rileyi-injected insects, nodules increased significantly only at 72h post-injection. No cellular encapsulation was observed in any of the examined insects.