Eat or be eaten: fungus and nematode switch off as predator and prey

Use of the parasitic nematode Deladenus siricidicola to control invasive pine-killing Sirex noctilio woodwasps in the Southern Hemisphere is one of the most successful examples of classical biological control. Both nematode and woodwasp rely on the white rot fungus, Amylostereum areolatum, for continued survival, and the nematode is commercially mass produced in its mycophagous phase on this fungus. We tested the hypothesis that a role reversal can occur wherein fungal hyphae invade and kill nematode eggs. Deladenus siricidicola eggs were exposed to A. areolatum to quantify the number of eggs lost to fungal invasion. Additionally, A. areolatum and A. chailletii were observed via cryogenic scanning electron microscopy and fluorescence microscopy to document their ability to parasitize eggs and adults of D. siricidicola, D. proximus, and an undescribed Deladenus species. This study reports evidence of a basidiomycete destroying nematode eggs, as well as a novel trapping mechanism used to capture and parasitize three species of adult female Deladenus nematodes.