Survey of entomopathogenic nematodes from the families Steinernematidae and Heterorhabditidae (Nematoda: Rhabditida) in the Czech Republic

Soil samples were collected from the whole territory of the Czech Republic, and the presence of entomopathogenic nematodes from the families Steinernematidae and Heterorhabditidae was evaluated by Galleria traps method. Of the 342 samples studied, 53.8% were positive for entomopathogenic nematodes with only one positive for the heterorhabditid, Heterorhabditis megidis Poinar, Jackson et Klein, 1987. Of steinernematid species, Steinernema kraussei (Steiner, 1923), Steinernema feltiae (Filipjev, 1934), Steinernema affine (Bovien, 1937), Steinernema intermedium (Poinar, 1985), Steinernema bicornutum Tallosi, Peters et Ehlers, 1995, and Steinernema sp. belonging to “glaseri” group were recovered. With several exceptions the nematodes occurred in all the ecosystems, subecosystems and habitats studied. They were more frequently found in samples from tree than open habitats, from light than heavy soil, and their incidence was ubiquitous, rather than patchy. Dependence of entomopathogenic nematodes on insect incidence seemed to be elementary for both their incidence and abundance. The sampling sites with moderate to severe insect abundance were 66.5 % positive for nematodes while those with slight or no visible insect abundance only 15 %. Entomopathogenic nematodes from the families Heterorhabditidae and Steinernematidae are important parasites of insects with a wide host spectrum. Recently, these nematodes were successfully used as biological control agents of noxious insect species in agriculture, forestry etc. Therefore, there is a great scientific interest in understanding the nematode behaviour and natural incidence. Several studies have been published concerning their distribution in America (Mráček and Webster 1993), Australia (Akhurts and Bedding 1986) and Europe. Recently, these nematodes have been found also in South Asia (Mason et al. 1996) and Africa (Shamseldean and Abd Elgawad 1994). European entomopathogenic nematode mapping projects have provided a lot of data on nematode distribution mainly in western and northern Europe (Ehlers et al. 1991, Hominick and Briscoe 1990a, Steiner 1996, Vänninen et al. 1989, Haukeland 1993, etc.). The goal of this effort is to create a European grid of distribution of these nematodes, to determine the species, and to find general relationships with the soil type and preference of habitat type. These nematodes are widely distributed in Europe, but until now, not much was known about the distribution of heterorhabditids and steinernematids in Central (Mráček 1980) and Eastern (Mráček and Jenser 1988) Europe as well as about the significance of insect abundance associated with the incidence of entomopathogenic nematodes. Therefore, this study aims to survey entomopathogenic nematodes from the families Heterorhabditidae and Steinernematidae in the Czech Republic, to identify the species, preference of ecosystem, habitat, and soil type, and to study possible relationships between nematode incidence and insect abundance. MATERIALS AND METHODS Soil samples for our experiments were collected from the whole territory of the Czech Republic, and the presence of nematodes was evaluated by Galleria traps (Beding and Akhurst 1975, Mráček 1980). In 1996/1997 soil samples were taken from 342 sampling sites (Tables 1, 2). The sampling sites were targeted to areas with moderate or severe insect outbreaks (high incidence of defoliators or outbreaks reported by district agricultural services), and sites with no evident insect occurrence were chosen as the control sites. Collecting was performed throughout all seasons, but the number of soil samples from the winter season was low. Each soil sample was taken with an iron core (volume 200 cm), 5 cores per habitat (to get the constant volume of experimental soil), and transported to the laboratory