The genomic history and global migration of a windborne pest.

Many insect pests, including the brown planthopper (BPH), undergo windborne migration that is challenging to observe and track. It remains controversial about their migration patterns and largely unknown regarding the underlying genetic basis. By analyzing 360 whole genomes from around the globe, we clarify the genetic sources of worldwide BPHs and illuminate a landscape of BPH migration showing that East Asian populations perform closed-circuit journeys between Indochina and the Far East, while populations of Malay Archipelago and South Asia undergo one-way migration to Indochina. We further find round-trip migration accelerates population differentiation, with highly diverged regions enriching in a gene desert chromosome that is simultaneously the speciation hotspot between BPH and related species. This study not only shows the power of applying genomic approaches to demystify the migration in windborne migrants but also enhances our understanding of how seasonal movements affect speciation and evolution in insects.

Flexible solar cells based on foldable silicon wafers with blunted edges.

Flexible solar cells have a lot of market potential for application in photovoltaics integrated into buildings and wearable electronics because they are lightweight, shockproof and self-powered. Silicon solar cells have been successfully used in large power plants. However, despite the efforts made for more than 50 years, there has been no notable progress in the development of flexible silicon solar cells because of their rigidity1-4. Here we provide a strategy for fabricating large-scale, foldable silicon wafers and manufacturing flexible solar cells. A textured crystalline silicon wafer always starts to crack at the sharp channels between surface pyramids in the marginal region of the wafer. This fact enabled us to improve the flexibility of silicon wafers by blunting the pyramidal structure in the marginal regions. This edge-blunting technique enables commercial production of large-scale (>240 cm2), high-efficiency (>24%) silicon solar cells that can be rolled similarly to a sheet of paper. The cells retain 100% of their power conversion efficiency after 1,000 side-to-side bending cycles. After being assembled into large (>10,000 cm2) flexible modules, these cells retain 99.62% of their power after thermal cycling between -70 °C and 85 °C for 120 h. Furthermore, they retain 96.03% of their power after 20 min of exposure to air flow when attached to a soft gasbag, which models wind blowing during a violent storm.

CPR Gene Contributes to Integument Function and Ovary Development in a Rice Planthopper.

Nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductase (CPR) is an essential enzyme that transfers electrons from NADPH to cytochrome P450 monooxygenases. CPR is involved in cuticular hydrocarbon (CHC) synthesis in insects and is vital for insect development and survival. Here, we clarify the physiological function of a CPR gene in Nilaparvata lugens, an important rice pest, by using RNA interference. CPR gene knockdown leads to the functional loss of waterproofing and water retention in the integument of female adults, which causes significantly reduced body weight and a lethal phenotype. Scanning electron microscopy shows that the lipid layer on the outermost surface of the abdominal cuticle becomes thin in dsCPR-injected adults. Furthermore, CHC profile analysis reveals that CPR knockdown significantly decreases the contents of CHCs with a carbon chain length ≥ C27 in adult females. Moreover, we find that CPR knockdown generates a deficient phenotype in ovaries with deformed oocytes and a complete failure of egg-laying. These findings suggest that CPR plays multiple functional roles in CHC biosynthesis and embryo development in insects.

A CYP380C10 gene is required for waterproofing and water retention in the insect integument.

Cuticular hydrocarbons (CHCs) are important components in the integument of insects and are required for development and survival. Insect-specific CYP4G subfamily, of the P450 enzymes, catalyze the oxidative decarbonylation step in the biosynthesis of CHCs. Here, we characterized CYP380C10 gene function in a Hemiptera rice pest, Nilaparvata lugens. We used RNA interference-mediated expression silencing to reveal that NlCYP380C10 played a key role in waterproofing and water-retention in the integument of N. lugens. Knockdown of NlCYP380C10 significantly reduced body weight and caused mortality. Scanning electron microscopy showed the loss of the lipid layer on the surface of the abdominal cuticle of the dsNlCYP380C10-injected adults. Furthermore, CHC profile analysis revealed that NlCYP380C10 knockdown significantly decreased the amounts of CHCs in adult females. This suggested that NlCYP380C10 was involved in CHC biosynthesis. Reduction of CHC content caused the loss of the intact lipid layer of the cuticle, which resulted in loss of the waterproofing and water-retention functions. This led to failure of molting and eclosion. Our findings expanded the knowledge of CHC biosynthesis in the insect integument and led to a better understanding of the functional roles of CYP450 genes involved in waterproofing and water-retention in insects.

Cuticular Hydrocarbon Plasticity in Three Rice Planthopper Species.

Insect cuticular hydrocarbons (CHCs) are organic compounds of the surface lipid layer, which function as a barrier against water loss and xenobiotic penetration, while also serving as chemical signals. Plasticity of CHC profiles can vary depending upon numerous biological and environmental factors. Here, we investigated potential sources of variation in CHC profiles of Nilaparvata lugens, Laodelphax striatellus and Sogatella furcifera, which are considered to be the most important rice pests in Asia. CHC profiles were quantified by GC/MS, and factors associated with variations were explored by conducting principal component analysis (PCA). Transcriptomes were further compared under different environmental conditions. The results demonstrated that CHC profiles differ among three species and change with different developmental stages, sexes, temperature, humidity and host plants. Genes involved in cuticular lipid biosynthesis pathways are modulated, which might explain why CHC profiles vary among species under different environments. Our study illustrates some biological and ecological variations in modifying CHC profiles, and the underlying molecular regulation mechanisms of the planthoppers in coping with changes of environmental conditions, which is of great importance for identifying potential vulnerabilities relating to pest ecology and developing novel pest management strategies.

Identification of novel antimicrobial peptides from rice planthopper, Nilaparvata lugens.

In this study, two novel antibacterial peptide genes, termed lugensin A and B were identified and characterized from a rice sap-sucking hemipteran insect pest, the brown planthopper, Nilaparvata lugens. Lugensin gene expression was significantly induced by Gram-negative and Gram-positive bacterial stains under the regulation of a signal receptor, the long peptidoglycan recognition protein (PGRP-LC) in the IMD pathway. Knockdown of PGRP-LC by RNAi eliminated bacterium induced Lugensin gene expression. Lugensins had the apparent antibacterial activities against Escherichia coli K12, Bacillus subtilis and the rice bacterial brown stripe pathogen Acidovorax avenae subsp. avenae (Aaa) strain RS-1. Lugensins inhibited bacterial proliferation by disrupting the integrity of the bacterial membranes. Scanning electron microscopy revealed abnormal membrane morphology of the recombinant Lugensin-treated bacteria. Lugensins induced complete cell disruption of E. coli K12 and B. subtilis strains while formed the holes on the cell surface of Aaa RS-1 strain. Immunofluorescence showed that Lugensins localized in the cell membrane of E. coli K12 while accumulated in the cytosol of B. subtilis. Differently, Lugensins remained in both the cell membrane and the cytosol of Aaa RS-1 strain, suggesting different action modes of Lugensins to different microbes. This is the first report of the novel antibacterial peptides found in the rice sap-sucking hemipteran insect species.

A III-V-on-Si ultra-dense comb laser.

Optical frequency combs emerge as a promising technology that enables highly sensitive, near-real-time spectroscopy with a high resolution. The currently available comb generators are mostly based on bulky and high-cost femtosecond lasers for dense comb generation (line spacing in the range of 100 MHz to 1 GHz). However, their integrated and low-cost counterparts, which are integrated semiconductor mode-locked lasers, are limited by their large comb spacing, small number of lines and broad optical linewidth. In this study, we report a demonstration of a III-V-on-Si comb laser that can function as a compact, low-cost frequency comb generator after frequency stabilization. The use of low-loss passive silicon waveguides enables the integration of a long laser cavity, which enables the laser to be locked in the passive mode at a record-low 1 GHz repetition rate. The 12-nm 10-dB output optical spectrum and the notably small optical mode spacing results in a dense optical comb that consists of over 1400 equally spaced optical lines. The sub-kHz 10-dB radio frequency linewidth and the narrow longitudinal mode linewidth (<400 kHz) indicate notably stable mode-locking. Such integrated dense comb lasers are very promising, for example, for high-resolution and real-time spectroscopy applications.

Room Temperature O-band DFB Laser Array Directly Grown on (001) Silicon.

Several approaches for growing III-V lasers on silicon were recently demonstrated. Most are not compatible with further integration, however, and rely on thick buffer layers and require special substrates. Recently, we demonstrated a novel approach for growing high quality InP without buffer on standard 001-silicon substrates using a selective growth process compatible with integration. Here we show high quality InGaAs layers can be grown on these InP-templates. High-resolution TEM analysis shows these layers are free of optically active defects. Contrary to InP, the InGaAs material exhibits strong photoluminescence for wavelengths relevant for integration with silicon photonics integrated circuits. Distributed feedback lasers were defined by etching a first order grating in the top surface of the device. Clear laser operation at a single wavelength with strong suppression of side modes was demonstrated. Compared to the previously demonstrated InP lasers 65% threshold reduction is observed. Demonstration of laser arrays with linearly increasing wavelength prove the control of the process and the high quality of the material. This is an important result toward realizing fully integrated photonic ICs on silicon substrates.

360 deg full-parallax light-field display using panoramic camera.

One of the common approaches to achieving vertical parallax for the horizontal-parallax-only light-field display is to introduce the viewer-tracking method. A panoramic camera is assembled in a 360 deg scanning light-field display system for the full-parallax demand in this study, wherein the image generation algorithm is improved to be sensitive to multiple viewer positions, and the tracking and rendering are processed in real time. The horizontal-parallax-only light-field display using a panoramic camera is determined to be able to achieve smooth and consecutive full-parallax performance for multiple viewers in a 360 deg range.

Genomic insights into the serine protease gene family and expression profile analysis in the planthopper, Nilaparvata lugens.

BACKGROUND: The brown planthopper (Nilaparvata lugens) is one of the most destructive rice plant pests in Asia. N. lugens causes extensive damage to rice by sucking rice phloem sap, which results in hopper burn (complete death of the rice plants). Despite its importance, little is known about the digestion, development and defense mechanisms of this hemimetabolous insect pest. In this study, we aim to identify the serine protease (SP) and serine protease homolog (SPH) genes, which form a large family in eukaryotes, due to the potential for multiple physiological roles. Having a fully sequenced genome for N. lugens allows us to perform in-depth analysis of the gene structures, reveal the evolutionary relationships and predict the physiological functions of SP genes. RESULTS: The genome- and transcriptome-wide analysis identified 90 putative SP (65) and SPH (25) genes in N. lugens. Detailed gene information regarding the exon-intron organization, size, distribution and transcription orientation in the genome revealed that many SP/SPH loci are closely situated on the same scaffold, indicating the frequent occurrence of gene duplications in this large gene family. The gene expression profiles revealed new findings with regard to how SPs/SPHs respond to bacterial infections as well as their tissue-, development- and sex-specific expressions. CONCLUSIONS: Our findings provide comprehensive gene sequence resources and expression profiles of the N. lugens SP and SPH genes, which give insights into clarifying the potentially functional roles of these genes in the biological processes including development, digestion, reproduction and immunity.

Polytypic InP nanolaser monolithically integrated on (001) silicon.

On-chip optical interconnects still miss a high-performance laser monolithically integrated on silicon. Here, we demonstrate a silicon-integrated InP nanolaser that operates at room temperature with a low threshold of 1.69 pJ and a large spontaneous emission factor of 0.04. An epitaxial scheme to grow relatively thick InP nanowires on (001) silicon is developed. The zincblende/wurtzite crystal phase polytypism and the formed type II heterostructures are found to promote lasing over a wide wavelength range.

Sub-µm2 power splitters by using silicon hybrid plasmonic waveguides.

Nano-scale power splitters based on Si hybrid plasmonic waveguides are designed by utilizing the multimode interference (MMI) effect as well as Y-branch structure. A three-dimensional finite-difference time-domain method is used for simulating the light propagation and optimizing the structural parameters. The designed 1 × 2 50:50 MMI power splitter has a nano-scale size of only 650 nm × 530 nm. The designed Y-branch power splitter is also very small, i.e., about 900 nm × 600 nm. The fabrication tolerance is also analyzed and it is shown that the tolerance of the waveguide width is much larger than±50 nm. The power splitter has a very broad band of over 500 nm. In order to achieve a variable power splitting ratio, a 2×2 two-mode interference coupler and an asymmetric Y-branch are used and the corresponding power splitting ratio can be tuned in the range of 97.1%:2.9%-1.7%:98.3% and 84%:16%-16%:84%, respectively. Finally a 1×4 power splitter with a device footprint of 1.9 µm × 2.6 µm is also presented using cascaded Y-branches.

Highly efficient nonuniform grating coupler for silicon-on-insulator nanophotonic circuits.

We present design, fabrication, and characterization of a silicon-on-insulator grating coupler of high efficiency for coupling between a silicon nanophotonic waveguide and a single mode fiber. By utilizing the lag effect of the dry etching process, a grating coupler consisting of nonuniform grooves with different widths and depths is designed and fabricated to maximize the overlapping between the upward wave and the fiber mode. The measured waveguide-to-fiber coupling efficiency of 64% (-1.9 dB) for the transverse electric polarization is achieved by the present nonuniform grating coupler directly defined on a regular silicon-on-insulator wafer.

Ultracompact low-loss coupler between strip and slot waveguides.

We present both theoretical and experimental results of an ultracompact waveguide coupler that is capable of highly efficient coupling of light from strip waveguides to slot waveguides, and vice versa. By optimizing the geometrical parameters, it is possible to achieve extremely low-loss coupling. A coupling efficiency of 97% has been obtained experimentally while keeping the overall size down to the range below 10 mum. Further analysis shows that the proposed coupler has relatively high tolerance to fabrication errors and is wavelength insensitive.