Seasonal occurrence and habitat of Helophorus auriculatus Sharp, 1884, in a riparian area in Tochigi Prefecture, Japan

Abstract

A new locality of Helophorus auriculatus Sharp, 1884 was recorded in Tochigi Prefecture, which is the northern limit of this species in Japan. In this study area, this species was observed in small ponds, puddles, and slow-flowing pools scattered along riverbeds, where the water temperature was consistently below 20°C even in summer owing to spring water. Some diving and water scavenger beetles that inhabit the middle of the stream, were consistently observed along with this species. Helophorus auriculatus adults emerged in February, April, May, October, and December and disappeared during the summer; individuals collected in October were confirmed to be mating, and those collected in December laid eggs. The annual life history of H. auriculatus was similar to that of this species in Ibaraki Prefecture, but the peak of adult emergence occurred slightly later in this study area.