Fish and macroinvertebrate assemblages reveal extensive degradation of the world's rivers.

Rivers suffer from multiple stressors acting simultaneously on their biota, but the consequences are poorly quantified at the global scale. We evaluated the biological condition of rivers globally, including the largest proportion of countries from the Global South published to date. We gathered macroinvertebrate- and fish-based assessments from 72,275 and 37,676 sites, respectively, from 64 study regions across six continents and 45 nations. Because assessments were based on differing methods, different systems were consolidated into a 3-class system: Good, Impaired, or Severely Impaired, following common guidelines. The proportion of sites in each class by study area was calculated and each region was assigned a Köppen-Geiger climate type, Human Footprint score (addressing landscape alterations), Human Development Index (HDI) score (addressing social welfare), % rivers with good ambient water quality, % protected freshwater key biodiversity areas; and % of forest area net change rate. We found that 50% of macroinvertebrate sites and 42% of fish sites were in Good condition, whereas 21% and 29% were Severely Impaired, respectively. The poorest biological conditions occurred in Arid and Equatorial climates and the best conditions occurred in Snow climates. Severely Impaired conditions were associated (Pearson correlation coefficient) with higher HDI scores, poorer physico-chemical water quality, and lower proportions of protected freshwater areas. Good biological conditions were associated with good water quality and increased forested areas. It is essential to implement statutory bioassessment programs in Asian, African, and South American countries, and continue them in Oceania, Europe, and North America. There is a need to invest in assessments based on fish, as there is less information globally and fish were strong indicators of degradation. Our study highlights a need to increase the extent and number of protected river catchments, preserve and restore natural forested areas in the catchments, treat wastewater discharges, and improve river connectivity.

Genome-wide molecular phylogenetic analyses and mating experiments which reveal the evolutionary history and an intermediate stage of speciation of a giant water bug.

The intermediate stages of speciation are important for understanding the processes involved in the creation of biodiversity, and also comprise a number of interesting phenomena. However, difficulties are associated with dividing clear speciation stages because speciation is a continuous process. Therefore, the elucidation of speciation is an interesting and important task in evolutionary biology. We herein present an example of a species in an intermediate stage of speciation using the giant water bug Appasus japonicus (Heteroptera, Belostomatidae) that was investigated using mating experiments and phylogenetic analyses of the mtDNA COI (658 bp) and 16S rRNA (435 bp) regions, and nDNA SSR (13 loci) and its genome-wide SNPs (11,241 SNPs). The results of our phylogenetic analyses based on their mtDNA data set and the genome-wide SNPs data set strongly supported the paraphyly of the Japanese populations. Therefore, it is suggested that their ancestral lineage which being distributed in the Japanese Archipelago subsequently migrated to the Eurasian Continent (i.e., back-dispersal occurred). Furthermore, the results of the mating experiments suggested that among A. japonicus, even between closely related lineages, premating reproductive isolation has been established by the differentiation of copulatory organ morphologies. In contrast, premating reproductive isolation is not established in the absence of the differentiation of copulatory organ morphologies, even if genetic differentiation is prominent. These results suggested that their phylogenetic distance does not predict premating reproductive isolation. Furthermore, in the present study, we present a clear example of premating reproductive isolation driving speciation between closely related lineages.

Description of two new species of Dicranomyia (Erostrata) crane fly (Diptera, Limoniidae) from Korea, with remarks on DNA barcoding and updated taxonomic key.

Two new crane fly species, Dicranomyia (Erostrata) jejuensissp. nov. and D. (E.) koreanasp. nov., from Korea are described on the basis of morphology and mitochondrial COI sequences. DNA barcode sequences for other four D. (Erostrata) species from Korea are also provided for the first time. The identification key for all known D. (Erostrata) species is presented.

Population genetic structure of a recent insect invasion: a gall midge, Asynapta groverae (Diptera: Cecidomyiidae) in South Korea since the first outbreak in 2008.

Outbreaks of Asynapta groverae, an invasive mycophagous gall midge, in South Korea have been repeatedly reported since the first occurrence in 2008. This species is a nuisance to residents owing to its mass emergence from newly built and furnished apartments. Here, the levels of genetic diversity, divergence, and structure of invasive A. groverae populations were investigated to understand their ability to survive in novel locations. Population genetic analyses were performed on seven invasive populations, including the first outbreak, sporadically emerged, and two laboratory-isolated (quarantined) populations, using the mitochondrial COI sequences and the ten novel microsatellite markers developed in this study. Non-indigenous A. groverae managed to maintain their populations for 12 years despite decreased genetic polymorphisms resulting from multiple incidences of founder effects by a small number of colonists. Additionally, the advantageous sustainability of A. groverae in the particle boards from which they emerge suggests that human-mediated dispersal is plausible, which may allow for the successful spread or invasion of A. groverae to new locations. This study is one of the few examples to demonstrate that an insect species successfully invaded new regions despite exhibiting decreased genetic diversity that was maintained for a decade. These findings indicate that the high genetic diversity of the initial founding population and asexual reproduction would contribute to the successful invasion of A. groverae in novel environments.

Diversity and DNA Barcode Analysis of Chironomids (Diptera: Chironomidae) from Large Rivers in South Korea.

Most large rivers in South Korea run through major cities, which often experience many environmental problems, including outbreaks of non-biting midges (Diptera: Chironomidae). However, chironomid species inhabiting large rivers have not been thoroughly investigated. We aimed to identify chironomid species collected from the four main large rivers in South Korea, construct a corresponding DNA barcode library, and examine the distribution and community structure of the identified riverine species. Adult chironomids were collected from nine sites along the rivers by using sweep nets and light traps during June and August 2015. Adults were morphologically identified, and COI nucleotide sequences were generated to verify the species identification and construct a DNA barcode library. The distribution and community structure of the identified species were also analyzed. A total of 124 COI sequences were established from 37 species belonging to 19 genera, and the resulting DNA barcode library effectively discriminated >90% of riverine Chironomidae in South Korea. Ten species, which are considered indicator species for large rivers, were collected from all four rivers. In addition, members of the subfamily Chironominae were collected more frequently than members of other subfamilies, with Tanytarsus tamagotoi being the most common and widespread chironomid species in South Korea. The DNA barcode library developed in this study will facilitate environmental studies of large rivers, such as biomonitoring chironomid larvae.

DNA Barcoding of Chironomid Larvae (Diptera: Chironomidae) from Large Rivers in South Korea to Facilitate Freshwater Biomonitoring and Public Health Surveillance.

Chironomid larvae are among the dominant benthic macroinvertebrates in all types of water systems in South Korea. They may pass through pipes in rivers (raw water) and occur in drinking water, thus creating public health issues. However, little is known about the larval stages of chironomids in large South Korean rivers. Therefore, we examined larval-adult associations in chironomids inhabiting major rivers used as water sources. The larvae were collected in 2015 and 2016 from nine locations along the four largest rivers in South Korea using a Ponar grab. Cytochrome oxidase subunit I (COI) sequences were generated from the larval specimens, and the species were identified by comparing these sequences to those in a newly constructed DNA barcode library of Chironomidae in South Korea. The samples from the four rivers yielded 61 mitochondrial COI sequences belonging to 18 species, including Hydrobaenus kondoi Saether, 1989, which was reported for the first time in the Korean Peninsula. Further, morphological identification of the larvae was conducted, and a pictorial taxonomic key to Chironomidae species in large rivers in South Korea was developed to facilitate freshwater biomonitoring research. Finally, an action flow chart was created for the rapid identification of chironomid larvae in infested drinking water or water purification facilities.

Invasion Pattern of Aedes aegypti in the Native Range of Ae. albopictus in Vietnam Revealed by Biogeographic and Population Genetic Analysis.

Since its introduction to Asia, Aedes aegypti has coexisted with the native species Ae. albopictus and has been reported to transmit several infectious diseases. However, the development of efficient disease prevention and vector control is hindered by the relatively poor understanding of the biogeography and the genetic diversity of Ae. aegypti in the region. This study aimed to determine the invasion patterns of Ae. aegypti by evaluating the distribution and abundance of Ae. aegypti and Ae. albopictus in different climatic regions (northern temperate and southern tropical regions) and habitats (domestic, peri-domestic, and natural). We further analyzed the genetic diversity and phylogenetic relationships of Ae. aegypti populations in Vietnam using mitochondrial COI gene sequences. Both Aedes species were observed at most of the study sites, but only Ae. albopictus thrived in northern mountainous areas. In sympatric ranges, the individual abundance of the species was influenced by regional climate and habitats. The tropical climate and availability of domestic containers facilitated the dominance of Ae. aegypti, whereas temperate climates and natural breeding sites facilitated that of Ae. albopictus. In addition, many genetic polymorphisms were detected in the Ae. aegypti populations, which formed two distinct genetic groups; however, this genetic diversity is unlikely to be relevant to the invasive success of Ae. aegypti. These findings provide insights into the mechanisms and patterns of Ae. Aegypti invasion, which depend on the climate and reproductive strategies in the native range of Ae. albopictus in Asia.

Role of the predaceous mosquito Toxorhynchites christophi (Diptera: Culicidae) in treehole ecosystems in a Korean forest.

Toxorhynchites mosquitoes have been studied as potential biological mosquito control agents because they consume other mosquito larvae. As a top predator, Toxorhynchites species are also considered keystone predators in phytotelmata. However, limited information is available regarding Toxorhynchites christophi, which is found in northeast Asia. The present study investigated whether Tx. christophi could reduce mosquito populations and increase species diversity by functioning as a mosquito control agent and keystone predator, respectively. During the study, aquatic insects were collected every three weeks (May-October, 2018) from tire habitats, which resemble treehole ecosystems, at the Korean National Arboretum in the central region of the Korean Peninsula. The samples were separated into the surface- and the substrate-groups based on their behavior, and the communities were compared based on the density of Tx. christophi. As a result, the communities with a higher density of the predators showed a higher diversity and evenness, and the communities also had a lower mosquito ratio, dominance, and density of the surface-group. The results of both non-metric multi-dimensional scaling and one-way analysis of similarities also indicated that the communities were affected by the density of Tx. christophi larvae. Similarity percentage analysis results revealed the effects of this predator on the communities could mainly be attributed to reductions in the densities of the three dominant mosquito species (Aedes koreicus, Ae. flavopictus, and Tripteroides bambusa). Thus, Tx. christophi may be valuable as both a biological mosquito control agent and keystone species of treehole ecosystems by reducing dominant mosquito species and improving species diversity.

Genetic Diversity and Population Structure of the Asian Tiger Mosquito (Aedes albopictus) in Vietnam: Evidence for Genetic Differentiation by Climate Region.

Aedes albopictus is a native mosquito to Southeast Asia with a high potential for disease transmission. Understanding how Ae. albopictus populations that develop in the species' native range is useful for planning future control strategies and for identifying the sources of invasive ranges. The present study aims to investigate the genetic diversity and population structure of Ae. albopictus across various climatic regions of Vietnam. We analyzed mitochondrial cytochrome oxidase I (COI) gene sequences from specimens collected from 16 localities, and we used distance-based redundancy analysis to evaluate the amount of variation in the genetic distance that could be explained by both geographic distance and climatic factors. High levels of genetic polymorphism were detected, and the haplotypes were similar to those sequences from both temperate and tropical regions worldwide. Of note, these haplotype groups were geographically distributed, resulting in a distinct population structure in which northeastern populations and the remaining populations were genetically differentiated. Notably, genetic variation among the Ae. albopictus populations was driven primarily by climatic factors (64.55%) and to a lesser extent was also influenced by geographic distance (33.73%). These findings fill important gaps in the current understanding of the population genetics of Ae. albopictus in Vietnam, especially with respect to providing data to track the origin of the invaded regions worldwide.

Predator selection and predator-prey interactions for the biological control of mosquito dengue vectors in northern Vietnam.

Predators and their interactions with target prey influence the efficiency of control strategies. In the present study, we demonstrate the implementation of natural predator selection for controlling dengue vectors in northern Vietnam through field-based observation of aquatic insect predators in natural habitats and lab-based assessment of predatorial capacities for several aquatic insect predators. The selected species was then used to evaluate the predatory-prey interaction using functional responses (FRs) toward 3rd- and 4th-instar larvae of four major medical mosquito species (Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, and Anopheles minimus). The preference of selected predators for Ae. aegypti larvae over other mosquito larvae was also investigated. Both field observation and lab experiments indicated that the giant water bug Diplonychus rusticus was abundant and exhibited the highest predatory capacity for mosquito larvae. The predator exhibited type II FRs when offered each of the four prey species, and the greatest attack rates were observed for Ae. aegypti and Ae. albopictus, with only negligible differences observed in the handling times of the prey species. Further, Manly's selectivity (α) values calculated from the prey choice experiments showed that Ae. aegypti was preferred over both Cx. quinquefasciatus and An. minimus. Together, these findings indicate that D. rusticus could be successfully used to facilitate the biological control of both Ae. aegypti and Ae. albopictus within the species' distributional overlap in Southeast Asia.

Phylogeographic Investigation of an Endangered Longhorn Beetle, Callipogon relictus (Coleoptera: Cerambycidae), in Northeast Asia: Implications for Future Restoration in Korea.

The longhorn beetle, Callipogon (Eoxenus) relictus Semenov, is the only remnant species found in the Palearctic region, while all other Callipogon species are distributed mainly in Central America and partly in South America. This species has been placed in the first category (as 'critically endangered') of the Red Data Book in Russia and designated as one of the top-priority target species among all endangered invertebrate species for restoration in South Korea since 2006. Although its restricted distribution in Northeast Asia with a high conservational value has been highlighted, genetic features of C. relictus from different geographic regions remain unexplored. We first investigated the level of genetic diversity and phylogeographic patterns of C. relictus to evaluate the current conservational status and the feasibility of the implementation of a restoration program. The average genetic divergence of mitochondrial gene COI based on Kimura-2-parameter distance among the four regions in Russia, China, North Korea, and South Korea was 2.2%, which lies within the range of intraspecific levels. However, two separate clades with 3.8% divergence were identified, despite no geographical clustering of haplotypes. The linear pattern of the haplotype network with a high level of haplotype and nucleotide diversities suggests that the wide range of currently fragmented populations might be the remnant of genetically diverse populations in the past. This study will provide crucial information on the genetic characteristics and phylogeographic history of C. relictus, which will help to establish conservation strategies for this cherished insect species in Northeast Asia.

A new species of Ephoron Williamson, 1802 (Ephemeroptera: Polymitarcyidae) from Thailand.

The genus Ephoron Williamson, 1802 is widely distributed around the world. In Thailand, only Ephoron indicus Pictet, 1843 was reported in 1961. In this study, a new Ephoron mayfly is described as Ephoron ookaewae sp. nov. In this new species description, the morphological characteristics of larvae and eggs in addition to adults are also shown in detail. Number of tubercles on mandibular tusks, and a median frontal process in larvae, distinguish Ephoron ookaewae sp. nov. from other Ephoron species. Their polar cap shape and a concave indentation in their eggs are also unusual. In addition, the mitochondrial DNA COI sequence data of the newly described Ephoron ookaewae sp. nov. is registered in GenBank. Registration of sequence data for the DNA barcode region of Ephoron mayflies inhabiting the Oriental region remains limited, however it will be useful for future research.

Process-based modeling to assess the nutrient removal efficiency of two endangered hydrophytes: Linking nutrient-cycle with a multiple-quotas approach.

Hydrophytes have been widely used to reduce nutrient levels in aquatic ecosystems, but only limited species with high nutrient removal efficiencies have been implemented. Thus, it is necessary to continually explore new candidate species with high nutrient removal efficiencies. To effectively explore the nutrient removal ability of hydrophytes, a new process-based model combining the multiple-quotas approach and nutrient-cycle model was developed. The multiple-quotas approach provides a theoretical framework to conceptually explain the uptake and response of autotrophs to multiple nutrients. The developed process-based model was validated using observational data from microcosm experiments with two emergent hydrophytes, Menyanthes trifoliata and Cicuta virosa. The results showed that both M. trifoliata and C. virosa effectively reduced nitrogen (N) and phosphorus (P) in both water and sediment layers, but M. trifoliata showed a higher removal efficiency for both nutrients than C. virosa, particularly for total ammonia + ammonium-nitrogen (NHx-N) and nitrate-nitrogen (NO3-N) in the sediment layer (M. trifoliata: 0.579-0.976 for NHx-N, 0.567-0.702 for NO3-N; C. virosa: 0.212-0.501 for NHx-N, 0.466-0.560 for NO3-N). In addition, M. trifoliata achieved the maximum removal efficiency for N and P at higher nutrient exposure levels than C. virosa (M. trifoliata: exposure level of 0.725-0.775; C. virosa: exposure level of 0.550-0.575). The developed model well simulated the species-specific growth patterns of hydrophytes depending on the nutrient exposure level as well as the N and P dynamics in the water and sediment layers. The approach adopted in this study provides a useful tool for discovering candidate species to improve hydrophyte diversity and effectively remove nutrients from aquatic ecosystems.

A New Fissiparous Brittle Star, Ophiacantha scissionis sp. nov. (Echinodermata, Ophiuroidea, Ophiacanthida), from Jeju Island, Korea.

A new species of Ophiuroidea, Ophiacantha scissionis sp. nov., is described. It was collected from Munseom Island, Jeju-do, South Korea at a depth of 28-36 m, by SCUBA diving. Ophiacantha scissionis has unique and distinct morphological characteristics: small disk, densely covered by small trifid spines, radial shields completely concealed by disk spines, six arms with four arm spines proximally, fissiparous. In addition, this species is clearly distinguished from other species of Ophiacantha by mitochondrial COI. This species is usually hexamerous and reproduces asexually by fissiparity. It is the first report of fissiparous reproduction in the genus Ophiacantha.

Relationships between predatory aquatic insects and mosquito larvae in residential areas in northern Thailand.

In order to elucidate the poorly understood relationships between mosquito larvae and their predatory aquatic insects in urban and suburban areas of tropical Southeast Asia, where vector-borne diseases are prevalent, aquatic insects were sampled from 14 aquatic habitats in residential areas of Chiang Mai, northern Thailand, during the rainy season (July to November) in 2016. Correlations among biological variables, densities of major predatory aquatic insect groups (i.e., Odonata, Coleoptera, and Hemiptera: OCH group) in wetlands and artificial lentic habitats, and the density of mosquito larvae were analyzed. Among the sampled mosquito larvae, Culex spp. were the most abundant, and both OCH density and water quality were major determinants of Culex spp. density (rs = -0.302 and -0.396, respectively). Logistic regression analyses indicated that the probability of Culex spp. occurrence was significantly and negatively correlated with OCH density. Furthermore, high macrophyte abundance was associated with higher predator density, potentially reducing mosquito density. Hemipteran predators were most negatively correlated with Culex spp. density, regardless of whether macrophyte abundance was high or low (rs = -0.547 and -0.533, respectively). Therefore, hemipteran predators were the most important aquatic insect predators in the urban and suburban residential areas of Chiang Mai, Thailand, and OCH species, such as the hemipteran Micronecta scutellaris, could be used as biological control agents against mosquitoes in the region.

Forecasting Spring Flight of Ips subelongatus (Coleoptera: Curculionidae: Scolytinae) in Japanese larch Larix kaempferi (Pinales: Pinaceae) Forests in the Republic of Korea.

Ips subelongatus is a species of bark beetle experiencing population outbreaks in Korea. In this study, a predictive model and empirical prediction were used to forecast the spring flight of these beetles in Japanese larch forests. The number of beetles caught in pheromone traps was investigated in larch forests thinned in 2009, 2010, 2012, or 2013. Data from the sites thinned in 2009, 2010, or 2012 were used in the predictive model based on a degree-day model that was validated using data from the site thinned in 2013. The lower threshold temperature for flight (LTF) and a thermal sum for the spring flight of I. subelongatus were estimated. The empirical prediction that beetles initiate their flight when daily maximum temperatures reach 16 or 20°C was tested using daily maximum temperature and the beetles caught. The LTF was estimated as 5.97°C, with 42.95 degree-days required for initiation of spring flight. The median flight dates were estimated with a discrepancy from 1 to 3 d by the predictive model. Using the empirical prediction, differences between the day when daily maximum temperature reached 16 or 20°C and flight peak days ranged from 4 to 45 d. These results demonstrate that the predictive model is more suitable than the empirical prediction for predicting the spring flight of I. subelongatus. Overwintering I. subelongatus adults seem to need to gain a determined thermal sum before initiating spring flight rather than merely waiting for the daily maximum temperature to exceed a critical temperature.

Estimating Flight Distance of Platypus koryoensis (Coleoptera: Curculionidae) by Mark-Release-Recapture and Its Validation by Field Observation.

Korean oak wilt (KOW) is vectored by the beetle Platypus koryoensis (Murayama) (Coleoptera: Curculionidae), a native species of Korea, whose dispersal distance is a key factor determining the spread of damage by KOW. To estimate dispersal distance at stand level, we conducted a mark-release-recapture (MRR) experiment and validated its results using an independent data. Sticky traps were attached to the trunks of oak trees up to 48.8 m from the release point. Beetles were marked with different three fluorescent powders by date and released, and the number of recaptured beetles was counted 90 min after release. To validate the flight distance, annual mean dispersal distance of P. koryoensis population was analyzed using GPS coordinates of oak trees with the symptom of KOW recorded in the field from 2012 to 2014 in independent oak stands that have been damaged by KOW since 2012. The beetles were recaptured only on the day they were released, suggesting that the beetles only make one flight. The percentage of recaptured beetles was 6.0 ± 1.6%. The mean dispersal distance was 18.0 ± 1.3 m, and more than 85% of recaptured beetles were caught within 25 m. Annual movement distances in infested stands were 24.1 and 19.9 m from 2012 to 2013 and 2013 to 2014, respectively, similar to the dispersal distance obtained from our MRR experiment. Our results showed that the dispersal distance of P. koryoensis estimated by MRR is a useful process for predicting the spread of areas damaged by KOW.

Loboplusia coreana sp. nov. from South Korea, only the second species of a genus originally described from Costa Rica (Diptera: Cecidomyiidae, Winnertziinae).

The genus Loboplusia was recently introduced for a remarkable species of Diallactiini from the cloud forest of Costa Rica (Jaschhof 2016). Males of that species, Loboplusia zurqui Jaschhof, 2016, were found to differ fundamentally from other Diallactiini, with the following traits defining the genus. The scutum is provided with a bright membranous patch called the prescutellar window; setae on the legs, especially the tarsi, are fringed; the gonostylus consists of two lobes (not a single lobe as is the basic pattern in Diallactiini); and the bridge connecting the gonocoxites ventrobasally is markedly shortened (Jaschhof 2016: fig. 15). A diallactiine collected recently by one of us (YJB) in South Korea shows exactly the same characters and is no doubt congeneric with L. zurqui. At the same time there are clear distinctions in the genitalia indicating that the South Korean species is discrete, so it is described and named here L. coreana Jaschhof Ham sp. nov. With a single species each in Central America and Eastern Asia, the genus Loboplusia has a distinctly odd distribution, a circumstance that is briefly discussed.

Distribution of the longhorned beetle Callipogon relictus (Coleoptera: Cerambycidae) in Northeast Asia.

The distribution of the longhorned beetle Callipogon (Eoxenus) relictus Semenov, 1899 (Coleoptera: Cerambycidae) in Northeast Asia was summarized for the first time, based on the examination of comprehensive material. Callipogon relictus is the only representative of the genus Callipogon in the Palearctic region. Its distribution ranges from Shanxi province (China) in the south, northward through the Korean Peninsula to Amur Oblast (Russia), and from Inner Mongolia (China) in the west to the coastal area of the Russian Far East.

The bipartite mitochondrial genome of Ruizia karukerae (Rhigonematomorpha, Nematoda).

Mitochondrial genes and whole mitochondrial genome sequences are widely used as molecular markers in studying population genetics and resolving both deep and shallow nodes in phylogenetics. In animals the mitochondrial genome is generally composed of a single chromosome, but mystifying exceptions sometimes occur. We determined the complete mitochondrial genome of the millipede-parasitic nematode Ruizia karukerae and found its mitochondrial genome consists of two circular chromosomes, which is highly unusual in bilateral animals. Chromosome I is 7,659 bp and includes six protein-coding genes, two rRNA genes and nine tRNA genes. Chromosome II comprises 7,647 bp, with seven protein-coding genes and 16 tRNA genes. Interestingly, both chromosomes share a 1,010 bp sequence containing duplicate copies of cox2 and three tRNA genes (trnD, trnG and trnH), and the nucleotide sequences between the duplicated homologous gene copies are nearly identical, suggesting a possible recent genesis for this bipartite mitochondrial genome. Given that little is known about the formation, maintenance or evolution of abnormal mitochondrial genome structures, R. karukerae mtDNA may provide an important early glimpse into this process.