矢作川水系および周辺河川におけるカワゲラ類（特にキカワゲラ属）の分布と生活史

Abstract

Stonefly nymphs (Insecta, Plecoptera) were collected at 80 sites in the Yahagi River system and in its surrounding rivers, central Honshu, Japan, in addition to our previous studies. The genera Kamimuria and Paragnetina were widely distributed in both upstream and downstream of the Yahagi Dam. Isoperla nipponica was widely distributed in upstream of the Yahagi Dam, but it tended to be few in downstream of the Yahagi Dam. The genus Xanthoneuria was widely distributed and abundant in upstream of the Yahagi Dam, but, in contrast, it was not collected at all in the main stem of the Yahagi River downstream of the Yahagi Dam (alt. 15-183 m, catchment area 513-1428 k㎡). In the surrounding areas of the Yahagi River system, Xanthoneuria nymphs were widely collected in the rivers of the Kiso River system and the Tenry? River system, although they were not collected in the rivers of the Toyo River system. In the Nagara River system, the nymphs were found in the rivers at altitudes of 64-104 m and with catchment areas of 278-1079k㎡. From these distribution patterns, it is considered that Xanthoneuria used to be distributed in the main stem of the Yahagi River below the Yahagi Dam, but the construction of the Dam would have changed the downstream environment and consequently Xanthoneuria has become uninhabitable there. By rearing of the nymphs, it was found that all three known species of Xanthoneuria from Japan, X. fulva, X. jouklii and X. bolivari inhabited the Yahagi River system. Xanthoneuria fulva tended to inhabit upper streams of the Yahagi River system, whereas X. jouklii tended to be collected in the rivers below the habitat of X. fulva, above the Yahagi Dam. X. bolivari was collected only in a tributary, the Ai River. The life cycle of X. jouklii was investigated at Sumigase (alt. 326 m). The eggs needed more than half a year to hatch. The change in size frequency of the nymphs indicates that the nymphs spent about one year underwater. Large nymphs of X. jouklii were collected from October through winter to May. The adults emerged simultaneously in late May. The life cycle of X. jouklii seems to be hemivoltine with very long hatching time. The life cycle of X. fulva was studied at Utsubo (alt. 980 m). The nymphs of X. fulva seems to need longer larval periods than those of X. jouklii, and the large nymphs were collected throughout the year.