A multimethod approach improves the description of the entomopathogenic nematode distribution in corn fields

International audience

English. Entomopathogenic nematodes (EPNs) are ubiquitous since they are distributed in all continents except in Antarctica. In agricultural soils, they offer a high potential for crop protection against insect pests. In France, few studies have so far described their distribution in field crops. The objective of this study is to combine several methods to improve the detection of EPNs in cultivated soils (Figure 1). We have first used multiple Galleria mellonella-baiting cycles on soil samples collected in 43 fields cultivated in corn during early summer (2021) in Southwestern France. The emergent nematodes were identified by sequencing of the ITS region. We obtained 28% of positive plots and baited 78 isolates belonging to three species: Steinernema carpocapsae, Steinernema feltiae, Heterorhabditis bacteriophora. We showed that the multiple G. mellonellabaiting cycle method during a period of time extending to 90 days, doubles the number of positive plots and increases the number of isolates by plot. On these 43 soil samples, we also performed soil-direct nematode extraction by Oostenbrink elutriation followed by water attraction of alive nematodes. After morphometric identification of EPNs in these nematode-extracted samples, we obtained 9.3 % positive plots. We are currently carrying out quantitative PCR tests for specific detection of EPNs in these nematode-extracted samples. With the combination of those different methods, we hope to describe a more accurate inventory of EPNs present in cultivated soils. This approach may allow improvement of our knowledge on the distribution of autochtonous EPNs in cultivated soils and their potential use to control insect pests.