Non-target effects of entomopathogenic nematodes on the soil nematode community.
There is growing awareness that biological control carries risks as well as benefits, but there are few data on below-ground effects of inundative insect pathogens. We addressed this issue using entomopathogenic nematodes and the soil nematode community in a turfgrass ecosystem as a model. The turfgrass ecosystem, located in Medina County, Ohio, USA, was composed of approximately 40% kentucky bluegrass (Poa pratensis), 30% perennial ryegrass (Lolium perenne) and 20% annual blue grass (P. annua). The remaining 10% of the vegetation was a mixture of annual grasses and broad-leaf weeds. Application of Heterorhabditis bacteriophora strain GPS11, H. bacteriophora strain HP88 and H. indica strain LN2 significantly reduced the abundance, species richness, diversity and maturity of the nematode community by reducing the number of genera and abundance of plant-parasitic, but not free-living, nematodes. Our results are the first to indicate selective suppression of plant-parasitic nematodes by entomopathogenic nematodes, H. bacteriophora and H. indica, with no adverse effect on free-living nematodes. In contrast to the entomopathogenic nematode treatments, trichlorfon (a commonly used insecticide in turfgrass) reduced the number of genera, abundance and diversity of the nematode community by adversely affecting both plant-parasitic and free-living nematodes. The reduction in abundance and diversity of plant-parasitic nematodes without any adverse effect on free-living nematodes that play a role in nutrient cycling, can be considered as a beneficial non-target effect of entomopathogenic nematodes.