## CHANGES IN THE BLACK FLY COMMUNITIES (DIPTERA, SIMULIIDAE) OF THE DANUBIAN INLAND DELTA

#### Daniela ILLESOVA1, Viera STLOUKALOVA2

1Institute of Zoology, Slovak Academy of Sciences, Dubravska cesta 9, 84206 Bratislava, SLOVAKIA
2Department of Zoology, Faculty of Natural Sciences, Mlynska dolina B1, 842 15 Bratislava, SLOVAKIA

CONCLUSIONS In spite of the generally good knowledge of black fly fauna, wery little data relates to large Slovak rivers. No doubt, among these belongs the Danube river, the section of rkm 1879.5 - 1712. Data collected from Danubian Lowland, intravilan of Bratislava, and Zitny ostrov were published by Jedlicka [5], Halgos & Jedlicka [1, 2] and Illesova [3].

During the years 1991-1994, 21 species of black flies were found at sites of the monitoring network along the Danube River inland delta. Of these, 12 species were recorded for the first time at this section of the Danube. The species Simulium balcanicum and Simulium reptans were dominant at all sampling sites. The species Prosimulium rufipes, Simulium auricoma found in 1993 and Simulium monticola found in 1994 are new members of the Danube river fauna. The presence of the species Prosimulium hirtipes, P. rufipes, P. tomosvaryi, Simulium argyreatum, S. degrandei, S. reptans, and S. colombaschense suggests sub-montaneous in montaneous character of this section of the Danube river.

The species diversity significantly decreased in the year 1993 at three monitored localities; Dunajske kriviny, Bodicka brana, and Istragov. The diversity of species at the locality of Klucovec was steady in the years 1993 and 1994, and in comparison with the year 1992 we recorded it increase.

#### MATERIAL AND METHODS

This study is based on the material collected during the years 1991-1994 at four locations inside the Danube inland delta; Dunajske kriviny (rkm 1840), Bodicka brana (rkm 1830), Istragov (rkm 1817), and Sporna sihot (rkm 1804).

The preimaginal stages of black flies were collected from June 1991 to October 1992 and from February 1993 to November 1994, once a month during winter, twice a month during the period from April to October. Individual collection of larvae and pupae from stones, plants, twigs and plastic garbage, was used. Because preimaginal stages of black flies prefer living in colonies, the determination of their relative quantity is not simple. Our experience, however, showed that picking in the selected stand, during atime of not greater than 20 minutes, is sufficiently representative. Stabilised microscopic slides have been made from part of the material by dehydration with phenol and then embedded in Canadian balsam.

#### RESULTS

21 species of black flies were found on the localities listed in the sectin Material and methods. These represent 45.6 % of species found in the territory of Slovakia. The following 12 species have been recorded at studied sections of the Danube river for the first time: Prosimulium hirtipes, P. rufipes, P. tomosvaryi, Simulium auricoma, S. variegatum, S. monticola, S. argyreatum, S. argenteostriatum, S. noelleri, S. degrangei, S. morsitans, S. voilense.

#### EVALUATION OF INDIVIDUAL LOCALITIES

#### Dunajske kriviny

This locality exhibited the greatest number of recorded species (19), during the four years of investigation (Tab. 1). The greatest diversity of species as well as the number of species (15), were recorded in the year 1992, hence before the diversion of the Danube main stream. After November 1992 expressive changes occurred in this locality. After a decrease in the water level, almost half of the original gravel river bottom had been exposed and the flow velocity had decreased. 15 species of black flies were recorded with less diversity than in the year before. In 1994 already 10 species were recorded. Only four common species were found in every year of investigation, namely Simulium balcanicum as an eudominant species, Simulium reptans as dominant/eudominant, Simulium equinum and Simulium erythrocephalum as subrecessive. The first mentioned had been known only from a few localities in southern Slovakia [7]. Therefore we did not expect such great euconstant and eudominant occurrence at other localities. Simulium reptans is, in Slovakia, a characteristic species for hyporhitral of submontaneous rivers and rivers in valleys [8]. The same characteristics fit also for the species Simulium equinum. Only several individuals of the species Simulium erythrocephalum, typical for majority of Slovak lowland rivers, was recorded. Despite the decrease in both the water level and the flow velocity in the year 1994, no impact occured to its abundance. The occurrence of the species Simulium degrangei at this locality in the years 1992 and 1993 is interesting from the faunal point of view, because it is a rare species, and were known at only two localities in the territory of Slovakia in the past [7]. We did not succeed in finding this species at this locality in the year 1994, similarly we failed in finding S. argenteostriatum, S. colombaschense, and S. voilense. The occurrence of S. colombaschense was not confirmed at other Slovak rivers except the Danube River. Another faunal rarity of this locality is the occurrence of the species Prosimulium rufipes in May 1993, which normally inhabit the submontaneous and montaneous regions of Slovakia. The Danubian region is the lowest situated locality where it occurs. The species Simulium monticola found at this locality in May 1994 is a completely new member to Danubian fauna. This species is typical for montaneous and submontaneous regions [9]. The species Simulium morsitans, known for requiring a high concentration of oxygen dissolved in water, was recorded as subdominant in 1992, though not confirmed in 1993, and was subrecessive in 1994.

After the diversion of the Danube the diversity of species at the locality of Dunajske kriviny had decreased and expected changes were manifested by the absence of species demanding a higher water flow velocity.

#### Bodicka brana

The sampling site at this locality is situated at a place of the former main stream of the Danube river at the end of the first flow concentration by the regulating dikes (groynes). The substrate for black flies consists of stones, boulders, trapped woods, logs and macrophytes as well as plastics, which we placed into the stream for this purpose. We recorded 16 species during the four years of monitoring at this locality. In the years 1992, 1993, and 1994, 6, 7, and 10 species of black flies were recorded, respectively. Simulium balcanicum, occurring throughout the year, is eudominant. Species S. erythrocephalum is subrecessive. S. equinum is subrecessive/subdominant. Species Simulium noelleri, subdominant in 1992, was found in the through-flowing side arms of Bodicka brana, where it has ideal conditions for development at the downstream gates, though, it was not confirmed in the former main stream. From the faunal point of view the unique occurrence of S. auricoma in the year 1993 was very interesting. Its individual occurrences in the East Slovakia are reported by Jedlicka [7]. The good conditions for development at this locality had found the species S. argenteostriatum, S. degrangei, S. colombaschense, S. voilense being subrecessive in the community of black flies. This is the only locality where Simulium vernum was not recorded.

#### Istragov

This locality is situated at the former main stream of the Danube river. During the years 1991 and 1992 we found 12 species of black flies. In these years the species Simulium vernum and Simulium vulgare were actually found only at this sample site in the whole monitoring area. Eudominant was found to be S. balcanicum and S. reptans, and in the year 1991 also S. lineatum. In 1992 we confirmed the occurrence of 8 species of black flies, S. balcanicum, S. equinum, S. erythrocephalum, S. ornatum, S. argenteostriatum, S. morsitans, S. reptans, and S. colombaschense. Conditions had significantly changed after the redirection of the main stream. An extensive decrease of water level at this locality caused, with one exception, improper conditions for the development of black flies. In 1993 only S. balcanicum remained.

In 1994 only two samples from this locality were positive, both in May during the higher water level in the Danube River and flooded vegetation at river banks. This vegetation served as a base for the development of preimaginal stages. In other months, simultaneously with the water level decrease, and also the flow velocity, which limits the black flies' development, markedly decreased. It is worth to mention here that black fly females do select breeding sites visually [10] and with certainty do recognise proper flow velocity. The increase of the diversity of species in 1994 can be just temporary, therefore this locality needs further monitoring.

#### Sporna sihot

This locality is situated at the main stream of the Danube. Altogether 9 species of black flies were recorded there. Eudominant species are Simulium balcanicum and S. reptans. In the year 1992 three species were found, namely S. balcanicum, S. equinum, and S. reptans. In 1993 in addition to this occurred S. lineatum, S. erythrocephalum, and S. argyreatum. The occurrence of the species S. balcanicum, S. lineatum, S. erythrocephalum, and S. reptans was confirmed in 1994. In addition new species, S. ornatum and S. morsitans, appeared, but only in low abundance. This locality, in contrast to above described, is not affected by the water engineering work at Gabcikovo.

#### GENERAL EVALUATION

The overall examination of all monitored areas (four localities at the main stream of the Danube River at rkm 1840, 1830, 1817, 1804), taking into consideration monitored families of black flies (Simuliidae), registered a decrease in the number of species from 15 in 1993 down to 10 in 1994. While the occurrence of two species of the family Prosimulium had been confirmed, namely P. hirtipes and P. tomosvaryi, typical Danubian species S. colombaschense, which has not yet been recorded in the territory of Slovakia outside the Danube [2], as well as the species S. voilense, were confirmed in 1994 only at the locality of Bodicka brana. The species S. equinum has only a rare occurrence. Another such species is S. morsitans, however its frequency at localities along the Danube river considerably fluctuates. In 1994 we found five individuals of this species. In contrast, S. morsitans was abundant at through-flowing side arms at Sulany and at Bodicka brana. Its occurrence is limited by the concentration of dissolved oxygen in the water. Knoz [9] classified it as a species inhabiting lowland rivers. However, there is only a litle data on the territory of Slovakia [6]. It was confirmed in the Danubian lowland by Illesova [3].

Typical species of the majority of Slovak lowland rivers (and whole of the Europe), S. erythrocephalum, is euconstant in the inland waters of Zitny ostrov and in the whole area of the Danubian lowland. At the monitored section of the Danube river, however, it occurred in 1994 at localities of Dunajske kriviny and Bodicka brana, as well as in Klucovec, as a subrecessive species. Besides other facts, this is evidently in opposition to its importance as a blood-sucking species [1, 8].

S. ornatum s.l., which is definitely in Slovakia the most wide-spread species of black flies (Jedlicka, 1978), was recorded only seldom in the Danube River and it was only an auxiliary element of fauna in the years 1991 and 1992. It was not recorded in the Danube at all in 1993 and had only a low frequency at all localities of occurrence during the year 1994.

Other recorded species, S. argenteostriatum and S. degrangei, are accessoric in the Danube River. They were confirmed only at Bodicka brana. This locality preserved its original character in 1994, which is confirmed also by the occurrence of the above mentioned species.

#### REFERENCES

  [1] Halgos, Jedlicka, L., 1971: The black-flies (Diptera, Simuliidae) attacking horses in the environs of Bratislava. Biológia (Bratislava), 26, p.431-433

  [2] Halgos, Jedlicka, L., 1987: Faunistical notes: Diptera, Simuliidae: Simulium colomaschense Biológia (Bratislava(, 42:1026

  [3] Illesova, D., 1992: Black-flies (Diptera, Simuliidae) of Zitny ostrov on Podunajska nizina Lowland. Biológia (Bratislava) 47, p.107-122.

  [4] Jedlicka, L., 1970: Die Verbreitung der Kriebelmücken (Diptera, Simuliidae( in der Südslowakei. Acta Rer. Nat. Slov. 16 (1(:45-46

  [5] Jedlicka, L., 1978: Distribution of Odagmia ornata Meigen, 1818 and Odagmia spinosa Doby et Deblock, 1957 (Diptera, Simuliidae) in Slovakia. Acta F.R.N. Univ. Comen. - Zoologia, 23,p. 81-89.

  [6] Jedlicka, L., 1981: Kratke faunisticke spravy: Diptera, Simuliidae: Chelocnetha latigonia, Simulium morsitans. Biológia (Bratislava), 36:1061

  [7] Jedlicka, L., 1984: Simuliidae In: Cepelak, J.(Ed.): Diptera Slovenska I, p.74-83, 242-243, Veda Bratislava,288p

  [8] Jedlicka, L., 1988: Types of black fly breeding places in Slovakia (Diptera, Simuliidae). Wiadomosci parazytol., 28:37-40

  [9] Knoz, 1965 To Identification of Czechoslovakian Black-Flies (Diptera, Simuliidae). Folia Fac. Sci. Natur. Univ. Purkynianae Brunensis, Biol. 2 (6) (5): 1-54 + 425 figs.

  [10] Timm, 1994: Reasons for the shift in dominance between Simulium (N( vernum and Simulium (S( ornatum (Diptera: Simuliidae( along the continuum of an unpolluted lowland stream. Arch. Hydrobiol. 131, 2, p. 199(210

Tab. 1. The abudance of back fly species on investigated localities during the years 1991-1994

Localities | Dobrohost | Bodicka brana | Istragov | Klucovec
--- | --- | --- | --- | ---
Species | 1991 | 1992 | 1993 | 1994 | 1991 | 1992 | 1993 | 1994 | 1991 | 1992 | 1993 | 1994 | 1991 | 1992 | 1993 | 1994
1. Prosimulium hirtipes |  | 5 | 3 | 1 |  | 1 |  |  |  |  |  |  |  |  |  |
2. Proaimulium rufipea |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |
3. Prosimulium tomosvaryi |  | 1 | 6 | 1 |  | 2 |  |  |  |  |  |  |  |  |  |
4. Simulium vernum |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
5. Simulium equinum | 1 | 4 | 1 | 2 | 2 | 4 | 1 | 4 |  | 4 |  |  |  | 2 |  |
6. Simulium lineatum |  | 4 | 1 |  | 3 |  |  |  | 47 |  |  |  |  |  |  |
7. Simulium balcanicum | 388 | 745 | 766 | 341 | 136 | 452 | 480 | 411 | 100 | 109 | 10 |  | 43 | 96 | 20 | 16
8. Simulium auricoma |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |
9. Simulivm erythrocephalum | 2 | 5 | 4 | 3 | 2 |  |  | 1 |  | 1 |  |  |  |  |  | 1
10. Simulium ornatum | 1 | 2 |  | 1 |  |  |  |  | 3 | 1 |  |  |  |  |  |
11. Simulium variegatum |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |
12. Simul.ium monticola |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |
13. Simulium argyreatum |  | 3 | 2 |  | 1 |  |  |  |  |  |  |  |  |  |  |
14. Simuluim axgenteostriatum |  | 7 | 5 |  |  |  |  | 5 |  | 1 |  |  |  |  |  |
15. Simulium vulgaxe |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
16. Simulium noelleri |  |  | 1 |  |  | 20 |  |  |  |  |  |  |  |  |  |
17. Simaulium degrangei |  | 2 | 4 |  |  |  |  | 1 |  |  |  |  |  |  |  |
18. Simulivm morsitans |  | 26 |  | 1 |  |  | 1 |  |  | 1 |  |  |  |  |  |
19. Siaulium reptans | 7 | 129 | 81 | 76 | 5 | 14 | 1 | 13 | 14 | 37 |  |  |  | 33 |  | 15
20. Simulium colombaschenee | 14 | 13 | 4 |  | 16 |  |  | 1 | 9 | 7 |  |  |  |  |  |
21. Simulium voilense |  | 9 | 1 |  |  |  |  | 3 | 8 |  |  |  |  |  |  |
Total | 413 | 958 | 880 | 426 | 165 | 493 | 484 | 439 | 183 | 181 | 10 | 0 | 43 | 131 | 20 | 32
H | 0,29 | 0,871 | 0,548 | 0,617 | 0,33 | 1,09 | 0,9 | 1,29 | 1,2 | 0,9 |  |  |  | 0,638 |  | 0,8

Tab. 2. The dominance of back fly species on investigated localities during the years 1991-1994

Localities | Dobrohost | Bodicka brana | Istragov | Klucovec
--- | --- | --- | --- | ---
Species | 1991 | 1992 | 1993 | 1994 | 1991 | 1992 | 1993 | 1994 | 1991 | 1992 | 1993 | 1994 | 1991 | 1992 | 1993 | 1994
1. Prosimulium hirtipes |  | 0,52 | 0,34 | 0,23 |  | 0,21 |  |  |  |  |  |  |  |  |  |
2. Proaimulium rufipea |  |  | 0,11 |  |  |  |  |  |  |  |  |  |  |  |  |
3. Prosimulium tomosvaryi |  | 0,1 | 0,68 | 0,23 |  | 0,41 |  |  |  |  |  |  |  |  |  |
4. Simulium vernum |  |  |  |  |  |  |  |  | 0,55 |  |  |  |  |  |  |
5. Simulium equinum | 0,24 | 0,48 | 0,11 | 0,46 | 1,21 | 0,81 | 0,21 | 0,91 |  | 2,48 |  |  |  | 1,53 |  |
6. Simulium lineatum |  | 0,48 | 0,11 |  | 1,82 |  |  |  | 25,68 |  |  |  |  |  |  |
7. Simulium balcanicum | 93,95 | 77,76 | 87,05 | 80 | 82,42 | 91,68 | 99,16 | 93,62 | 54,64 | 67,7 | 100 |  | 100 | 73,28 | 100 | 50
8. Simulium auricoma |  |  |  |  |  |  | 0,21 |  |  |  |  |  |  |  |  |
9. Simulivm erythrocephalum | 0,48 | 0,52 | 0,45 | 0,9 | 1,21 |  |  | 0,23 |  | 0,62 |  |  |  |  |  | 3,1
10. Simulium ornatum | 0,24 | 0,21 |  | 0,23 |  |  |  |  | 1,64 | 0,62 |  |  |  |  |  |
11. Simulium variegatum |  | 0,31 |  |  |  |  |  |  |  |  |  |  |  |  |  |
12. Simul.ium monticola |  |  |  | 0,23 |  |  |  |  |  |  |  |  |  |  |  |
13. Simulium argyreatum |  | 0,31 | 0,22 |  | 0,61 |  |  |  |  |  |  |  |  |  |  |
14. Simuluim axgenteostriatum |  | 0,73 | 0,57 |  |  |  |  | 1,21 |  |  |  |  |  |  |  |
15. Simulium vulgaxe |  |  |  |  |  |  |  |  | 0,55 |  |  |  |  |  |  |
16. Simulium noelleri |  |  | 0,11 |  |  | 4,06 |  |  |  |  |  |  |  |  |  |
17. Simaulium degrangei |  | 0,21 | 0,45 |  |  |  |  | 0,23 |  |  |  |  |  |  |  |
18. Simulivm morsitans |  | 2,71 |  | 0,23 |  |  | 0,21 |  |  | 0,62 |  |  |  |  |  |
19. Siaulium reptans | 1,7 | 13,46 | 9,2 | 17,8 | 3,03 | 2,83 | 0,21 | 3,15 | 7,65 | 22,98 |  |  |  | 25,19 |  | 46,8
20. Simulium colombaschenee | 3,39 | 1,36 | 0,45 |  | 9,9 |  |  | 0,23 | 4,92 | 4,35 |  |  |  |  |  |
21. Simulium voilense |  | 0,94 | 0,11 |  |  |  |  | 0,68 | 4,37 |  |  |  |  |  |  |