Effect of environmental factors on the abundance of riffle beetles (Coleoptera: Elmidae) and co-inhabiting aquatic insects within a reach scale, in Japan

Abstract

Riffle beetles (Coleoptera: Elmidae) are freshwater insects, and both adult and larval stages primarily inhabit running water. Therefore, environmental factors such as current velocity and substrate characteristics are crucial for the habitat of elmid beetles. The effects of substrate size structure, water depth, current velocity, and distance from terrestrial areas were evaluated for the adult and larval abundance of three common riffle beetles, Stenelmis nipponica Nomura, Zaitzevia awana (Kono), and Zaitzeviaria brevis (Nomura), and other cohabiting aquatic insects in a middle reach of the Mukogawa River, western Japan. The substrate size structure was summarized using principal component analysis, and the effects of environmental factors were analyzed using best subsets multiple regression. In summer (August), the three elmid species tended to be more abundant in the shallow quadrats of coarse-grained substrates, and substrate preference differed among species and stages. Current velocity and proximity to the terrestrial area were not significant for S. nipponica and Z. brevis, whereas adult Z. awana preferred faster-flowing currents and needed to the distance from the terrestrial areas. In winter (December), only the substrate size structure affected the abundance of adult elmid beetles. Although elmid beetles require highly sensitive habitats, they are easily surveyed. Therefore, they are convenient indicators of riverbed environments.

Implications for insect conservation

Preference of substrate sand size as their habitat differ among stages and seasons. Diverse substrate condition would be needed to conserve elmid beetles.