ON THE DISTRIBUTION OF BLACK FLY LARVAE IN SMALL LOWLAND RIVERS IN LITHUANIA RASA BERNOTIENË Institute of Ecology of Vilnius University, LT – 08412 Vilnius, Lithuania ABSTRACT – It is known that the species composition of blackflies is different in different rivers. The aim of our study was to investigate peculiarities in the distribution of blackflies in small lowland rivers in Lithuania. The investigation was carried out at 15 study sites. In addition to blackfly larvae, physical and chemical indices of the rivers were also investigated. Our investigation revealed the presence of 15 species of blackflies, the dominant species differing from site to site. The results of multiple regression analysis showed that according to our data the larval density of five blackflies [Simulium trifasciatum Curtis, 1839; S. ornatum Meigen, 1818; S. lineatum (Meigen, 1804); S. morsitans Edwards, 1915; and S. rostratum Lundström, 1911] was statistically correlated with some physical parameters (substrate, discharge, water temperature) and chemical properties (water hardness, pH, permanganate oxidation of organic matter, quantity of nitrates and nitrites in the water) of the rivers. KEY WORDS: Simuliidae, lowland rivers, distribution, water parameters, Lithuania INTRODUCTION It is known that the species composition of blackflies is different in different rivers. Even closely situated rivers can be dominated by different blackfly species. For example, in the largest river of Lithuania, the Nemunas, Simulium maculatum (Meigen, 1804) and S. reptans (Linnaeus, 1758) larvae were dominant. A smaller tributary of the Nemunas River, the Merkys River, was characterized by dominance of S. equinum (Linnaeus, 1758), S. lineatum (Meigen, 1804), S. mor- sitans Edwards, 1915 and S. ornatum Meigen, 1818 (BERNOTIENE, 2006). The species composition of blackflies is often different even in rivers of similar size. What factors are important for the dis- tribution of preimaginal stages of one or another species of blackflies along rivers? Acta entomologica serbica, Supplement, 2006, 115-124 UDC 595.771 (474.5) : 574