Sunghoon Jung

COI barcoding of true bugs (Insecta, Heteroptera)

Several recent studies have proposed that partial DNA sequences of the cytochrome c oxidase I (COI) mitochondrial gene might serve as DNA barcodes for identifying and differentiating between animal species, such as birds, fish and insects. In this study, we tested the effectiveness of a COI barcode to identify true bugs from 139 species collected from Korea and adjacent regions (Japan, Northeastern China and Fareast Russia). All the species had a unique COI barcode sequence except for the genus Apolygus (Miridae), and the average interspecific genetic distance between closely related species was about 16 times higher than the average intraspecific genetic distance. DNA barcoding identified one probable new species of true bug and revealed identical or very recently divergent species that were clearly distinguished by morphological characteristics. Therefore, our results suggest that COI barcodes can reveal new cryptic true bug species and are able to contribute for the exact identification of the true bugs.

Molecular phylogeny of the plant bugs (Heteroptera: Miridae) and the evolution of feeding habits

The first comprehensive cladistic analysis of Miridae, the plant bugs, is presented based on analysis of 3935 base pairs of mitochondrial (16S, COI) and nuclear (18S, 28SD3) DNA for 91 taxa in seven subfamilies. Data were analysed using maximum likelihood (ML), parsimony and Bayesian inference (BI) phylogenetic frameworks. The phylogenetic results are compared with previous hypotheses of higher relationships in the family using alternative hypothesis tests. A Bayesian relaxed molecular clock is used to examine divergence times, and ancestral feeding habits are reconstructed using parsimony and a Bayesian approach. Clades recovered in all analyses are as follows: Cimicomorpha, Miroidea and Miridae; Bryocorinae: Bryocorini; Stenodemini; Mirinae; Deraeocorinae (Clevinemini + Deraeocorini); Cylapinae; Isometopinae; Bryocorinae: Dicyphini; Orthotylini; Phylinae (Phylini + Pilophorini), and Phylinae as sister group to all the remaining mirid taxa. These results are largely congruent with former hypotheses based on morphological data with respect to the monophyly of various subfamilies and tribes; however, our results indicate that the subfamily Bryocorinae is not monophyletic, as the two tribes, Dicypini and Bryocorini, were separated in the phylogenetic results. Divergence time estimates indicate that the radiation of the Miridae began in the Permian; most genus‐level radiations within subfamilies began in the late Cretaceous, probably in response to the angiosperm radiation. Ancestral feeding state reconstructions based on Bayesian and parsimony inference were largely congruent and both reconstructed phytophagy as the ancestral state of the Miridae. Furthermore, the feeding habits of the common ancestors of Mirinae + Deraeocorinae, Bryocorinae + Cylapinae + Isometopinae + Orthotylinae, and the remaining taxa excluding Phylinae, were inferred as phytophagous. Therefore, at least three shifts from phytophagy or polyphagy to predation occurred within the Miridae. Additionally, based on the mirid host‐plant records, we discovered several trends, such as a strong relationship between host‐plant ranges and a facultative feeding habit.

Molecular phylogeny and evolutionary habitat transition of the flower bugs (Heteroptera: Anthocoridae).

We performed a molecular phylogenetic study of the Anthocoridae, the flower bugs, based on maximum likelihood, maximum parsimony, and Bayesian analyses of ∼ 3000 base pairs (bp) of DNA sequence from the mitochondrial 16S rRNA and nuclear 18S rRNA and 28S rRNA genes for 44 taxa. Our phylogenetic analyses indicates that (i) the tribe Cardiastethini (Dufouriellini) could be a paraphyletic group, as the genera Amphiareus and Dysepicritus are not included in the tribe; (ii) the main subgroups, Oriini and Anthocorini, are monophyletic within Anthocoridae; (iii) three tribes of Blaptostethini, Xylocorini, and Scolopini are separated from the main anthocorid clade which is composed of Anthocorini, Cardiastethini, and Oriini, suggesting that Anthocoridae could not be monophyletic. We compared our molecular phylogeny to previous hypotheses of evolutionary relationships within Cimicoidea based on different anthocorid classification systems using alternative hypothesis tests (Kishino-Hasegawa and Shimodaira-Hasegawa tests). BayesTraits were used to examine the ancestral character states inferring historical habitat patterns of the Anthocoridae. Reconstruction of the ancestral habitat patterns of the Anthocoridae suggests that dead plants may have served as an important habitat for the common ancestor of anthocorids. The biological events such as diversification of angiosperms and anthocorid prey might have provided anthocorids with more habitat options, such as living plants; thereafter, Anthocorini and Amphiareus appeared to have evolved increasingly specialized habitat relationships.

Effect of electron transport layer crystallinity on the transient characteristics of inverted organic solar cells

We present how the crystallinity of the electron transport layer can dramatically influence the transient characteristics of organic solar cells. We employed an inverted cell structure using TiOx prepared by atomic layer deposition as an electron transport layer. The device possessing the amorphous phase TiOx exhibited a continuous increase in the device characteristics upon continuous illumination at ambient, which is attributed to the filling of shallow electron traps within the amorphous phase TiOx upon illumination. In contrast, the characteristics of the device with the crystalline phase TiOx showed a negligible increase upon continuous illumination.

Correlated evolution and Bayesian divergence time estimates of the Cimicoidea (Heteroptera: Cimicomorpha) reveal the evolutionary history

The diverse habitat types and discrete morphological characters of cimicoid species provide a unique opportunity to study correlated evolution. Phylogenetic relationships within Cimicoidea were determined using Bayesian analyses of molecular data, allowing the generation of testable hypotheses of correlated evolution. An investigation of the correlation between habitat selection and morphological characters revealed that a dead plant habitat was correlated with the filiform antennal type. Furthermore, molecular dating analysis was used to examine divergence times within the Cimicoidea. Transitions to live plants from dead plants for most cimicoid clades started right after the mid‐Cretaceous, coinciding with the radiation of the angiosperms. Using contingency analyses, we determined that evolutionary changes in morphological characters were dependent on habitat selection. Based on these results, we propose evolutionary historical hypotheses for the Cimicoidea.

Infrared spectroscopy of the interface charge in a ZnO field-effect transistor

We used far-infrared transmission spectroscopy to probe the electrostatically induced charge carriers in a ZnO field-effect transistor. The carrier absorption spectrum exhibits a non-Drude, incoherent conduction behavior at low gate-source voltages (VGS<40V), which evolves toward a standard Drude behavior as VGS is increased. This change is explained successfully by a generalized Drude model. We find that the interface carriers undergo strong backscattering collisions during the channel conduction and the microscopic scattering angle changes with VGS.

Molecular identification of dipteran pests (Diptera: Sciaroidea) from shiitake mushroom

On shiitake farms, mycophagous maggots can cause serious damage by preventing formation of the fruiting body. Recently, these pests have significantly reduced shiitake production in Korea. However, larvae and female adults cannot be identified due to their lack of morphological characteristics. Therefore, farmers and applied entomologists are unable to determine which species is the primary cause of the shiitake damage. In this study, mycophagous flies (colonized larvae) were collected from damaged shiitake farms and subsequently identified by matching identified males with the cytochrome c oxidase subunit I (COI) sequences from the larvae. Divergences of the COI sequences among the species discriminated the clusters clearly, and the mycophagous pests were identified as Camptomyia corticalis and C. heterobia. Interestingly, these two species coexisted under the bark of shiitake oak bed logs.

New Record of the Family Lasiochilidae Carayon, 1972 (Hemiptera: Cimicoidea) from the Korean Peninsula, with Re-Description of Lasiochilus (Dilasia) japonicusfrom Jeju Island

Abstract Herein, Lasiochilus (Dilasia) japonicus Hiura 1967 is recognized for the first time on the Korean Peninsula. This insect is a member of the Family Lasiochilidae, which is new to the Korean Peninsula. Both female and male adults are re-described on the basis of specimens obtained from Jeju Island, Korea.

Phylogenetic and systematic study of Korean Orius species (Heteroptera: Anthocoridae) on the basis of molecular and morphological data

A phylogenetic and systematic study of Orius species (Heteroptera: Anthocoridae) from Korea has been conducted using both morphological and molecular characters. Thirty morphological character states were coded for 10 strains of 9 species. Five molecular markers, partial cytochrome c oxidase I (COI), cytochrome b (CytB), 16S rRNA (16S), 18S rRNA (18S), and 28S rRNA (28S), from mitochondrial and nuclear genes, were tested. Phylogenetic analyses based on molecular data were conducted by minimum evolution, maximum parsimony, maximum likelihood, and Bayesian phylogenetic (BP) analyses. Analysis of morphological data was performed using the parsimony programs NONA, and the combined dataset of morphological and molecular data was analyzed using BP analyses. The results of this study indicate that use of COI and CytB enabled relatively effective identification of species, whereas the sequences of 16S, 18S and 28S did not enable identification of closely related species such as Orius minutus and O. strigicollis. We discuss the usefulness of the five molecular markers for determining phylogenetic relationships and identifying the species.

Ferromagnetism and infrared conductivity of the homogeneous hexaboride alloy Eu1?xCaxB6

We have studied the magnetic and optical properties of hexaboride Eu1−xCaxB6 for x = 0, 0.13, 0.25, 0.35, 0.54 and 1.0 from measurements of dc magnetization and wide-range absolute reflectivity. The ferromagnetic transition temperature Tc decreases with Ca-doping and is completely suppressed when x exceeds 0.35. The Drude plasma frequency ωp2 also decreases with x and disappears at the same composition. We have analysed this correlation between Tc and ωp2 in terms of the RKKY theory. We have also simulated optical spectra of Eu1−xCaxB6 using the effective medium theory and compare them with the measured data. The results show that Eu1−xCaxB6 is not a composite of EuB6 and CaB6 but forms a homogeneous magnetic alloy.