Suppression of nematophagous fungi by enchytraeid worms: a field exclosure experiment

Abstract

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 hypothesis that exclusion of enchytraeids, largely E. crypticus, would improve establishment of certain nematophagous fungi in field plots. The fungi, Hirsutella rhossiliensis and Monacrosporium gephyropagum, are being studied as potential control agents of plant-parasitic nematodes and were formulated as hyphae in alginate pellets. The pellets were mixed into soil without enchytraeids and placed in cages (PVC pipe, 80 cm volume) with fine (20 μm) or coarse (480 μm) 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 increased to large numbers. When coarse mesh was used, enchytraeid numbers in cages increased rapidly and the fungi did poorly. Although mesh also affected other potential fungivores, including collembolans and large dorylaimid nematodes, we suspect that enchytraeids were more important 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 important because the fungi did better in heat-treated soil than in non-heat-treated soil, regardless of mesh size. The rapid increase in enchytraeid numbers in cages with hyphal pellets and coarse mesh was probably caused by movement of enchytraeids toward the pellets with hyphae: increase in enchytraeid numbers was minimal when movement into cages was blocked (or when cages contained pellets without hyphae). Overall, the data were consistent with the hypothesis that enchytraeids, or other meso- or macrofauna, contributed to suppression of nematophagous fungi in our field plots.

Enchytraeids and Nematophagous Fungi in Tomato Fields and Vineyards

“…Based on field observations and field exclosure experiments, Jaffee et al (19) inferred that the efficacy of both fungi was reduced by enchytraeid worms. Indeed, enchytraeid reproduction increased dramatically when pelletized hyphae were added to soil (17).…”

“…Data implicating enchytraeids in the population dynamics of nematophagous fungi were obtained from only one soil, a very porous loamy sand located on the campus of the University of California at Davis (19). In the current study, I determined whether enchytraeids and certain other soil fauna affected pelletized H. rhossiliensis and M. gephyropagum in several commercial tomato fields and vineyards in California.…”

Functional and ecological consequences of saprotrophic fungus–grazer interactions

“…Network growth and development are key processes in the redistribution of nutrients within woodland soils (Cairney, 2005). By severing mycelia and ingesting growing hyphal tips, mycophagous collembola can restrict mycelial extension and high-intensity enchytraeid and woodlouse grazing can completely remove foraging Hirsutella rhossiliensis and Resinicium bicolor systems, respectively (Jaffee et al, 1997;Crowther et al, 2011a). As well as limiting the ability of foraging basidiomycetes to encounter new resources, grazing also disrupts the translocation of carbon (Butenschoen et al, 2007) and nitrogen (Tordoff et al, 2011) through mycelial systems.…”

Natural and released inoculum levels of entomopathogenic fungal biocontrol agents in soil in relation to risk assessment and in accordance with EU regulations

“…The feeding biology of enchytraeids is poorly understood as is their effect on EPF. Enchytraeids are known to feed on fungal propagules in the soil and contribute to suppression of nematophagous fungi (Jaffee, Santos, and Muldoon 1997). Dash, Nanda, and Behera (1980) studied the feeding preferences of three species of enchytraeids and noted that they ingested large amounts of organic material and fungi with fungal material constituting 30% of the gut contents.…”