Seasonal occurrences, reproductive seasons, and habitat environments of an endangered damselfly Paracercion plagiosum (Odonata: Coenagrionidae) in ponds neighboring Lake Izunuma–Uchinuma, Japan

Abstract

We investigated the seasonal occurrences, reproductive seasons, and habitat environments of an endangered damselfly Paracercion plagiosum (Odonata: Coenagrionidae) in ponds neighboring Lake Izunuma–Uchinuma of the northern Miyagi Prefecture, Japan. P. plagiosum was observed from early June to mid-August in both ponds, with the peak of the adults observed in late June. Reproductive behavior (tandem linkage, mating, and egg-laying) was observed from late June to early August in both ponds, and the aquatic plant composition differed between the two ponds. Several species of emerged plants were observed at the water edge, and the floating-leaved plants Trapa spp. were observed on the water surface. However, the free-floating plant Utricularia australis was observed only in one of the targeted ponds. In the Pond A dominated by Trapa spp., all egg-laying of this species occurred in Trapa spp., but in the Pond B where Trapa spp. and U. australis coexisted, 70％ of egg-laying occurred in U. australis. This suggests that egg-laying on the U. australis may be a factor that increases the fitness of this species compared to Trapa spp. In Lake Izunuma–Uchinuma, Nelumbo nucifera and Trapa spp. have become dominant over a wide area of the lake due to eutrophication, and the environment in which U. australis grows has become precious. Environmental management of the ponds and restoration activity of lakeshore vegetation zone in Lake Izunuma–Uchinuma will be important for the conservation of this endangered species.