Temporal study of natural populations of Heterorhabditid and Steinernematid nematodes in horticultural crop soils

Summary- The dynamics of natural populations of entomopathogenic nematodes in horticultural crop soils were studied via monthly sampling of eight sites in Catalonia (NE Spain) over 14 months. Entomopathogenic nematodes were found at six of the eight sites and they continued to be detected regardless of the agricuhural practices carried out at the sites. During the study these sites were ploughed, which destroyed the natural habitat of the nematodes, then left fallow for several months, but this did not have any significant effect on the presence of the nematodes. However, sorne seasonal fluctuations were observed with lower populations during the hotter summer months. This seasonality also appeared to affect the vertical distribution: the nematodes migrated tO deeper layers during summer, presumably to avoid the damaging effects of temperature and lack of humidity. The results of this study show that natural populations of entomopathogenic nematodes are capable of persisting and surviving for a long time in the soil, by adapting to the fluctuating and adverse conditions of their habitat. Résumé- Etude temporelle des populations naturel/es de nématodes Heterorhabditides et Steinerne1natides dans les sols horticoles- La dynamique des populations de nématodes entomopathogènes dans des sols horticoles a été étudiée par des prélèvements mensuels en huit sites de Catalogne (nord-est de l'Espagne) pendant 14 mois. Ces nématodes entomo-pathogènes ont été détectés dans six des huit sites et ont continué à l'être quels qu'aient été les traitements agricoles pratiqués sur ces sites. Pendant cette étude, les sites ont été Jabourés, détruisant ainsi J'habitat naturel des nématodes, puis laissés en jachère pendant plusieurs mois, sans que la présence des nématodes n'en paraisse affectée. Cependant, une influence saison