Observations on the Trapping of Nematodes by Dactylaria Scaphoides Using Optical, Transmission and Scanning-Electron-Microscopic Techniques

SUMMARY

The host-predator relationships between two nematodes, the free-living Panagrellus redivivus, the myceliophagous Aphelenchus avenae, and the predaceous hyphomycete Dactylaria scaphoides were investigated using light and scanning-electron microscopy of whole-mount preparations and transmission-electron microscopy of ultra-thin resin (Spurr) sections. The three-dimensional adhesive networks consistently trapped the nematodes under our experimental conditions. The reticulate traps were adhesive, but penetration was effected by appressoria produced on short hyphal branches from trapping hyphae. The infection process was very broad and produced a large infection bulb within the nematode from which infection hyphae developed. Chemical lysis appeared to function in the penetration process, with little evidence of mechanical pressure being involved. The matrix which bounds the infection process and the infection bulb of D. scaphoides is compared with the bounding structures in D. brochopaga and D. candida (constricting-ring and adhesive-knob-forming trappers respectively).