Gypsy moth hemocytes phagocytosed and/or encapsulated walled entomophthoralean cells and protoplasts that were regenerating cell walls but rarely recognized the healthy protoplasts that lack cell walls. Experiments using lectin conjugates demonstrated different sugars localized at the surface of protoplasts, regenerating protoplasts, and walled cells. Protoplasts had few sugars, in small amounts, on their surfaces and these fungal cells evoked minimal cellular responses. Walled fungal cells had greater quantities of a variety of sugars in the cell walls and evoked the strongest defense response. Protoplasts of Entomophaga grylli, an orthopteran pathogen that cannot successfully develop in the gypsy moth, Lymantria dispar, evoked a stronger hemocytic response in larvae than protoplasts of the lepidopteran pathogen Entomophaga maimaiga that is able to successfully develop in L. dispar. Sugars detected at the surface of E. grylli and E. maimaiga protoplasts were similar, so it is likely that the surface sugars we tested do not determine the differences in nonpathogen recognition between these fungal species.