S. Mahunka szerk.: Folia Entomologica Hungarica 53. (Budapest, 1992)

the dipterous assemblages by human activity. In the course of studies another aspect also arose: how to deal with the populations of rare species? The faunistical results of collectings (species new for the Hungarian fauna) were published elsewhere (Papp 1992). All the voucher specimens are preserved in the collection of the Zoological Department, HNHM, Budapest (minutia-pinned, double-mounted, also those specimens which were originally kept in alcohol). Acknowledgements. I sincerely thank Dr. David Grimaldi (American Museum of Natural History, New York, U.S.A) and Dr. Gerhard Bächli (Zoologisches Museum, Universität Zürich-Irchel, Switzerland) for their help with some identifications. I wish to thank Dr. János Izsák (Department of Zoology, Berzsenyi College, Szombathely) for his helpful comments. . MATERIALS AND METHODS Baiting with fermenting fruits is one of the classical methods in drosophilid studies, so the literature on the results is vast (for a bibliographical review see Bächli and Rocha Pité 1982). Most of the studies of this kind in Europe was made by G. Bächli, who made not only extensive and interesting collectings but applied quantitative methods for population analysis. In 1988-90 apple-bait collections were made in four localities of low mountain creek valleys in N and NE Hungary at an altitude range from 250 to 400 m a.s.l. These four valleys are affected by tourism to some extent: least at Aggtelek, most strongly at Magyarkút. All the four sites are comparatively well known as regards the faunistics of dipterous flies, e.g. they are characterized by a peculiar black brachypterous fly, the only pleciid species of Hungary, namely Penthetria fiinebris Meigen, 1804 (= holosericea). The four sites are: Aggtelek, National Park: Aggtelek, Ménes-völgy [=valley], Medvés-kert (below coded with A): below Ménes-forrás [source] and to 150 m downstream; Bükk National Park; Miskolc, Garadna-patak völgye (below coded with B): 200300 m above the Hámori lake; Börzsöny Landscape Protection Area: Verőcemaros (changed to Verőce during the period of collectings), Magyarkút, Keskenybükki-patak völgye (below coded with M): out of the settlement (upstream); Pilis Landscape Protection Area: Visegrád, Apátkúti-völgy (below coded with V): 150 m upstream of the hunting-seat. When coding the samples, a letter for the site and five numbers for day (2), month (2) and year were used, e.g. A11090 is for the Aggtelek site on the 11th of September, 1990. Fermenting apple bait (smashed apple of various kinds with some sugar added and fermented in lukewarm water for more than a week) was put on 40 x 40 cm square plastic sheets within a 10 m range of the creeks. The distance of one collecting point to another was at least 10 m, bait was put down at 15 to 18 places (4 to 5 deciliters to each) to gain one sample. Exposure time was usually half an hour. Drosophilids were-sweep netted for a period of two to three hours (mostly for three hours). In cases when during this period less than 100 specimens were captured, the collecting period was prolonged. The soil temperature at a depth of 5 cm, the air temperature