びわ湖の蜻蛉類の生態と分布

抄録

The present paper deals with the ecological studies of the dragonflies of Lake Biwa, from 1962 to 1963. As the larvae of many dragonflies emerge in spring and summer, the exuviae were collected in those seasons. In autumn and winter, the dragnet was used for the collection of the larvae. Sampling stations are shown in Figs 1,2. 1. About 16 species of dragonflies were found in this lake, and Gomphus was most abundant. 2. In summer the exuviae of Gomphus oculatus and G. annulatus were most abundant, followed by those of Epophthalmia elegans and Ictinogomphus clavaius in this order. The percentage of the exuviae collected at all the surveyed stations is as follows : G. oculatus 56 per cent, G. annulatus 18 per cent, Ictinogomphus clavatus 14 per cent, Epophthalmia elegans 6 per cent. The distribution of G. oculatus and G. annulatus is shown in Fig. 3. At the shore where the littoral region is large, the number of exuviae is large and where the littoral region is small, the number of exuviae is small. 3. Many of the 12 species of dragonflies found in the south basin of the lake, were mostly lenitic species. The exuviae were few along the Seta River. Sampling stations and distributions of the exuviae are ahown in Fig. 4. 4. In autumn in the case of Ictinogomphus clavatus and Epophthalmia elegans, mostly the larvae of the final stage were found. In the case of G. oculatus, the N-1 stage and N-4 stage were found. (The larvae of far younger stage are supposed to exist, but the mesh of the dragnet was too large to catch them.)