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, Tolypocla-dium (Deuteromycetes), its secondary metabolite, and its host cellular defence were inves-tigated 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 phago-cytosis in a treated cell-culture with 0, 3, and 30 g 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 g toxin rendered percentages of phagocytosis of 13, 11.5, and 7.2, respec-tively (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 fol-lowing 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.