Syrphid flies in natural grass ecosystems of some areas of the Kraishte region (Bulgaria) (Insecta, Diptera, Syrphidae) Emilia Markova Markova, E. (1997): Syrphid flies in natural grass ecosystems of some areas of the Kraishte region (Bulgaria) (Insecta, Diptera, Syrphidae). -Spixiana 20/1: 73-79 The structure of the syrphid communities in 6 natural grass ecosystems was studied. Basic population and cenotic characteristics -species composition, fre-quency of separate species, population density, dominant and trophical structure of the communities -were established. Four species of the established ones are new for the studied region. The most favorable ecological conditions for the syrphid communities are in the ecosystem of Breznik, the most unfavorable in the ecosystem of Pernik. Dr. Emilia Markova, Sofia University, Faculty of Biology, Department of Ecolo-gy, 8 Dragan Tasankov boul., 1421 Sofia, Bulgaria. Introduction This investigation is the second regional faunistic-ecological study on Syrphidae in the areas of Trun, Breznik, Divlya, Pernik, Kyustendil and Dupnitsa and deals with the natural grass ecosystems. In a previous study, Markova (1995) made an ecological analysis of the syrphid communities in different types of agroecosystems of the same region of Bulgaria. Material and methods The investigation was carried out in May, August, September and October 1990, and June, August and October 1991. Six natural grass ecosystems were studied. Their disposition is shown in Fig. 1. The material was collected by "mowing" with a Standard entomological sack. The number of samples taken from each ecosystem was 10 in 1990 and 20 in 1991. Each sample is the result of 50 mowing movements with an average length of 1 m. Different population and cenotic indexes were used to evaluate the Status of the syrphid cenoses. The taxonomic similarity, the similarity of population density of the species and the biocenotic similarity were evaluated after the Classification of Zlotin (1975). The frequency of the species was determined after Bodenheimer and Balogh (after Dazho 1975), but the dominant Community structure after Arzamasov et al. (after Hotko et al. 1982). The data were statistically processed in order to determine the total density of the syrphid flies. The biocenotic similarity was graphically presented by Cluster analysis (after Pesenko 1982). The region studied is mainly in the zone of the temperate Continental climate (Tishkov 1982, Georgiev 1985). The rainfall of this region is characterized by summer maximum and winter minimum. The area of Kyustendil is an exception because it belongs to the transitional continental climatic zone 73
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