THE RELATIONSHIP BETWEEN BLACKFLIES (DIPTERA: SIMULIIDAE) AND SOME HYDROCHEMICAL AND HYDROPHYSICAL PARAMETERS IN LARGE AND MEDIUM-SIZED LITHUANIAN RIVERS R. BERNOTIENE * Nature Research Centre, Vilnius, Lithuania ABSTRACT 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 permanganatic 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. Copyright © 2013 John Wiley & Sons, Ltd. key words: Simulium; density; communities; environmental variables; suspended matter Received 16 September 2011; Revised 31 August 2013; Accepted 11 October 2013 INTRODUCTION Blackflies (Diptera: Simuliidae) are small insects having a life cycle with aquatic preimaginal stages. Blackfly larvae are found in running water and are important components of stream communities (Carlsson, 1967), as a prey resource for predators (Gislason and Steingrimsson, 2004) and for their influence on particle dynamics (Malmqvist, 1994). Blackflies can aggregate at very high population densities at some river segments (Wotton, 1987), forming occasion- ally over 90% of the biomass of all water invertebrates (Niesolowski, 1980), so the annual number of bloodsucking blackflies that emerge from large rivers can be huge. In the adult stage, these insects are important and serious pests because of their painful bites, the enormous numbers involved in attacks and their ability to transmit diseases like onchocerciasis, anaplasmosis, tularemia and others (Budaeva and Khitsova, 2010). As filter feeders, blackfly larvae can be useful indicators of water quality (Rubtsov, 1978; Hilsenhoff, 1982), and they are used in the evaluation of some ecological indices in Europe (Skriver et al., 2000; Kownacki and Soszka, 2004). In spite of this, papers dealing with the abundance of the aquatic larval stages of blackflies are scarce (Niesolowski, 1980), and the factors that underlie the distri- bution of different blackfly species, especially in Europe, generally remain unknown. Those factors most often associ- ated with blackfly larval distribution are dissolved oxygen (Giller and Malmqvist, 1998), concentration of organic matter (Ali et al., 1974; Carlsson, 1967; Rubtsov, 1978), pH (Bernotiene, 2006b), ionic composition and water hard- ness (Kim and Merritt, 1988). The distribution of blackfly larvae is often also correlated with substrate type, velocity (Rubtsov, 1956; Lake and Burger, 1983; Bernotiene, 2006b) and depth (Adler and McCreadie, 1997). Possibly, the tie running water is for respiratory reasons or because the primary larval feeding mode, filtering, requires delivery of food (Adler et al., 2004). Filtering efficiency is influenced by factors such as temperature, current velocity, particle size and concentration or labral-fan morphology, which usually differ in different species (Adler et al., 2004). Dif- ferent blackfly species differ in their requirements, and these differences may contribute to differences in species *Correspondence to: R. Bernotiene, Nature Research Centre, Akademijos 2, Vilnius, Lithuania. E-mail: rasab@ekoi.lt RIVER RESEARCH AND APPLICATIONS River Res. Applic. 31: 728–735 (2015) Published online 8 November 2013 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/rra.2715 Copyright © 2013 John Wiley & Sons, Ltd.