We studied the life cycle of the riffle beetle Leptelmis gracilis Sharp, 1888 from a population located in a river stream with lotic environments. Samples were collected monthly, between September 2018 and August 2019, from a tributary of the Hiikawa River in Izumo city, Shimane Prefecture, Honshu, Japan. Larvae were separated into five distinct groups based on size. The first and last instar larval sizes were identified through rearing methods. From these results, we determined that the larval stage of this species consists of five instars. From the monthly evaluations, the number of individuals corresponding to each instar period suggested that last‐instar larvae were dominant in May and that new adults emerged from July to August. Landing and pupation were estimated to occur from May to June. Monthly observations revealed that mature eggs were present in the female abdomen from April to June, as well as from August to September. It is, therefore, predicted that overwintering adults mainly oviposit from spring to early summer, while new adults oviposit from late summer to early autumn.

中文翻译：

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日本岛根县比伊川河系濒危浅滩甲虫 Leptelmis gracilis Sharp（鞘翅目：Elmidae）的生命周期

我们研究了浅滩甲虫 Leptelmis gracilis Sharp，1888 年来自位于具有激流环境的河流中的种群的生命周期。2018 年 9 月至 2019 年 8 月期间，每月从日本本州岛根县出云市比伊川河的一条支流收集样本。幼虫根据大小分为五个不同的组。通过饲养方法确定首龄和末龄幼虫的大小。根据这些结果，我们确定该物种的幼虫阶段由五个龄期组成。从每月的评估来看，每个龄期对应的个体数量表明，末龄幼虫在 5 月占优势，新成虫在 7 月至 8 月出现。着陆和化蛹估计发生在 5 月至 6 月。每月观察显示，4 月至 6 月以及 8 月至 9 月，雌性腹部存在成熟的卵。因此，预测越冬成虫主要在春季至初夏排卵，而新成虫则在夏末至初秋排卵。