The Effects of Entomopathogenic Fungus, Tolypocladium cylindrosporum on Cellular Defence System of Galleria mellonella

The entomopathogenic-fungus-life cycle is associated with the synthesis and secretion of a number of toxic metabolites, including extracellular enzymes and the low-molecular weight compound (toxin). The potential for a successful pathogen relies on the ability to overcome the various host-defence systems. Interaction between the fungus, Tolypocladium Deuteromycetes), its secondary metabolite, and its host cellular defence were investigated using in vivo and in vitro studies. In vitro studies showed that toxins (efrapeptins) inhibit phagocytic activity of Galleria mellonella (Lep: Pyralidae) haemocytes. The effect of efrapeptins on phagocytosis was in a dose-dependent manner i.e. the amount of phagocytosis in a treated cell-culture with 0, 3, and 30 μg efrapeptins per well was about 12, 7.5, and 4.5 %, respectively (P<0.05). In vivo studies showed that injection of insects with 0, 0.25, and 0.025 μg toxin rendered percentages of phagocytosis of 13, 11.5, and 7.2, respectively (P<0.05). There was no significant reduction in the total haemocyte count (THC) when larvae were injected with Tolypocladium cylindrosporum spores until 24 hours following injection. However, THC was suppressed at 48 hours post-treatment of larvae with spores. Considering that toxin suppresses phagocytosis, nodule formation, but not THC, this study suggests that efrapeptins may interfere with the ligand-receptor interactions that are likely to occur in the plasma membrane of specific haemocytes