Abstract: | The present work, dealing with benthic fauna of the Bistriþa River, was developed following some observations on trichoptera pupal and larval cases. It is well known the building instinct of these insects’ larvae. L. Botoºãneanu (1963) made a classification of all construction types of aquatic larvae of insects, separated in systematic groups from our country (also mentioning exotic species with special types of buildings). Some criteria of his classification are: the shape, the nature of building materials - organic (silk and other secretions, algae, vegetal detritus, leaves, wood, mollusk shells) or mineral (pebbles, sand), the mobility.
The exclusively mineral composition of some trichoptera larvae is already known (most Rhyacophilidae before pupation, Sericostomatidae, Glossossomatidae and other family's larvae), vegetal, or vegetal and mineral construction (most limnephilid larvae).
Most of caddisflies larvae keys, scientific articles describe the cases and some of their components in percentage without explanations on the origin or the method of obtaining these percentages. The characteristics of the larval or pupal case are still used to identify the family, genus even species (Tachet et all., 2000). Concerning particularly the species it is not anymore recommended as major criteria because the stressed larva (during the collection for example) which can live the case or, exceptionally, can use another species case after leaving its own (Wallace et all., 2003).
The main purpose of this study is to find out if some trichoptera larvae have any preference in choosing a construction material in natural conditions so we took a group of individuals large enough from a microhabitat. The microhabitat is described mainly by the substrate (Angelier, 2000). In our study the substrate was the area of the riverbed under a big rock from which we collected fixed pupa and last instar larval cases) of the species identified as Allogamus auricollis.
On the main course of Bistriþa River, in the area of Vatra Dornei, the ground grevel is constituted mainly from cristaline schists present in the riverbed and also eocene calcares - apported by some of the tributaries - but „diluted” in the cristaline in this sector (Donisã & Poghirc, 1968). |
