Tagesperiodisches verhalten und habitatwechsel der larven von Potamophylax luctuosus (Trichoptera)

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Abstract
Larvae instars of Potamophylax luctuosus build their cases on different material and occur in different habitats. The distribution of the instars was observed in a brook and their daily pattern of locomotory activity was studied in the laboratory. 1. First instars build their cases of plant material. They prefer habitats well exposed to light and current and they are found especially on stones. They show no preference for either diurnal or nocturnal activity and no avoidence of light. 2. Later instars change from plant to stony cases. They are found chiefly in dim habitats, where current is slow. They gradually develop negative phototaxis and nocturnal activity. In constant conditions (DD) no endogenous rhythm has been observed. 3. Late instar larvae have stony cases of fairly uniform small stones. They chiefly are found beneath stones and roots in deep water. Their activity pattern is strictly nocturnal. In constant conditions (DD) they have an endogenous rhythm with a period of about 26–27 hrs. 4. The development of negative phototaxis and nocturnal activity is correlated with the demands of the young larvae for current and food. The endogenous rhythm of activity appears only in the latest instar, during which preparation for pupation occurs. Therefore, it appears that the endogenous rhythm is of great importance for the development of pupa and imago. 5. Daily activity patterns during life history of eight species of Trichoptera are compared.