SUPPRESSION OF NEMATOPHAGOUS FUNGI BY ENCHYTRAEID WORMS - A FIELD EXCLOSURE EXPERIMENT

The feeding biology of Enchytraeus crypticus and other enchytraeids is poorly understood as is their effect on nematophagous fungi. Because enchytraeids had been associated with nematophagous fungi in the field and had suppressed these fungi in soil microcosms. we tested the hypo thesis that exclusion of enchytraeids, largely E. crypticus, would imp rove establishment of certain nematophagous fungi in field plots. The fungi, Hirustella rhossiliensis and Monacrosporium gephyropagum, are b eing studied as potential control agents of plant-parasitic nematodes and were formulated as hyphae in alginate pellets. The pellets were mi xed into soil without enchytraeids and placed in cages (PVC pipe, 80 c m(3) volume) with fine (20 mu m) or coarse (480 mu m) mesh, cages were buried 15 cm deep in field plots and then recovered after 6-52 days. When fine mesh was used, enchytraeids were excluded and the fungi incr eased to large numbers. When coarse mesh was used, enchytraeid numbers in cages increased rapidly and the fungi did poorly. Although mesh al so affected other potential fungivores, including collembolans and lar ge dorylaimid nematodes, we suspect that enchytraeids were more import ant because large numbers were consistently found in cages with coarse mesh soon after the cages were placed in soil. Organisms smaller than enchytraeids (bacteria, fungi, and protozoa) also appeared to be impo rtant because the fungi did better in heat-treated soil than in non-he at-treated soil, regardless of mesh size. The rapid increase in enchyt raeid numbers in cages with hyphal pellets and coarse mesh was probabl y caused by movement of enchytraeids toward the pellets with hyphae: i ncrease in enchytraeid numbers was minimal when movement into cages wa s blocked (or when cages contained pellets without hyphae). Overall, t he data were consistent with the hypothesis that enchytraeids, or othe r meso- or macrofauna, contributed to suppression of nematophagous fun gi in our field plots.