Background and aims As part of a research consortium that explores ways to improve soil health, we study how entomopathogenic nematodes (EPNs) can be better exploited for the biological control of soil-dwelling insect pests in annual crops. Methods We evaluated how tillage might affect belowground interactions in two 30-year running Swiss field trials by combining traditional (insect bait) and molecular (novel real-time qPCR protocols) methods. Soil samples (April and October 2013) were evaluated for the presence and activity of EPN soil food web assemblage comprising 13 EPN species, six nematophagous fungi, one ectoparasitic bacterium, and the free-living nematodes (FLN) of the Acrobeloides group. Results Mortality of sentinel larvae, as well as qPCR analyses (for which we provide seven new primers/ probes sets) found only trace levels of six EPN species, dominated by heterorhabditids species. Analysis of nematode progeny revealed that EPN compete intensely with FLN for insect cadavers. Overall, it appears that temperate annual cropping systems provide poor environments for EPN and that tillage does not negatively affect the natural occurrence of EPN. Conclusions Natural occurrence of EPN in Swiss tillage soils was very low, and augmentation may be a promising strategy to improve the control of root pests of annual crops.

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