TRAP PRODUCTION BY NEMATOPHAGOUS FUNGI GROWING FROM PARASITIZED NEMATODES

Nematode-trapping fungi are generally considered facultative parasites that produce traps only under special conditions. However, Arthrobotrys dactyloides, A. oligospora. Monacrosporium ellipsosporum, and M. cionopagum produced many traps when growing from parasitized nematodes in saturation extracts of four soils. Thus, conditions that induce traps may normally prevail when these fungi grow from nematodes in soil, and parasitism may be more important to these fungi than has previously been recognized. Whereas Hirsutella rhossiliensis (an endoparasitic fungus) produced infective structures only in the atmosphere, the trapping fungi produced infective structures when submerged and noninfective spores in the atmosphere; therefore, allocation of resources to traps or spores may be affected by soil water. When introduced into untreated loamy sand (8.0% moisture, -25 kPa) in the form of parasitized nematodes, H. rhossiliensis, M. ellipsosporum, and A. dactyloides parasitized significant proportions of assay nematodes (Heterodera schachtii); these fungi parasitized fewer nematodes if the soil was disturbed before the assay nematodes were added. In contrast, parasitism of assay nematodes by A. oligospora and M. cionopagum was not detected in the loamy sand.