Sympetrum pedemontanum (Müller in Allioni) (Odonata: Libellulidae), which is distributed widely in the Eurasian continent and its neighboring islands, is listed as a Least Concern species in the International Union for Conservation of Nature Red List (2015). In Japan, however, the population of its subspecies S. pedemontanum elatum (Selys) has been rapidly decreasing since the 1970s. In order to conserve this subspecies, it is important to understand the seasonal microhabitat use by its larvae. However, this has been a difficult task because larvae of S. pedemontanum elatum often coexist with those of a common congener, S. eroticum (Selys), and cannot be morphologically distinguished from the latter. Thus, in this study, we first established a molecular technique based on the polymerase chain reaction to accurately identify each species. In the subsequent field survey in 2015 with its application in the Sakasegawa River, Hyogo Prefecture, we found that S. pedemontanum elatum larvae hatch in stagnant water and subsequently advance into weakly flowing water. Our results indicated a change in the microhabitats during the larval developmental process, reflecting the need for a continuous spectrum of stagnant, transitional, and flowing water. Such aquatic environments with a spectrum of water conditions are disappearing in Satoyama, a rural farming area in Japan. This has endangered species such as S. pedemontanum elatum and Oryzias latipes (Beloniformes: Adrianichthyidae) by depriving them of their favorable habitats. For their conservation, it is necessary to develop methods to recover the traditional aquatic environments in Satoyama.

Short and flat grass preferred by adults of the endangered dragonfly Sympetrum pedemontanum elatum (Odonata: Libellulidae

No abstract

Recent decreases in population size of some Sympetrum species (Odonata: Libellulidae) that used to flourish in paddy fields in Satoyama, Japan, are thought to be caused by the development of rice cropping systems. As habitat use is species-specific, some conservation studies have shown that the causes of the decline in darter populations may also be species-specific. While eggs and larvae of lentic species like Sympetrum frequens decrease owing to the effect of pesticides, those of S. pedemontanum elatum, which lives along weakly flowing water, are not influenced by these chemicals, although they have decreased with the modernization of water management in paddy fields. It is also known that drying of the soil surface in no-till farming areas does not reduce the population size of S. infuscatum, whose eggs have a higher resistance to drought than those of other darter species. For the conservation of darters, we should investigate habitat use during the developmental stages of each species, identify the causes of population decline, and maintain a suitable balance within the microhabitats required by each darter species. Such designed habitats will contribute to the conservation of not only darters, but also many other aquatic organisms endangered in the paddy fields of Satoyama.