Soil nematode assemblages indicate the potential for biological regulation of pest species

In concept, regulation or suppression of target nematode pest species should be enhanced when an abundance of predator species is supported by ample availability of bacterial- fungal- and non-damaging plant-feeding prey species. We selected soils from natural and managed environments that represented different levels of resource availability and disturbance. In microcosm chambers of each soil, in its natural state or after heat defaunation, we introduced test prey species not already resident in the soils (Meloidogyne incognita and Steinernema feltiae). Survival of the test prey was determined after a 5-day bioassay exposure. Across the soils tested, predator abundance and biomass were greater in undisturbed soils with plentiful resources and lower in soils from agricultural sites. Suppressiveness to the two introduced species increased with both numerical abundance and metabolic footprint of the predator assemblages. The magnitude of the increase in suppressiveness was greater at low numbers of predators then dampened to an asymptotic level at greater predator abundance, possibly determined by temporal and spatial aspects of the bioassay system and/or satiation of the predators. The more resource-limited the predators were and the higher the metabolic predator footprint, the greater the suppressiveness. The applied implications of this study are that soil suppressiveness to pest species may be enhanced by increasing resources to predators, removing chemical and physical constraints to their survival and increase, and altering management practices so that predators and target prey are co-located in time and space.