Abstract We conducted an emergence survey of Isonychia (Isonychia) japonica Ulmer, 1919 and Isonychia (Prionoides) shima Matsumura, 1931 at four sites in the Izari-gawa River system, Hokkaido, Japan in 2015 and 2016 to investigate differences in emergence seasons between the species. The present study showed that I. (I.) japonica was widely distributed from up- to down-stream with abundant numbers in middle-stream, while I. (P.) shima was mostly distributed up-stream. The emergence season of I. (I.) japonica was longer than that of I. (P.) shima, but their emergence periods overlapped in August and early September, suggesting that their adults are not separated temporally. Body size comparison showed that, at the same sites, the emerged in August specimens of I. (I.) japonica were larger than those of I. (P.) shima.

中文翻译：

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Isonychia Eaton 两种蜉蝣的成虫出现模式和体型，1871 年来自日本北海道

摘要 我们于 2015 年和 2016 年在日本北海道伊泽里川水系的四个地点进行了 Isonychia (Isonychia) japonica Ulmer, 1919 和 Isonychia (Prionoides) shima Matsumura, 1931物种。目前的研究表明，粳稻从上游到下游分布广泛，中游数量较多，而粳稻主要分布在上游。I. (I.) japonica 的出苗季节比 I. (P.) shima 长，但它们的出苗时间在 8 月和 9 月初重叠，表明它们的成虫在时间上没有分开。体型比较表明，在同一地点，I. (I.) japonica 8 月份出现的标本比I. (P.) shima 大。