Diversity, occurrence, and life characteristics of natural entomopathogenic nematode populations from La Rioja (Northern Spain) under different agricultural management and their relationships with soil factors

Natural entomopathogenic nematode (EPN) populations were surveyed in La Rioja (Northern Spain) during two consecutive years (2003–2005) to study their diversity, occurrence, and life characteristics under different agricultural management representing natural areas and perennial and annual crops from organic and conventional systems. Native EPN species and strains were identified using morphological and molecular characteristics. Virulence, infection cycle length and reproductive potential were assessed using Galleria mellonella larvae. The EPN occurrence was evaluated through abundance, recovery frequency, larval mortality percentage and EPN population density. EPNs were also related to selected soil physical and chemical variables as well as to some soil pollutants such as heavy metals and organochlorine pesticide residues. Only two steinernematids species were identified: Steinernema feltiae was observed throughout all seasons from natural and agricultural areas and Steinernema carpocapsae in summer and autumn of 2004 from perennial crops only. The virulence of native strains was lower than other previously isolated Spanish strain from natural areas or crop field edges. EPN abundance and recovery frequency indicated that habitat type might influence EPNs occurrence stronger than seasonality with the intensity of agricultural management inversely affecting their distribution. Moreover, clay, P2O5, Zn, Cu and hexachlorobenzene contents negatively correlating with EPN population density. We consider that agricultural management should be taken into account if EPNs are going to be used as biological control agents.