Temporary changes in populations of soil organisms after field application of entomopathogenic nematodes

To assess the effect of an inundative release of entomopathogenic nematodes on soil organisms, population densities of soil-dwelling organisms were monitored before and after an application of an aqueous suspension of Heterorhabditis megidis to field plots in mown grassland (Exp. I) at a level of 0.38 million/m(2) and to plots (Exp. II) situated in a forested area, a grass sports field and an orchard at a level of 1.5 million/m(2). At the forested site, heat-killed H. megidis (1.5 million/m(2)) also were applied to two plots to compare the impact on soil organisms of a large introduction of living and dead nematodes. Post-treatment, temporary changes in natural population densities of several nematode genera and other organisms were detected in H. megidis-treated plots in both experiments. Temporary changes in the nematode trophic structure occurred in the percentages of nematode omnivores, herbivores and predators in both experiments. Evidence from all sites suggests that the changes were temporary and that the presence of decaying H. megidis following treatment contributed to nutrient enrichment of the soil and to direct and indirect effects on the nematode community.