Deployment of Duddingtonia flagrans in an improved pasture system: dispersal, persistence, and effects on free-living soil nematodes and microarthropods

The environmental impact of Duddingtonia flagrans, a potential biological control agent for nematode parasites, was assessed in an improved pasture. Sheep feces containing D. flagrans and feces without D. flagrans were placed on pasture plots on four different occasions (series): May, August, November 1998, and February 1999. At 0, 1, 2, 4, 8, 16, and 24 weeks following fecal deposition, the persistence and dispersal of the fungus from the site of deposition were estimated. In addition, the impact of fungal presence on the numbers of non-target, free-living soil nematodes and microarthropods was assessed. For all four series, D. flagrans was not found outside the point of fecal deposition indicating that D. flagrans had not spread in the horizontal plane. D. flagrans was detected at the point of fecal deposition while intact fecal material was present and persisted for 8-24 weeks after initial contamination in association with the soil under the point of deposition. Over time, there was generally a decline in the number of positive observations of D. flagrans presence and the rate of this decline appeared to be seasonal. D. flagrans was observed in the top 10 cm layer of soil frequently, in the 10-20 cm soil layer occasionally, and in the 20-30 cm soil layer rarely. It is thought that rainfall and the activity of macroarthropods (in particular dung beetles) and earthworms may have contributed to this downward movement through the soil profile. Numbers of free-living soil nematodes and microarthropods at the point of fecal deposition varied considerably between samples but were not reduced by D. flagrans. There were no negative effects of fungal presence on the presence of other nematode-trapping fungi. The results of this study indicate that there were no detectable negative environmental impacts of D. flagrans use in a typical improved pasture.