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Dragonflies, Sympetrum spp., are indispensable to agriculture and are a central element of culture in Japan. However, S. frequens populations in rice paddy fields have declined in recent decades. Dragonfly larvae are predatory aquatic insects that feed on other organisms found in habitats with slow-moving or standing water. The increasing use of fipronil and neonicotinoid insecticides in agriculture is also increasing exposure to Sympetrum spp. in larval stages through paddy soil and water. The role of fipronil insecticides in the decline of dragonflies is of concern, and we here examine the sublethal effects of this insecticide on the feeding behaviors of two Sympetrum spp. Based on the quantity of prey items consumed and the time to capture prey items, feeding inhibition was determined to be a potential mechanism of the decline of Sympetrum spp. following 48-h exposure to fipronil and fipronil sulfone. Prey consumption by S. infuscatum was significantly reduced for fipronil sulfone at all concentrations (0.01-1000 μg/L). S. frequens exposed to 1, 10, 100 and 1000 μg/L fipronil sulfone had significantly longer prey capture times. Fipronil sulfone was 2.8, 9.7 and 10.5 times more toxic to S. infuscatum than fipronil in terms of acute toxicity, feeding inhibition and delayed toxicity, respectively. In addition, fipronil sulfone was 6.6, 2.9 and 9.1 times more toxic, respectively, to S. frequens than fipronil. Our findings suggest that sublethal effects on feeding inhibition lead to severe mortality at realistic paddy soil and water concentrations. Our results provide the first demonstration that short-term exposure to fipronil and fipronil sulfone can consequently cause significant harm to dragonfly larvae survival due to feeding inhibition. These findings have implications for current pesticide risk assessment and dragonfly protection.

In South Korea, both Sympetrum depressiusculum Sélys, 1841 (Odonata: Libellulidae), which is distributed throughout Europe and from Russia to the Korean Peninsula, and Sympetrum frequens Sélys, 1883, which is endemic to Japan, are recorded. However, the identity of South Korean populations and the validity of listing the two species have not yet been settled. In this study, we collected seventy-four individuals of Sympetrum species from South Korea (five localities), Russia, The Netherlands, and Japan. These samples were examined for morphology and sequenced for partial COI, 16S rRNA, and a nuclear internal spacer (ITS) region, after which these molecular data were combined with available public data from Russia, Japan, and The Netherlands. Major morphological characters that have been used to distinguish the two species and phylogenetic, network, and structure analyses all consistently suggest that South Korean populations form a single species. Consequently, it could be valid to treat South Korean populations as one species, S. depressiusculum, by applying the senior name. Nevertheless, the validity of maintaining each as an independent species in other countries may need additional study considering that our samples were focused more on South Korea and limited for Europe, Russia, and Japan.

Aggregations of dragonflies engaging in copulation were observed in Sympetrum internum dragonflies and potentially other Sympetrum species. On four separate occasions in Colorado and Wyoming during the 2023 summer, Sympetrum species were found copulating in groups of three to >10 pairs at ponds located within the perimeters of recent wildfires. While post-copulatory aggregations have been described for Sympetrum species, aggregatory behavior during mating remains less well documented in any dragonfly species. Future research should explore the taxonomic prevalence of aggregate copulation in dragonflies and the ecological or social drivers that might favor or oppose its expression.

Odonata species can be used to indicate the effects of anthropogenic disturbance on agrobiodiversity. In Japan, populations of some odonate species inhabiting rice paddy fields have decreased strongly owing to their high susceptibility to insecticides, and they therefore need to be conserved. To identify effective conservation strategies, we investigated how agricultural practices (conventional vs. environmentally friendly: EF) and surrounding landscape (area of forest at three spatial scales, namely 50, 100 and 200 m from the edge of the paddy field) influenced the abundance of odonates in rice paddies in Tochigi Prefecture, Japan. Generalized linear mixed-effect models revealed that EF farming increased the abundance of odonate adults and the number of nymphal exuviae, suggesting a strong negative effect of insecticides. The influence of forest area at the local scale on the numbers of odonate adults and nymphal exuviae was small, with the exception of a strong negative influence on adult Sympetrum infuscatum: the presence of a large area of forest within 200 m of the edge of the paddy field reduced their abundance, probably reflecting this dragonfly’s oviposition site preference. Our results suggest that EF farming could generally support the conservation and recovery of local populations of odonates, but its effectiveness potentially varies depending on the ecological aspects of each species.

Neonicotinoids and fipronil are the most widely used insecticides in the world. Previous studies showed that these compounds have high toxicity to a wide taxonomic range of non-target invertebrates. In rice cultivation, they are frequently used for nursery-box treatment of rice seedlings. The use of fipronil and neonicotinoid imidacloprid is suspected to be the main cause of population declines of red dragonflies, in particular Sympetrum frequens , because they have high lethal toxicity to dragonfly nymphs and the timing of the insecticides’ introduction in Japan (i.e., the late 1990s) overlapped with the sharp population declines. However, a causal link between application of these insecticides and population declines of the dragonflies remains unclear. Therefore, we estimated the amount of the insecticides applied for nursery-box treatment of rice seedlings and analyzed currently available information to evaluate the causality between fipronil and imidacloprid usage and population decline of S . frequens using Hill’s causality criteria. Based on our scoring of Hill’s nine criteria, the strongest lines of evidence were strength, plausibility, and coherence, whereas the weakest were temporality and biological gradient. We conclude that the use of these insecticides, particularly fipronil, was a major cause of the declines of S . frequens in Japan in the 1990s, with a high degree of certainty. The existing information and our analyses, however, do not allow us to exclude the possibility that some agronomic practices (e.g., midsummer drainage or crop rotation) that can severely limit the survival of aquatic nymphs also played a role in the dragonfly’s decline.

Risk-spreading behaviour is often exhibited by animals as a response to unpredictably variable environments. Using field and laboratory studies, we tested the hypothesis that Sympetrum vicinum dragonflies spread the risks of winter environments by laying eggs across a terrestrial–aquatic gradient. Sympetrum vicinum eggs that overwintered in terrestrial and benthic-limnetic habitats had significantly higher hatching success compared with eggs that overwintered in littoral sites. Low success may have been caused by hypoxia due to excess sediment in the littoral samples in the lab. While hypoxia experienced under winter conditions (4°C) had no negative effect on hatching success, hatching in hypoxic and anoxic water significantly decreased hatching success. Opportunistic egg predation by a winter-active caddisfly significantly decreased egg hatching success. Because S. vicinum eggs have a relatively low supercooling point (− 26.25°C), freezing may not be a significant source of mortality in terrestrial or aquatic sites. By ovipositing in both terrestrial and aquatic environments, female dragonflies may be balancing the unpredictable risks of both the failure to inundate the eggs and egg predation. Our research highlights the potential for biotic interactions during winter to shape the behaviour and life-history of aquatic invertebrates.

Here, we investigate the evolutionary history of five northern dragonfly species to evaluate what role the last glaciation period may have played in their current distributions. We look at the population structure and estimate divergence times for populations of the following species: Aeshna juncea (Linnaeus), Aeshna subarctica Walker, Sympetrum danae (Sulzer), Libellula quadrimaculata Linnaeus and Somatochlora sahlbergi Trybom across their Holarctic range. Our results suggest a common phylogeographic pattern across all species except for S. sahlbergi . First, we find that North American and European populations are genetically distinct and have perhaps been separated for more than 400,000 years. Second, our data suggests that, based on genetics, populations from the Greater Beringian region (Beringia, Japan and China) have haplotypes that cluster with North America or Europe depending on the species rather than having a shared geographic affinity. This is perhaps a result of fluctuating sea levels and ice sheet coverage during the Quaternary period that influenced dispersal routes and refugia. Indeed, glacial Beringia may have been as much a transit zone as a refugia for dragonflies. Somatochlora sahlbergi shows no genetic variation across its range and therefore does not share the geographic patterns found in the other circumboreal dragonflies studied here. Lastly, we discuss the taxonomic status of Sympetrum danae , which our results indicate is a species complex comprising two species, one found in Eurasia through Beringia, and the other in North America east and south of Beringia. Through this study we present a shared history among different species from different families of dragonflies, which are influenced by the climatic fluctuations of the past.

Organic farming has potential for the conservation of global biodiversity and associated ecosystem services. Despite this, knowledge of the effects of organic farming systems on farmland biodiversity is limited in Asia, the worldwide leader in rice production. We conducted the first national‐scale study to investigate the effects of three different rice farming systems (conventional, low‐input and organic) and specific management practices (e.g. herbicide and insecticide applications, crop rotation and levee‐vegetation management) on species richness and abundance of multiple taxonomic groups (plants, invertebrates, Pelophylax and Hyla japonica frogs, cobitid loaches and birds) in Japan during 2013–2015. Organic fields supported the highest richness and abundance of several taxonomic groups (native/Red List plants, Tetragnatha spiders, Sympetrum dragonflies and Pelophylax frogs), followed by low‐input and conventional fields. We also found taxon‐specific responses to specific management practices. For instance, plant richness and Tetragnatha and Sympetrum abundance increased with reduced herbicide and/or insecticide applications. Sympetrum and cobitid loach abundance increased in the absence of crop rotation, whereas H. japonica abundance increased with crop rotation. Pelophylax abundance increased with an increased height of levee vegetation. At spatial scales larger than single fields, waterbird richness and abundance were positively correlated with the proportion of organic rice fields, presumably due to increased prey abundance. Meanwhile, landbird richness and abundance were positively associated with annual precipitation and annual mean temperature, suggesting that such climate increases food availability. Synthesis and applications. We highlight the positive effects of organic and low‐input farming for biodiversity relative to conventional farming in rice paddies. We also provide the scientific basis of the current agri‐environmental schemes in Japan, subsidising organic and low‐input farming for biodiversity. The taxon‐specific associations with management practices indicate that avoiding crop rotation, maintaining levee vegetation and organic farming at large spatial scales can also be wildlife friendly. These practices may thus be incorporated into agri‐environment schemes for effective biodiversity conservation. 要旨 有機農業は、生物多様性と、それに関連する生態系サービスの保全に重要な役割を果たすと考えられている。しかし、有機農業が農地の生物多様性にもたらす影響は十分にわかっておらず、特に水稲の主要な生産地であるアジアにおいて知見が非常に少ない。 私たちは、日本の水田では初となる全国規模の野外調査を2013–2015年に行い、慣行、減農薬および有機栽培の3つの農法の違い、および、除草剤・殺虫剤の施用、輪作の有無、畦畔の植生管理等の管理手法の違いが複数の生物種群（植物、無脊椎動物、トノサマガエル属、ニホンアマガエル、ドジョウ科および鳥類）に与える影響を評価した。 在来／レッドリスト植物種数、アシナガグモ属、アカネ属およびトノサマガエル属の個体数は有機栽培の水田で最も多く、次いで減農薬栽培田、慣行栽培田となった。また、管理手法の違いに対する応答は分類群毎に異なることが明らかとなった。具体的には、植物種数、およびアシナガグモ属とアカネ属の個体数は除草剤もしくは殺虫剤施用の少ない水田に多かった。アカネ属とドジョウ科の個体数は輪作を実施しない水田に多かったが、一方でニホンアマガエルの個体数は輪作を実施する水田に多かった。トノサマガエル属の個体数は畦畔の植生高に比例して増加した。 水田団地のスケールでみると、水鳥類の種数・個体数は有機栽培田の面積率と正の相関を示しており、これは食物量の増加によるものと考えられた。一方、陸鳥類の種数・個体数は年降水量および年平均気温と正に相関しており、こうした気候が食物量を増加させる結果と示唆された。 総括および応用　慣行栽培と比較して、有機栽培および減農薬栽培が農地の生物多様性に正の影響をもたらすことが明らかになった。これにより、現在、日本で実施される農業環境政策（有機・減農薬栽培等に対する交付金制度）の効果について科学的な評価基盤を提供することができた。さらに、輪作を回避すること、畦畔植生を適当な高さに維持すること、および有機栽培を行う水田を空間的にまとめることも、特定の分類群の保全に有効であることがわかり、こうした取組の推進が望まれる。 We highlight the positive effects of organic and low‐input farming for biodiversity relative to conventional farming in rice paddies. We also provide the scientific basis of the current agri‐environmental schemes in Japan, subsidising organic and low‐input farming for biodiversity. The taxon‐specific associations with management practices indicate that avoiding crop rotation, maintaining levee vegetation and organic farming at large spatial scales can also be wildlife friendly. These practices may thus be incorporated into agri‐environment schemes for effective biodiversity conservation.

For a vector species, understanding their egg raft predation (consumption) or destruction is essential for both ecological and human health reasons since it directly influences its fitness. In a mesocosm experiment, we assessed differences in Culiseta longiareolata egg raft predation/destruction by three aquatic predators Notonecta maculata (backswimmers), Sympetrum fonscolombii (dragonflies) and Ommatotriton vittatus (newts), both in the presence and absence of an alternate prey (Culex larve). Egg raft predation and destruction significantly differed between predators types, and strongly influenced by the presence of alternate prey. Backswimmers attacked and destroyed (broke down) all egg rafts until they disintegrated and sank in water regardless of whether an alternative prey was present. Egg raft predation by dragonflies was common in the absence of alternative prey, but rare when alternative prey was present. Predation by newts was rare regardless of whether there was an alternative prey. The number of alternate prey consumed also significantly differed between predators (P < 0.001) with backswimmers being the most effective predator. Relatively few studies have tested for egg raft predation/destruction. Hence it is crucial that we conduct similar trials in other landscapes since such predators can prove to be key agents for the biological control of mosquitoes.

Dragonfly wings resist millions of cycles of dynamic loading in their lifespan. During their operation, the wings are subjected to relatively high mechanical stresses. They further experience accidental collisions which result from the insects’ daily activities, such as foraging, mating and fighting with other individuals. All these factors may lead to irreversible wing damage. Here, for the first time, we collected qualitative and quantitative data to systematically investigate the occurrence of damage in dragonfly wings in nature. The results obtained from the analysis of 119 wings of more than 30 individuals of Sympetrum vulgatum (Anisoptera, Libellulidae), collected at the second half of their flight period, indicate a high risk of damage in both fore- and hindwings. Statistical analyses show no significant difference between the extents of damage neither in fore- and hindwings nor in male and female dragonflies. However, we observe a considerable difference in the probability of damage in different wing regions. The wing damage is found to be mainly due to two failure modes: wear and fracture.