S. Mahunka szerk.: Folia Entomologica Hungarica 49. (Budapest, 1988)

FOLIA ENTOMOLOGICA HUNGARICA ROVARTANI KÖZLEMÉNYEK XLIX 1988 p. 5-11 Faunistical investigations on Ephemeroptera and Plecoptera along the Apátkút Stream, Visegrád Mountains,Hungary By S. ANDRIKOVICS (Received December 20, 1987) Abstract: 16 Ephemeroptera and 11 Plecoptera species were found along the Apátkut Stream. Along the stream Ecdyonurus starmachi (Sowa, 1971) occurred in large individual numbers, this species is proved to be new for the Hungarian fauna. Occurrence of Caenis luctuosa (Burmeister, 1839) is also new Hungarian datum. Among Plecoptera, Leuctra pseudosignifera is interesting, which has been found only in the Börzsöny Mountains so far. Leuctra digitata is also new for the fauna of the Visegrád Mountains. The Apátkut Stream can be found in the Visegrád Mountains, it flows from Pilisszentlászló (380 m) north-northeastwards along 9 kms length and meets the Danube at Visegrád at the river km no. 1695. It has a fall of 250 ms and gradient of 2. 73%. The main mass of the Visegrád Mountains is andésite, it dates from the M id dile--Miocene. In accordance with it, the stream-bed is formed by andésite-pebbles, breccia and the running of the stream is followed by agglomerates, tuff and lava rocks. Accumulation of detritus in bigger quantity can be found only seldom on parts having lower falling gradient and a more quiet flowing. Amount of constructive organisms in the stream is very small, allochthon materials have major importance in the energy economy flow (SIMONYI 1981). Downstream, on the right and left side water of three and four lesser stream are collected (Fig. 1). The subsidiary streams become dry during the summer, but the main stream is permanent. The average speed of the water is very high, it reaches as much as 1 ms" . The dissolved O2-content of the water is high, and its alteration depends mainly on pollution circumstances. At the source of the stream the 0

2-content is low, water is heavily polluted here. Farther down the cleansing of the water is indicated by a higher 0

2-content and on the lower parts, at Visegrád, the water is again polluted by communal waste materials, but the rate of pollution is a little bit lesser than it is at Pilisszentlászló (ANDRIKOVICS and HADNAGY 1988). Three types of substrate occur in the stream, in an arrangement according to the forming effects of waterspeed. On clear, sandy substrate larvae of aquatic insect are almost entirely absent. On places having low waterspeed the dissolved 0

2-content is relatively low and Ephemeroptera (Baetis rhodani

) and Limnephilidae (Trichoptera) larvae are more abundant here, in the detritus. On the stony parts of the stream waterspeed and the dissolved 0

2-content are the highest and the rhithron organisms are the most abundant both in species and individual numbers. Of the rich macrofauna of the stream, two groups were investigated: Ephemeroptera and Plecoptera. Reason for the investigation lies in the long lapse of time, since a comprehensive study about the Ephemeroptera and Plecoptera fauna was published at the end of the 1960s, but studies dealing with more detailed elaborations certain streams are almost totally lacking (ÚJHELYI 1959, 1966, 1969, STEINMANN 1968). This study was carried out in the organisation of the Ecological and Botanical Research Institute of the Hungarian Academy of Sciences, Vácrátót, by the aid of the Hungarian Academy of Sciences.