AQUATIC INSECT COMMUNITIES IN WINTER AND THE BIOTIC INDEX OF THE RIVERS WHICH FLOW INTO THE LAKE BIWA

Abstract

In the winter of 1964,the author studied on the aquatic insect communities of the lower parts of seven rivers flowing into Lake Biwa, and calculated the biotic index based on the BECK-TSUDA method. The author wishes here to report the results and to compare them with the data of the investigation of the summer of 1963. The results are summarized as follows : 1. The temperature of the river water in winter (at the time of the sampling) does not exceed 11℃ in the lower part of the seven rivers, while that in summer (at the time of the sampling) exceeded 20℃. The pH value was 7.0〜8.3. 2. In the seven rivers, the fauna of the aquatic insects differed between in winter and in summer. 3. Three rivers (Yogo River, Hino River and Ishida River) had richer standing crop of aquatic insects in winter than in summer. But in four rivers (Ado River, Chinai River, Okawa River and Ane River), the standing crop was nearly equal in both seasons. 4. In the seven rivers, the rate of the standing crop of each life form differed between in winter and in summer. 5. In the three rivers (Yogo River, Okawa River and Hino River), a higher biotic index was obtained in winter than in summer for various reasons.