Ábrahám Levente: Biomonitoring a Dráva folyó magyarországi szakasza mentén 2000-2004 - Natura Somogyiensis 7. (Kaposvár, 2005)
Uherkovich, Ákos - Nógrádi, Sára: Middle-term changes in caddisfly (Trichoptera) communities of the Hungarian part of Drava river during the years 1992–2004 - Tegzes együttesek középtávú változásai a Dráva magyarországi szakasza mentén, 1992-2004 folyamán
50 NATURA SOMOGYIENSIS Method and materials During the last thirteen years we visited many sites along Dráva river several times. Besides the occuring species we always ascertained and made notes about the quantity of each species, thus all the samples were quantitative or near quantitative. The site Vízvár (XM70; 17°13'30" E, 46°05'15" N) is known very well, as between 1992 and 2004 we collected there yearly. Here the river runs in its natural bed, some branches formed during times, and many shoals formed and changed year by year. Maybe this is the most valuable section of the river owing to its ancient state (Figs. 2-3). The quantitative results of some years (1992, 1994-1999) were not satisfactory, as we visited the site only a few times. In 1993 and during the years 2000-2004 we sampled there with good results, as those samples contains thousands of caddisflies (Fig. 1). During these thirteen years altogether 20 675 specimens of 60 species were determined from the samples (see Table 1). In some years we did not take larger samples but only occasional ones with few adults (1992, 1994-1998), while in the other years fruitful night capturings were carried out, in 1993 and mostly since 1999 (Fig. 4). There were some other sites, where we collected larger materials, but we did not visited those regularly. In Drávapalkonya (BR87; 18°11'35" E, 45°47'15" N) and Vejti (YL37; 17°59'00" E, 45°47'35" N) we collected several times in the first half of the nineties. At Drávasztára (YL17; 17°49'45" E, 45°48'40" N) we collected in many years during the period 1992-2004, but not in all years (Fig. 6). The river was regulated at these sites more than a century ago: many bends were cut, thus the bed became shorter. The samples collected in three sites contain about 24 000 caddisfly adults in this period. We also visited some sites a little bit farther from the river, e.g. Bares and Darány environs, the "Bares Juniper Woodland" (XL99; 17°33'25" E, 45°59'35" N) , where we collected many times near a forest fen (Fig. 5). In this site a very different fauna formed. These series of collections were uneven in every sites. It is fact that the circumstances of collections always influence the species composition and mostly the number of adults considerably. The main factor is the actual meteorological situation. The activity depends on the temperature, humidity, clouds and over all the meteorological fronts. Prior to cold fronts, when the air pressure is falling, the activity of insects shoots up considerably. After the passing through of the front, the activity reduces immediately. The intensity of moonlight (i.e. the moon phase) can also influence the activity. The effect of most factors are unforeseenable in collections. Fig. 1.: The number of caddisfly adults taken at site Vízvár, 1992-2004. 1. ábra: A fogott tegzes imágók példányszáma Vízvárnál, 1992-2004.
