INHIBITION OF PHAGOCYTIC-ACTIVITY OF PLASMATOCYTES ISOLATED FROM GALLERIA-MELLONELLA BY ENTOMOGENOUS FUNGI AND THEIR SECONDARY METABOLITES

The phagocytic activity of isolated plasmatocytes from Metarhizium ani sopliae- or Beauveria bassiana-infected Galleria mellonella larvae was examined and compared to that observed from untreated larvae, Mycosis reduced plasmatocyte phagocytic activity against either yeast cells o r blastospores of both entomopathogenic fungi, In contrast, the phagoc ytic activity of isolated plasmatocytes from diseased larvae against h ydrophilic silica beads was only moderately inhibited compared to cont rols, In addition, the influence of solubilized or surface bound funga l secondary metabolites from M. anisopliae (destruxin A and E, cytocha lasin B and D) on plasmatocytes in monolayers was investigated. Fungal cyclic peptides dissolved in sublethal concentrations were found to i nhibit phagocytic activity of plasmatocytes in a dose-dependent manner . Fungal blastospores coated with secondary metabolites were not inges ted, The phagocytic activity of plasmatocytes obtained from larvae whi ch were preinjected with sublethal concentrations of destruxin A was n ot significantly reduced, The corresponding inhibition of phagocytic a ctivity found in toxin-treated plasmatocytes in vitvo and in plasmatoc ytes isolated from infected larvae support the assumption that entomop athogenic fungi release secondary metabolites to impair the cellular r ecognition and defense reactions of their host. (C) 1997 Elsevier Scie nce Ltd.