Distribution Patterns and Habitat Characterization of Elmidae and Hydraenidae (Insecta: Coleoptera) in the Weidlingbach Near Vienna, Austria

Abstract

AbstractA total of 870 adult and 831 larval Elmidae and Hydraenidae were caught from September 1995 to September 1996 at the Weidlingbach, a fourth order tributary of the Danube near Vienna, Austria, using a Heß sampler at 14 sampling stations from source to mouth. Elmis maugetii (Latreille) and Riolus subviolaceus (Müller) accounted for 66.3% of the total, whereas Hydraena gracilis (Germar) was the most abundant Hydraenidae species.Based on head width, instars 1–6 were collected in E. maugetii, instars 2–6 in R. subviolaceus and instars 3–6 in Limnius volckmari (Panzer) and Riolus cupreus (Müller); from the remaining species, only instars 4–6 were sampled.E. maugetii was most abundant on coarse, moss‐covered substrates (median = 22.2 mm) exposed to high water velocity (median = 69.4 cm/s; range = 6.0–117.6 cm/s); the latter was also true for R. subviolaceus although it favoured smaller sediment grain sizes (median = 10.7 mm). Sites exposed to only moderate flow and with abundant filiform algae were preferred by Esolus parallelepipedus (Müller) and L. volckmari, whereas the Hydraenidae species, Esolus angustatus (Müller), R. cupreus and Oulimnius tuberculatus (Müller) were collected mostly at sites with moderate current speed and abundant moss‐covered pebbles of various size.Species richness and population density increased from source to mouth. At the spring sampling site Elmidae and Hydraenidae were completely lacking.