ACTA ZOOLOGICA BULGARICA Acta zool. bulg., 55 (2), 2003: 67-74 Entomopathogenic Nematodes of the Families Steinernematidae and Heterorhabditidae (Rhabditida) in the Vicinity of the Zheleznitsa Village, Vitosha Mts., Bulgaria Yassen Zh. Mutafchiev*, Denis P. Gradinarov* Abstract: The entomopathogenic nematodes were studied by the "nematode baiting" method in soils of grassland and Scotch pine (Pinus silvestris L.) stand in the region of Zheleznitsa Village in the Vitosha Mountain. Five species of the genus Steinemema Travassos, 1927, and one of the genus Heterorhabditis Poinar, 1976, were recovered. These are the species of both families found in the Vitosha Mountain: S. kraussei (Steiner, 1923), S. affine (Bovien, 1937), S. feltiae (Filipjev, 1934), S. carpocapse (Weiser, 1955), S. intermedium (Poinar, 1985) and H. bacteriophora Poinar, 1976 (Shishiniova et al., 1998; Gradinarov et al., 2000a). The nematodes were recovered in an equal percentage (33 %) of samples in the forest and meadow parts of the study area. The species S. intermedium and S. kraussei were isolated from forest soil, S. feltiae from forest and meadow, and the rest of the species - from meadow soil only. This confirms the previous data of the habitat specialization of these species in the Vitosha Mountain (Gradinarov et al., 2000b). The distribution of the detected species and the possible hosts is discussed. The preliminary results about coinvasion of model host Galleria mellonella larvae with pairs of isolated nematode species show that the development of each of the investigated species inhibits the development of the others. Key words: entomopathogenic nematodes, Steinernematidae, Heterorhabditidae, Bulgaria, Vitosha Mountain, coinvasion, competition Introduktion The entomopathogenic nematodes of the families Steinernematidae and Heterorhabditidae are obligate parasites of insects, mutually associated with insect-pathogenic bacteria of the genera Xenorhabdus and Photorhabdus. It is known that they are widely distributed in various habitats in Europe (Hominick, Briscoe, 1990; Miduturi, 1997; Mraček, Becvar, 2000). The different species show different preferences to the factors - climate, altitude, soil characteristics, vegetation and the presence of suitable hosts (Hominick, Briscoe, 1990; Mraček, Becvar, 2000). The present study aims at investigation of the (a) species composition of entomopathogenic nematodes (Steinernematidae, Heterorhabditidae) in the Zheleznitsa region of the Vitosha Mountain; (b) distribution of the recovered species in the investi- * Sofia University, Faculty of Biology, Department of Zoology and Anthropology, 8 Dragan Tsankov Blvd, 1164 Sofia, Bulgaria 67