N6-methyladenosine modification of the mRNA for a key gene in purine nucleotide metabolism regulates virus proliferation in an insect vector.

The titer of viruses that persist and propagate in their insect vector must be high enough for transmission yet not harm the insect, but the mechanism of this dynamic balance is unclear. Here, expression of inosine monophosphate dehydrogenase (LsIMPDH), a rate-limiting enzyme for guanosine triphosphate (GTP) synthesis, is shown to be downregulated by increased levels of N6-methyladenosine (m6A) on LsIMPDH mRNA in rice stripe virus (RSV)-infected small brown planthoppers (SBPHs; Laodelphax striatellus), the RSV vector, which decreases GTP content, thus limiting viral proliferation. Moreover, planthopper methyltransferase-like protein 3 (LsMETTL3) and m6A reader protein LsYTHDF3 are found to catalyze and recognize the m6A on LsIMPDH mRNA, respectively, and cooperate in destabilizing LsIMPDH transcripts. Co-silencing assays show that negative regulation of viral proliferation by both LsMETTL3 and LsYTHDF3 is partially dependent on LsIMPDH. This distinct mechanism limits virus replication in an insect vector, providing a potential gene target to block viral transmission.

Sublethal Effects of Thiamethoxam on Biological Traits and Detoxification Enzyme Activities in the Small Brown Planthopper, Laodelphax striatellus (Fallén).

The small brown planthopper (Laodelphax striatellus (Fallén), Hemiptera: Delphacidae), is an important agricultural pest of rice, and neonicotinoid insecticides are commonly used for controlling L. striatellus. However, the sublethal effects of thiamethoxam on L. striatellus remain relatively unknown. In this study, an age-stage life table procedure was used to evaluate the sublethal effects of thiamethoxam on the biological parameters of L. striatellus. Additionally, activities of carboxylesterase, glutathione S-transferase, and cytochrome P450 monooxygenase in the third instar nymphs were analyzed. The results indicated that the survival time of F0 adults and the fecundity of female adults decreased significantly after the third instar nymphs were treated with sublethal concentrations of thiamethoxam (LC15 0.428 mg/liter and LC30 0.820 mg/liter). The developmental duration, adult preoviposition period, total preoviposition period, and mean generation time of the F1 generation increased significantly, whereas the fecundity of the female adults, intrinsic rate of increase (ri), and finite rate of increase (λ) decreased significantly. The oviposition period was significantly shorter for the insects treated with LC30 than for the control insects. Neither sublethal concentrations had significant effects on the adult longevity, net reproduction rate (R0), or gross reproduction rate (GRR) of the F1 generation. The activities of carboxylesterase, glutathione-S-transferase, and cytochrome P450 monooxygenase increased significantly after the thiamethoxam treatments. These results indicate that sublethal concentrations of thiamethoxam can inhibit L. striatellus population growth and enhance detoxification enzyme activities.

One new species of the genus Etielloides Shibuya, 1928 from China (Lepidoptera, Pyralidae, Phycitinae).

One new species, Etielloides luniformis sp. nov. is described based on specimens collected from Mt. Leigong, Qiandongnan Miao and Dong Autonomous Prefecture, Guizhou of China. Adults, venation, head and genitalia structures of both sexes are described and illustrated, along with a key to all the known species of the genus Etielloides. DNA barcodes of the new species and its related species are provided for species delimitation.

Insights Into Insect Vector Transmission and Epidemiology of Plant-Infecting Fijiviruses.

Viruses in genus Fijivirus (family Reoviridae) have caused serious damage to rice, maize and sugarcane in American, Asian, European and Oceanian countries, where seven plant-infecting and two insect-specific viruses have been reported. Because the planthopper vectors are the only means of virus spread in nature, their migration and efficient transmission of these viruses among different crops or gramineous weeds in a persistent propagative manner are obligatory for virus epidemics. Understanding the mechanisms of virus transmission by these insect vectors is thus key for managing the spread of virus. This review describes current understandings of main fijiviruses and their insect vectors, transmission characteristics, effects of viruses on the behavior and physiology of vector insects, molecular transmission mechanisms. The relationships among transmission, virus epidemics and management are also discussed. To better understand fijivirus-plant disease system, research needs to focus on the complex interactions among the virus, insect vector, insect microbes, and plants.

Taxonomic review of the genus Dusungwua Kemal, Kizildag Koçak, 2020 (Lepidoptera: Pyralidae), with descriptions of six new species and propositions of synonyms.

Eleven species of the genus Dusungwua Kemal, Kizildag Koçak 2020 in China are reviewed with emendation of the generic charaters. Among them, six new species, Dusungwua antennalveata Ren Li, sp. nov., D. basinigra Ren Li, sp. nov., D. fascecornuta Ren Li, sp. nov., D. paripalpa Ren Li, sp. nov., D. similiquadrangula Ren Li, sp. nov. and D. strictivinculum Ren Li, sp. nov. are described as new to science. Also, the following taxonomic changes are proposed: Eurhodope pseudodichromella Yamanaka, 1980 syn. nov. is synonymized with D. dichromella (Ragonot, 1893), Trachycera nipponella Yamanaka, 2000 syn. nov., Trachycera vicinella Yamanaka, 2000 syn. nov. and Trachycera yakushimensis Yamanaka, 2000 syn. nov. are synonymized with D. paradichromella (Yamanaka, 1980). The female of D. quadrangula (Du, Sung Wu, 2005) is described for the first time. Photos of adults as well as male and female genitalia are provided, along with a key to the Chinese species and a distibution map to show the localities of these species.

A new species of Pima Hulst, 1888 from China (Lepidoptera, Pyralidae, Phycitinae), with a key to Holarctic species.

Pima tristriata sp. nov. is described as new to science based on specimens collected from the Ningxia Hui Autonomous Region, China, and P. boisduvaliella (Guenée, 1845) is also treated here for comparison. DNA barcodes of the two species are provided, together with a neighbor-joining tree for species delimitation. A key to the Holarctic species and a distribution map of the Chinese species are presented.

Rice black-streaked dwarf virus: From multiparty interactions among plant-virus-vector to intermittent epidemics.

Rice black-streaked dwarf virus (RBSDV) (species Rice black-streaked dwarf virus, genus Fijivirus, family Reoviridae) is the causal agent of rice black-streaked dwarf and maize rough dwarf diseases, which occur in intermittent epidemics in East Asian countries and are responsible for considerable yield losses. Intermittency of epidemics make accurate forecasting and designing of effective management strategies difficult. However, recent insights into host-virus-vector insect interactions are now informing forecasting and disease control measures. Resistance genes are also being identified and mapped. SYMPTOMATOLOGY AND HOST RANGE: RBSDV induces extreme stunting, darkened, and stiff leaves of crops and weeds only in the family Poaceae, including Oryza sativa, Zea mays, and Triticum aestivum. Infected plants produce totally or partially deformed panicles and remain alive through harvest. GENOME AND GENE FUNCTION: The nonenveloped virus particles comprise a double-layered capsid, 50-nm core with genomic double-stranded RNA (dsRNA), and six proteins. The genome of RBSDV contains 10 segments of dsRNA, named S1 to S10 in decreasing order of molecular weight. Segments 1, 2, 3, 4, 6, 8, and 10 encode the RNA-dependent RNA polymerase (RdRp), the major core structural protein, a protein with guanylyltransferase activity, an outer-shell B-spike protein, viral RNA-silencing suppressor, the major capsid protein, and the outer capsid protein, respectively. Each of the segments 5, 7, and 9 encodes two proteins: P5-1, a component of viroplasms; P5-2 of unknown function; nonstructural protein P7-1, involved in forming the structural matrix of tubular structures in infected tissues; P7-2 of unknown function; P9-1, the main component of viroplasms in infected cells and involved in viral replication; and P9-2 of unknown function. TRANSMISSION AND EPIDEMIOLOGY: RBSDV is transmitted by Laodelphax striatellus in a persistent propagative manner. The vector insect is the only means of virus spread in nature, so its migration and transmission efficiency are obligatory for disease epidemics to develop. Susceptible varieties are widely planted, but efficient transmission by vectors is the primary reason for the epidemics. Cultivation system, pesticide overuse, and climatic conditions also contribute to epidemics by affecting the development of the vector insects and their population dynamics. DISEASE MANAGEMENT: In the absence of resistant varieties, integrated disease management aims at disrupting the cycle of virus transmission by the insect vector. Inheritance studies have indicated that resistance is mostly governed by quantitative trait loci or multiple genes. Genetic engineering through RNA-interference and gene-editing strategies are potential approaches for disease control.

High Diversity and Functional Complementation of Alimentary Canal Microbiota Ensure Small Brown Planthopper to Adapt Different Biogeographic Environments.

Almost all insects harbor commensal bacteria in the alimentary canal lumen or within cells and often play a pivotal role in their host's development, evolution, and environmental adaptation. However, little is known about the alimentary canal microbiota and their functions in sap-sucking insect pests of crops, which can damage plants by removing plant sap and by transmitting various plant viruses, especially in the small brown planthopper, Laodelphax striatellus. In this study, we characterized the alimentary canal microbiota of L. striatellus collected from seven regions in China by sequencing 16S rDNA. The insects harbored a rich diversity of microbes, mainly consisted of bacteria from phyla Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, and Tenericutes. The composition and abundance of microbiota were more similar as the geographic distance decreased between the populations and clustered by geographic location into three groups: temperate, subtropical, and tropical populations. Although the abundance and species of microbes differed among the populations, the various major microbes for each population performed similar functions based on a clusters of orthologous group analysis. Greater diversity in ecological factors in different regions might lead to higher microbial diversity, thus enabling L. striatellus to adapt or tolerate various extreme environments to avoid the cost of long-distance migration. Moreover, the abundance of various metabolic functions in the Kaifeng populations might contribute to higher fecundity in L. striatellus.

Two new species, one unrecorded species, and one newly reported male of genus Thiallela Walker, 1863 from China (Lepidoptera: Pyralidae: Phycitinae).

The genus Thiallela Walker is a small genus with ten named species, and four of them were currently recorded from China. In the present study our new discoveries bring the total described species to twelve, with two (Thiallela celadontis sp. nov. and T. sulciflagella sp. nov.) being proposed as new, and one (T. ligeralis (Walker)) newly recorded in China. The male of T. epicrociella (Strand) is described for the first time. Photographs of the adults and the genital structures of the four species are provided. A world catalog of the genus Thiallela, a distribution map of and keys to the species known from China are also provided.

Two Negative-Strand RNA Viruses Identified in Watermelon Represent a Novel Clade in the Order Bunyavirales.

Two novel negative-sense, single-stranded (ss) RNA viruses were identified in watermelon plants and named watermelon crinkle leaf-associated virus 1 and 2 (WCLaV-1 and -2), respectively. The multipartite genomes consist of three RNA molecules of ~6.8, 1.4, and 1.3 kb. The genomes and the deduced proteins of RNA1 and RNA3 show features resembling those of members in the genus Phlebovirus and Tenuivirus; however, the predicted proteins encoded by RNA2 are related to the movement protein (MP) in the genus Ophiovirus and Emaravirus. Furthermore, these two viruses define a novel clade in the family Phenuiviridae, order Bunyavirales, which is phylogenetically related to the viruses in the above four genera. Moreover, after mechanical inoculation with WCLaV-1 seedlings of the natural host watermelon plants develop crinkling similar to those observed in the field. These findings enhance our understanding of the evolution and the classification of ssRNA viruses.

The complete nucleotide sequence and genome organization of a novel betaflexivirus infecting Citrullus lanatus.

The complete nucleotide sequence of a novel positive single-stranded (+ss) RNA virus, tentatively named watermelon virus A (WVA), was determined using a combination of three methods: RNA sequencing, small RNA sequencing, and Sanger sequencing. The full genome of WVA is comprised of 8,372 nucleotides (nt), excluding the poly (A) tail, and contains four open reading frames (ORFs). The largest ORF, ORF1 encodes a putative replication-associated polyprotein (RP) with three conserved domains. ORF2 and ORF4 encode a movement protein (MP) and coat protein (CP), respectively. The putative product encoded by ORF3, of an estimated molecular mass of 25 kDa, has no significant similarity with other proteins. Identity and phylogenetic analysis indicate that WVA is a new virus, closely related to members of the family Betaflexiviridae. However, the final taxonomic allocation of WVA within the family is yet to be determined.

The genomic and biological characterization of Citrullus lanatus cryptic virus infecting watermelon in China.

A dsRNA virus was detected in the watermelon (Citrullus lanatus) samples collected from Kaifeng, Henan province, China through the use of next generation sequencing of small RNAs. The complete genome of this virus is comprised of dsRNA-1 (1603nt) and dsRNA-2 (1466nt), both of which are single open reading frames and potentially encode a 54.2kDa RNA-dependent RNA polymerase (RdRp) and a 45.9kDa coat protein (CP), respectively. The RdRp and CP share the highest amino acid identities 85.3% and 75.4% with a previously reported Israeli strain Citrullus lanatus cryptic virus (CiLCV), respectively. Genome comparisons indicate that this virus is the same species with CiLCV, whereas the reported sequences of the Israeli strain of CiLCV are partial, and our newly identified sequences can represent the complete genome of CiLCV. Futhermore, phylogenetic tree analyses based on the RdRp sequences suggest that CiLCV is one member in the genus Deltapartitivirus, family Partitiviridae. In addition, field investigation and seed-borne bioassays show that CiLCV commonly occurs in many varieties and is transmitted though seeds at a very high rate.

Review of Pseudacrobasis Roesler, 1975 from China (Lepidoptera, Pyralidae, Phycitinae).

The genus Pseudacrobasis is reviewed for China. Pseudacrobasis dilatata sp. n. is described as new and compared with Psorosa tergestella (Ragonot, 1901). Images of adults and illustrations of genital structures are provided.

Ectomyelois Heinrich, 1956 in China, with descriptions of two new species and a key (Lepidoptera, Pyralidae, Phycitinae).

Only three species belonging to the genus Ectomyelois Heinrich, 1956 are recorded from China, of which two species, Ectomyelois bipectinalis sp. n. and Ectomyelois furvivena sp. n. are described as new. We discuss the status of Ectomyelois that has been treated as a junior synonym by previous authors; we treat it as a valid genus, revised status, based on characters of the venation and female genitalia. Photographs of the adults and illustrations of the genitalia are given, along with a key to the three known Chinese species.

Taxonomic review of the genus Indomyrlaea Roesler & Küppers 1979 of China, with descriptions of five new species (Lepidoptera: Pyralidae: Phycitinae).

The taxonomy of the Chinese species of the genus Indomyrlaea Roesler & Küppers, 1979 is revised. Five new species, namely I. bannensis Ren & Li sp. nov., I. fastigipalpa Ren & Li sp. nov., I. nigra Ren & Li sp. nov., I. proceripalpa Ren & Li sp. nov., and I. sinuapalpa Ren & Li sp. nov., are described. The following taxonomic changes are proposed: Sandrabatis Ragonot, 1893 and its type species Sandrabatis crassiella Ragonot, 1893 are synonymized with Ceroprepes Zeller, 1867 and Ceroprepes ophthalmicella (Christoph, 1881), respectively; Indomyrlaea phaeella (Hampson, 1903) comb. nov. is transferred from Sandrabatis. The original combination Nephopterix eugraphella Ragonot, 1888 is resurrected from its previous affiliation with Indomyrlaea. A checklist and a key to all the known species of the world are included.

A new subspecies and a new synonym of the genus Coladenia (Hesperiidae, Pyrginae) from China.

The second subspecies of Coladenia buchananii (de Nicéville, 1889), viz. Coladenia buchananii separafasciata Xue, Inayoshi & Hu, ssp. n., is discovered from south Jiangxi Province and west Fujian Province, southeast China. External and genital characters of both male and female of this new subspecies are illustrated and described. Coladenia neomaeniata Fan & Wang, 2006, syn. n. is proposed to be a junior synonym of Coladenia maeniata Oberthür, 1896, and the distribution of this species is briefly discussed.

iTRAQ-based quantitative proteomics analysis of rice leaves infected by Rice stripe virus reveals several proteins involved in symptom formation.

BACKGROUND: Rice plants infected by Rice stripe virus (RSV) usually leads to chlorosis and death of newly emerged leaves. However, the mechanism of RSV-induced these symptoms was not clear. METHODS: We used an iTRAQ approach for a quantitative proteomics comparison of non-infected and infected rice leaves. RT-qPCR and Northern blot analyses were performed for assessing the transcription of candidate genes. RESULTS: As a whole, 681 (65.8% downregulated, 34.2% upregulated infected vs. non-infected) differentially accumulated proteins were identified. A bioinformatics analysis indicated that ten of these regulated proteins are involved in chlorophyll biosynthesis and three in cell death processes. Subsequent RT-qPCR results showed that downregulation of magnesium chelatase was due to reduced expression levels of the genes encoding subunits CHLI and CHLD, which resulted in chlorophyll reduction involved in leaf chlorosis. Three aspartic proteases expressed higher in RSV-infected leaves than those in the control leaves, which were also implicated in RSV-induced cell death. Northern blot analyses of CHLI and p0026h03.19 confirmed the RT-qPCR results. CONCLUSIONS: The magnesium chelatase and aspartic proteases may be associated with RSV-induced leaf chlorosis and cell death, respectively. The findings may yield new insights into mechanisms underlying rice stripe disease symptom formation.

Quantification of southern rice black streaked dwarf virus and rice black streaked dwarf virus in the organs of their vector and nonvector insect over time.

Southern rice black streaked dwarf virus (SRBSDV) and rice black streaked dwarf virus (RBSDV) are serious rice-infecting reoviruses, which are transmitted by different planthoppers in a persistent propagative manner. In this study, we quantitatively compared the spatial distribution of SRBSDV and RBSDV contents over time in their vector and nonvector insects using real time-PCR. Genome equivalent copies (GEC) were assessed every 2 days from 0 to 14 days after a 3-days acquisition access period (AAP) on infected plants. Results revealed 293.2±21.6 to 404.1±46.4 SRBSDV GEC/ng total RNA in whole body of white-backed planthopper (WBPH, Sogatella furcifera) at day 0 and 12 and 513.5±88.4 to 816.8±110.7 RBSDV GEC/ng total RNA in the whole body of small brown planthopper (SBPH, Laodelphax striatellus) at day 0 and 14, respectively, after 3-days AAP. Highest GEC of both viruses were found in the gut of their respective vectors. Although SRBSDV was detected in the gut of SBPH, it did not spread into the hemolymph or other organs. After an 8-day latent period, the transmission efficiency of SRBSDV and RBSDV by their respective vectors was significantly positively correlated with GEC in the salivary gland (r(2)=0.7808, P=0.0036 and r(2)=0.9351, P<0.0001, respectively, at α=0.05). Together, these results confirm that accumulation of >200 SRBSDV or RBSDV GEC/ng total RNA in the gut of vector, indicated threshold for further spread and the virus content in the salivary gland was significantly correlated with transmission efficiency by their respective vectors.

Review of the genus Merulempista Roesler, 1967 (Lepidoptera, Pyralidae) from China, with description of two new species.

The genus Merulempista Roesler, 1967 is reviewed for China. Of the four species treated in this paper, Merulempista rubriptera Li & Ren, sp. n. and Merulempista digitata Li & Ren, sp. n. are described as new; Merulempista cyclogramma (Hampson, 1896) is newly recorded for China, and its taxonomic position is briefly discussed. Photographs of the adults and genitalia are provided, along with a key to the known Chinese species.