Exaptation of I4760M mutation in ryanodine receptor of Spodoptera exigua (Lepidoptera: Noctuidae): Lessons from museum and field samples.

Since 2007, diamide insecticides have been widely used in Korea to control various types of lepidopteran pests including Spodoptera exigua. For nearly a decade, diamide resistance in field populations of S. exigua across 18 localities has been monitored using bioassays. Despite their short history of use, resistance to diamide insecticides has emerged. Based on the LC50 values, some field populations showed a higher level of resistance to chlorantraniliprole, a diamide insecticide, compared to that of the susceptible strain, although regional and temporal variations were observed. To investigate resistance at a molecular level, we examined three mutations (Y4701C, I4790M, and G4946E) in the ryanodine receptor (RyR), which is the primary mechanism underlying diamide insecticide resistance. DNA sequencing showed that only the I4790M mutation was found in most field populations. As resistance levels varied significantly despite the uniform presence of the I4790M mutation, we considered the presence of another resistance factor. Further, the I4790M mutation was also found in S. exigua specimens collected prior to the commercialization of diamide insecticides in Korea as well as in other countries, such as the USA. This finding led us to hypothesize that the I4790M mutation were predisposed in field populations owing to selection factors other than diamide use. For further clarification, we conducted whole-genome sequencing of S. exigua (449.83 Mb) and re-sequencing of 18 individual whole genomes. However, no additional non-synonymous mutations were detected in the RyR-coding region. Therefore, we concluded that the high level of diamide insecticide resistance in Korean S. exigua is not caused by mutations at the target site, RyR, but is attributed to other factors that need to be investigated in future studies.

Spodoptera frugiperda (Lepidoptera: Noctuidae) Life Table Comparisons and Gut Microbiome Analysis Reared on Corn Varieties.

The fall armyworm (Spodoptera frugiperda, FAW) is an invasive migratory pest that has recently spread to Korea, damaging several corn cultivars with significant economic value. Comparisons of the growth stages of FAW were conducted based on the preferred feed. Therefore, we selected six maize cultivars, including three categories: (i) commercial waxy corn (mibaek 2-ho, heukjeom 2-ho, dreamoak); (ii) popcorn (oryun popcorn, oryun 2-ho); and (iii) processing corn (miheukchal). A significant effect was observed during the larvae period, pupal period, egg hatching ratio, and larvae weight, whereas the total survival period and adult period did not show significant variation among the tested corn cultivars. We identified variations in the FAW gut bacterial community that were dependent on the genotype of the corn maize feed. The identified phyla included Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. Among these genera, the most abundant bacterial genus was Enterococcus, followed by Ureibacillus. Enterococcus mundtii was the most abundant among the top 40 bacterial species. The intergenic PCR-based amplification and gene sequence of the colony isolates were also matched to the GenBank owing to the prevalence of E. mundtii. These results showed that the bacterial diversity and abundance of particular bacteria in the guts of FAWs were influenced by the six major maize corn cultivars.

Genetic Diversity of Dengue Vector Aedes albopictus Collected from South Korea, Japan, and Laos.

Aedes albopictus is native to Southeast Asia and has emerged as a major vector for vector-borne diseases that are spreading rapidly worldwide. Recent studies have shown that Ae. albopictus populations have different genetic groups dependent on their thermal adaptations; however, studies on Korean populations are limited. In this study, we analyzed the genetic diversity and structure of two mitochondrial genes (COI and ND5) and sixteen microsatellites in mosquitoes inhabiting Korea, Japan, and Laos. The results indicate that the Korean population has low genetic diversity, with an independent cluster distinct from the Laos population. Mixed clusters have also been observed in the Korean population. On the basis of these findings, two hypotheses are proposed. First, certain Korean populations are native. Second, some subpopulations that descended from the metapopulation (East Asian countries) were introduced to Japan before migrating to Korea. Furthermore, we previously demonstrated that Ae. albopictus appears to have been imported to Korea. In conclusion, the dengue-virus-carrying mosquitoes could migrate to Korea from Southeast Asian epidemic regions, where they can survive during the severe winter months. The key findings can be used to establish an integrated pest management strategy based on population genetics for the Korean Ae. albopictus population.

Genomic Shifts, Phenotypic Clines, and Fitness Costs Associated With Cold Tolerance in the Asian Tiger Mosquito.

Climatic variation is a key driver of genetic differentiation and phenotypic traits evolution, and local adaptation to temperature is expected in widespread species. We investigated phenotypic and genomic changes in the native range of the Asian tiger mosquito, Aedes albopictus. We first refine the phylogeographic structure based on genome-wide regions (1,901 double-digest restriction-site associated DNA single nucleotide polymophisms [ddRAD SNPs]) from 41 populations. We then explore the patterns of cold adaptation using phenotypic traits measured in common garden (wing size and cold tolerance) and genotype-temperature associations at targeted candidate regions (51,706 exon-capture SNPs) from nine populations. We confirm the existence of three evolutionary lineages including clades A (Malaysia, Thailand, Cambodia, and Laos), B (China and Okinawa), and C (South Korea and Japan). We identified temperature-associated differentiation in 15 out of 221 candidate regions but none in ddRAD regions, supporting the role of directional selection in detected genes. These include genes involved in lipid metabolism and a circadian clock gene. Most outlier SNPs are differently fixed between clades A and C, whereas clade B has an intermediate pattern. Females are larger at higher latitude yet produce no more eggs, which might favor the storage of energetic reserves in colder climate. Nondiapausing eggs from temperate populations survive better to cold exposure than those from tropical populations, suggesting they are protected from freezing damages but this cold tolerance has a fitness cost in terms of egg viability. Altogether, our results provide strong evidence for the thermal adaptation of A. albopictus across its wide temperature range.

Comparative population genetics of the invasive mosquito Aedes albopictus and the native mosquito Aedes flavopictus in the Korean peninsula.

BACKGROUND: Aedes mosquitoes are important invasive species contributing to the spread of chikungunya, dengue fever, yellow fever, zika virus, and other dangerous vector-borne diseases. Aedes albopictus is native to southeast Asia, with rapid expansion due to human activity, showing a wide distribution in the Korean peninsula. Aedes flavopictus is considered to be native to East Asia, with a broad distribution in the region, including the Korean peninsula. A better understanding of the genetic diversity of these species is critical for establishing strategies for disease prevention and vector control. METHODS: We obtained DNA from 148 specimens of Ae. albopictus and 166 specimens of Ae. flavopictus in Korea, and amplified two mitochondrial genes (COI and ND5) to compare the genetic diversity and structure of the two species. RESULTS: We obtained a 658-bp sequence of COI and a 423-bp sequence of ND5 from both mosquito species. We found low diversity and a nonsignificant population genetic structure in Ae. albopictus, and high diversity and a nonsignificant structure in Ae. flavopictus for these two mitochondrial genes. Aedes albopictus had fewer haplotypes with respect to the number of individuals, and a slight mismatch distribution was confirmed. By contrast, Ae. flavopictus had a large number of haplotypes compared with the number of individuals, and a large unimodal-type mismatch distribution was confirmed. Although the genetic structure of both species was nonsignificant, Ae. flavopictus exhibited higher genetic diversity than Ae. albopictus. CONCLUSIONS: Aedes albopictus appears to be an introduced species, whereas Ae. flavopictus is endemic to the Korean peninsula, and the difference in genetic diversity between the two species is related to their adaptability and introduction history. Further studies on the genetic structure and diversity of these mosquitos will provide useful data for vector control.

Complete mitochondrial genome of Aedes flavopictus (Yamada, 1921) (Diptera: Culicidae) collected in South Korea.

In this study, we determined for the first time the mitochondrial genome sequence of an Aedes flavopictus specimen collected in South Korea. Its mitochondrial genome was 16,060 bp in length, consisting of 13 protein-coding, 22 tRNA, and 2 rRNA genes and a non-coding A + T rich region. The overall base composition in the heavy strand was 39.7, 8.6, 12.7, and 39% of A, G, C, and T, respectively, and the G + C content was 21.2%. Phylogenetic analysis revealed that Aedes spp. formed a monophyletic clade.

Complete mitochondrial genome of Cyclograpsus intermedius Ortmann, 1894 (Crustacea: Decapoda: Grapsoidea) specimen collected in South Korea.

In this study, the complete 16,184 bp mitochondrial genome of Cyclograpsus intermedius was determined from a specimen collected in South Korea. It consists of 13 protein-coding, 22 tRNA, 2 rRNA genes, and a non-coding A + T rich region. The base composition of the heavy strand in the mitochondrial genome was 34.7% A, 10.7% G, 18.7% C, and 35.9% T, resulting in a G + C content of 29.4%. A maximum-likelihood phylogenetic tree based on the 13 mitochondrial protein-coding genes showed that C. intermedius clustered together with the Varunidae. These molecular data will be useful for studying the evolutionary relationships among crab species.

Complete mitochondrial genome of the mantis shrimp Taku spinosocarinatus (Fukuda, 1909) (Stomatopoda: Gonodactyloidea: Takuidae) in South Korea.

The superfamily Gonodactyloidea is polyphyletic because of Hemisquillidae, but to date, mitochondrial genome of that family does not exist. As valuable data that can be compared in the future with that family within this superfamily, we report the first complete mitochondrial genome sequence of Taku spinosocarinatus of the family Takuidae. The mitochondrial genome is 15,960 bp in length and consists of 13 protein-coding genes (PCGs), 22 transfer RNA genes, 2 ribosomal RNA genes, and a non-coding A + T rich region. The overall base composition in the heavy strand was as follows: A: 34.2%, G: 13.4%, C: 19.8%, and T: 32.6%, with a G + C content of 33.2%. Phylogenetic analysis revealed that this species was most closely related to Gonodactylus chiragra of Gonodactylidae, registered with NCBI to date. The result of this study will enable additional comparisons between families in the future.

Complete mitochondrial genome of the mantis shrimp, Chorisquilla orientalis Hwang, Ahyong, & Kim, 2018 (Stomatopoda: Protosquillidae).

In this study, we determined the mitochondrial genome of a stomatopod, Chorisquilla orientalis, collected from Korean waters. The complete mitochondrial genome comprised 15,880 bp, encoding 13 proteins, 22 transfer RNAs, 2 ribosomal RNAs genes, and a non-coding A + T rich region. The overall base composition in the heavy strand was A: 35.5%, G: 12.4%, C: 18.3%, and T: 33.7%, with a G + C content of 30.8%. Phylogenetic analysis showed that C. orientalis belonged to the families Gonodactylidae and Takuidae in the same clade, and to the superfamily Gonodactyloidea within Stomatopoda. This is the first record of the complete mitochondrial genome sequence of the family Protosquillidae.

Phylogeographic studies on two shore crab species from East Asia: similar but different stories.

BACKGROUND: The genetic structure of marine organisms in the East Asian region has long been a subject of interest. Two grapsid crab species, Hemigrapsus penicillatus (De Haan, 1835) and Hemigrapsus sanguineus (De Haan, 1835), are commonly found in the rocky intertidal zones around this region. They are known to spread via larval migration, which makes them an appropriate model species for observing the genetic structure of East Asian intertidal invertebrate animals. OBJECTIVE: We investigated the genetic structure of the East Asian crabs H. penicillatus and H. sanguineus. METHODS: We collected specimens of H. penicillatus from seven locations (42 individuals) and of H. sanguineus from ten locations (58 individuals) in Korea, Japan, and Taiwan. We investigated and compared the genetic diversity and structure of populations of these species using mitochondrial cytochrome oxidase subunit I (COI) sequences. RESULTS: Our results show that both species are genetically structured between South Korea and Japan, and that the Taiwan population forms a cluster that is separate from those of the other countries. Populations of H. penicillatus contain less genetic diversity than those of H. sanguineus. CONCLUSION: These results suggest that there is a genetic structure between the two species at present in East Asia.