THE RELATIONSHIP BETWEEN BLACKFLIES (DIPTERA: SIMULIIDAE) AND SOME HYDROCHEMICAL AND HYDROPHYSICAL PARAMETERS IN LARGE AND MEDIUM-SIZED LITHUANIAN RIVERS

摘要

Blackfly larvae are known as indicators of physical and chemical conditions in rivers, and the adults may be harmful for humans and cattle. In order to obtain more insight into the environmental variables governing the distribution of various blackfly species, a survey was conducted in 2000-2004 in the Nemunas River (Lithuania) and in its four major tributaries. The total density of blackfly larvae, the density of each species, hydrochemical parameters (concentrations of dissolved oxygen, total nitrogen and phosphorus, pH, concentration of suspended matter and pennanganatic oxidation of organic matter) and hydrophysical parameters (current velocity, discharge and water temperature) were recorded. The total density of blackfly larvae was significantly positively correlated with the concentration of suspended matter at the respective study sites. The concentration of suspended matter and the permanganatic oxidation of organic matter were positively associated with the densities of Simulium maculatum, Simulium reptans and Simulium erythrocephalum and negatively with the densities of Simulium equinum and the Simulium ornatum group. Water temperature had a positive influence on the density of S. erythrocephalum and a negative influence on the density of S. equinum larvae. The density of Simulium lineatum was positively associated with the concentration of total nitrogen, and the density of Simulium morsitans was positively associated with the current velocity. Redundancy analysis have proven these associations. The analysis of the relationships between the densities of seven blackfly species and nine environmental variables in large and medium-sized rivers in Lithuania revealed that parameters related to organic pollution had an influence on the densities of most of investigated species.