The roles of fallow‐field biotopes and winter‐flooded paddy fields as breeding and overwintering sites for aquatic insects

The populations of aquatic insects (Odonata, Hemiptera and Coleoptera) have substantially declined in paddy‐field environments, prompting efforts to conserve these species through creating fallow‐field biotopes and winter‐flooded paddies. However, permanent biotopes may not support the breeding of some species, and winter‐flooded paddies may be ineffective overwintering sites. As such, we assessed the roles of these habitats as breeding and overwintering sites through multiregional and two‐year single‐region surveys. We found that the biotopes served as breeding sites for Odonata and Hemiptera species that overwinter underwater, have long larval periods, or primarily inhabit ponds, as well as for endangered low‐mobility species (e.g., Ilybius apicalis ). Larvae of Dytiscidae (e.g., Graphoderus adamsii and Hydaticus bowringii ) and Hydrophilidae (e.g., Regimbartia attenuata ) and Sympetrum nymphs were more abundant in the paddy fields than in the biotopes during the breeding season. Similarly, prey abundance was higher and temporal overlap with prey was larger in paddy fields with dytiscid larvae, suggesting that aquatic insects select breeding sites based on prey availability and synchrony. Most aquatic insects were more abundant or were found in the biotopes in winter, indicating that winter‐flooded paddies are unsuitable overwintering sites. These findings highlight the complementary roles of biotopes and paddy fields in supporting aquatic insect diversity. The flooding of biotopes should be tailored to site conditions and target species to improve conservation outcomes.