Molecular characterization of Vitellogenin-like1 gene in Sogatella furcifera (Hemiptera: Delphacidae), and its function on reproduction.

In this study, a vitellogenin like1 gene (SfVg-like1) in Sogatella furcifera was identified. The open reading frame (ORF) encoded 1,321 amino acid sequence. Structure analysis reveals that the amino acid sequence of SfVg-like1 has 3 conserved LPD_N, DUF1943 and VWFD domains. Phylogenetic analyses showed that SfVg-like1 was clustered in the same branch with the Vg-like1 of Nilaparvata lugens (100% bootstrap value) compared with other Hemiptera insects Vgs associated with vitellogenesis. Temporo-spatial expression analyses showed that SfVg-like1 expressed during all stages, and in both genders. The relative expression levels of SfVg-like1 mRNA were higher in adults than in nymph developmental stages. The knockdown of SfVg-like1 gene resulted in the inhibition of the ovarian development in female adults, whereas the morphology of the testis in male adults was not been affected. The silence of SfVg-like1 could decrease the relative expression levels of target of rapamycin (SfTOR, GenBank MW193765) and vitellogenin (SfVg, GenBank MH271114) genes significantly in female adults. However, the knockdown of SfTOR or SfVg genes in female adults did not affect the transcript level of SfVg-like1. Therefore, it demonstrated that SfVg-like1 might locate on the upstream signaling pathways of SfTOR and SfVg. These results demonstrate that SfVg-like1 is essential for S. furcifera reproduction, and it could be the potential target for the control of this pest.

Sogatella furcifera Saliva Mucin-like Protein Is Required for Feeding and Induces Rice Defences.

The white-backed planthopper (WBPH), Sogatella furcifera, is one of the most important piercing-sucking pests of rice (Oryza sativa) in Asia. Mucin-like salivary protein (SFMLP) is highly expressed in the salivary glands of WBPH, which plays an important role in WBPH feeding. In this study, WBPH injected with dsSFMLP had difficulty in sucking phloem sap from rice plants, which significantly reduced their food intake, weight, and survival. In contrast, the knockdown of the SFMLP gene had only a marginal effect on the survival of WBPH fed an artificial diet. Further studies showed that silencing SFMLP resulted in the short and single-branched salivary sheaths secretion and less formation of salivary flanges in rice. These data suggest that SFMLP is involved in the formation of the salivary sheath and is essential for feeding in WBPH. Overexpression of the SFMLP gene in rice plants promoted the feeding of WBPH, whereas silencing the gene in rice plants significantly decreased WBPH performance. Additionally, it was found that overexpression of SFMLP in rice plants elicited the signalling pathway of SA (salicylic acid) while suppressing JA (jasmonic acid); in contrast, silencing of the SFMLP gene in rice plants showed the opposite results. This study clarified the function of SFMLP in WBPH feeding as well as mediating rice defences.

Diversity, Tissue Localization, and Infection Pattern of Bacterial Symbionts of the White-Backed Planthopper, Sogatella furcifera (Hemiptera: Delphacidae).

The white-backed planthopper (WBPH), Sogatella furcifera (Horváth), is a destructive pest of rice. Bacterial symbionts play an important role in insect hosts, especially hemipteran hosts. This study was designed to examine the bacterial symbionts of the WBPH using 16S rDNA high-throughput sequencing. A total of 63 and 177 operational taxonomic units (OTUs) were identified in females and males of three WBPH populations, respectively. These OTUs included bacteria of 75 genera from 11 phyla, where Wolbachia, Cardinium, and Asaia were the dominant genera, accounting for over 97.99% of all the symbiotic bacteria. Fluorescence in situ hybridization detected Wolbachia, Cardinium, and Asaia in the salivary glands, guts, testes, and eggs of the WBPH, indicating the potential for both horizontal and vertical transmission. Moreover, the infection pattern of the three dominant bacterial symbionts was detected in six WBPH populations. The frequencies of Wolbachia infection of females and Cardinium infection of both sexes were over 96.7%. Wolbachia infection of males ranged between 46.7 and 63.3%, which was significantly lower than that observed for females. Asaia infection of both sexes varied substantially among the populations. These results indicate that the complex host-symbiotic bacteria interaction is influenced by host sex and geographical origin and potentially by the transmission modes of the symbionts.

Mechanisms of resistance to thiamethoxam and dinotefuran compared to imidacloprid in the brown planthopper: Roles of cytochrome P450 monooxygenase and a P450 gene CYP6ER1.

The brown planthopper (BPH, Nilaparvata lugens) has developed high resistance to the first-generation neonicotinoids (imidacloprid). With commercialization and widespread field use of the second-(thiamethoxam) and third-(dinotefuran) generation neonicotinoids, resistance to these insecticides is also reported. We investigated the cytochrome P450 monooxygenase-mediated detoxification in thiamethoxam- and dinotefuran- resistant in comparison to imidacloprid-resistant strains of BPH. In the three moderately resistant BPH strains selected separately with the three insecticides from a same susceptible strain, P450 activities were significantly enhanced over the susceptible control. Seven of 26 tested P450 genes were up-regulated and CYP6ER1 was a strongly over-expressed gene in all the three resistant strains. Knockdown of CYP6ER1 in the susceptible insects reduced P450 activity, retarded nymph growth and significantly increased sensitivity to each one of the three neonicotinoids. Taken together, we show that enhanced P450 activity and over-expression of CYP6ER1 gene are involved in BPH resistance to thiamethoxam and dinotefuran as to imidacloprid. These findings are of significance in management thiamethoxam and dinotefuran resistance in the BPH, especially in the management of potential cross-resistance to the three generations of neonicotinoids.

Low Temperature Storage of Southern Rice Black-Streaked Dwarf Virus-Infected Rice Plants Cannot Sustain Virus Transmission by the Vector.

Southern rice black-streaked dwarf virus (SRBSDV) is a novel virus transmitted by white-backed planthopper Sogatella furcifera (Hováth) (Hemiptera: Delphacidae). Due to low virus transmission efficiency by the planthopper, researchers are frequently confronted with shortage of viruliferous vectors or infected rice plants, especially in winter and the following spring. To find new ways to maintain virus-infected materials, viral rice plants were stored at -80°C for 45 or 140 d and evaluated as virus sources in virus transmission by the vector. SRBSDV virions were not degraded during storage at -80°C as indicated by reverse transcription-polymerase chain reaction and reverse transcription real-time PCR detection. The planthopper nymphs fed on the infected thawed plants for 48 h survived at about 40% and showed positive detection of SRBSDV, but they lost the virus after feeding for another 20 d (the circulative transmission period) on noninfected plants. Transmission electron microscope images indicated broken capsid of virions in infected thawed leaves in contrast to integrity capsid of virions in infected fresh leaves. These results show that low temperature storage of SRBSDV-infected rice plants cannot sustain virus transmission by white-backed planthopper.

Reference Gene Selection and Evaluation for Gene Expression Studies Using qRT-PCR in the White-Backed Planthopper, Sogatella furcifera (Hemiptera: Delphacidae).

The white-backed planthopper, Sogatella furcifera (Hemiptera, Delphacidae), is one of the most devastating rice pests. For a better control strategy, various genetic studies have been conducted using reverse-transcription quantitative real-time polymerase chain reaction (qRT-PCR). The appropriate application of qRT-PCR requires reliable endogenous controls; however, studies on this aspect of the white-backed planthopper are lacking. In the present study, nine commonly used reference genes, elongation factor 1-α (EF1-α), polyubiquitin (UB), ribosomal protein S18 (RPS18), actin 1 (ACT), α-1 tubulin (TUB), glyceraldehyde-3-phosphate (GAPDH), ribosomal protein L9 (RPL9), ribosomal protein L10 (RPL10), and 18S ribosomal RNA (18S), were evaluated by qRT-PCR for their expression stability under four different experimental conditions (different developmental stages, acquisition of Southern rice black-streaked dwarf virus (SRBSDV), different tissues, and different temperature stress). These results were analyzed using four software programs (geNorm, NormFinder, BestKeeper, and the delta Ct method) and a Web-based comprehensive tool RefFinder to compare and rank candidate reference genes. According to the results of RefFinder analysis, which integrates the abovementioned four software programs, TUB was ranked as the most suitable reference gene at different developmental stages and under different temperature stress, and GAPDH and RPL9 showed the highest stability for acquisition of SRBSDV and different tissues, respectively. These results will provide a solid foundation for future gene expression study on the white-backed planthopper, and also will give aids in establishing a standardized qRT-PCR procedure for other related insects.

Relation Between the Viral Load Accumulation of Southern Rice Black-Streaked Dwarf Virus and the Different Developmental Stages of Sogatella furcifera (Hemiptera: Delphacidae).

The white-backed planthopper, Sogatella furcifera (Horvath), is currently the only confirmed vector of Southern rice black-streaked dwarf virus (SRBSDV), which causes severe rice production losses in China. In this study, an absolute quantification qPCR method was used to detect viral gene mRNA expression levels at different developmental stages of white-backed planthoppers fed SRBSDV-infected rice plants. A comparison of viral copy numbers of the SRBSDV S10 gene at the same developmental stage indicated that the white-backed planthopper had higher viral copy numbers when the virus was acquired at the earlier developmental stages. The adult-stage white-backed planthoppers that had acquired the virus at the first-second nymphal stage displayed significantly higher viral titers than white-backed planthoppers that acquired the virus at the third-fourth nymphal stage, at the fifth nymphal stage, and at the adult stage. The fifth nymphal stage white-backed planthoppers that acquired the virus at the first-second nymphal stage displayed higher viral copy numbers than fifth nymphal stage white-backed planthoppers that acquired the virus at the third-fourth nymphal stage and at the fifth nymphal stage. The highest viral load value appeared in the middle adult stage. The annual immigration characteristics of white-backed planthoppers would be beneficial for the dispersal of SRBSDV because this virus could be transmitted far away following the migration of vigorous planthoppers. Therefore, investigating the change in the viral load at different life stages of SRBSDV-positive individuals is required to develop more effective control of the spread of SRBSDV in the field.

Toxicity of Insecticides Targeting Rice Planthoppers to Adult and Immature Stages of Trichogramma chilonis (Hymenoptera: Trichogrammatidae).

Planthopper-targeting insecticides, pymetrozine, thiamethoxam, buprofezin, and nitenpyram, were tested under laboratory conditions for toxicity to adults and immatures of Trichogramma chilonis Ishii, using standard tests described by International Organization for Biological Control (IOBC). In the dry film residue test, all insecticides resulted in >90% mortality in T. chilonis adults and were ranked as moderately harmful. Persistent toxicity tests revealed that nitenpyram was short-lived and the other three insecticides were of slightly persistent toxicity to the wasp adults. Effects of the insecticides on egg, larval, and prepupal stages of T. chilonis were investigated with striped stem borer as host. At the three stages of T. chilonis (within the host egg), all the insecticides reduced parasitism rate, but nitenpyram and pymetrozine applied at egg stage, buprofezin and nitenpyram at larval stage, and buprofezin and thiamethoxam at prepupal stage of T. chilonis reduced parasitism by <30% in comparison with the control, and were thus ranked as harmless. Although insecticide treatment of the three immature stages of T. chilonis all reduced wasp emergence from host eggs, only thiamethoxam applied at larval stage and buprofezin at prepupal stage resulted in >30% reduction in emergence rate as compared with the control and were categorized as harmful. Immature duration of T. chilonis was only significantly extended by nitenpyram applied to egg stage than the control. Sex ratio of emerged wasps was not affected by the treatment to immature stages. The data are of significance for IPM programs incorporating inundative release of T. chilonis for control of lepidopteran rice pests where there is heavy co-occurrence of planthoppers.

Binding site concentration explains the differential susceptibility of Chilo suppressalis and Sesamia inferens to Cry1A-producing rice.

Chilo suppressalis and Sesamia inferens are two important lepidopteran rice pests that occur concurrently during outbreaks in paddy fields in the main rice-growing areas of China. Previous and current field tests demonstrate that the transgenic rice line Huahui 1 (HH1) producing a Cry1Ab-Cry1Ac hybrid toxin from the bacterium Bacillus thuringiensis reduces egg and larval densities of C. suppressalis but not of S. inferens. This differential susceptibility to HH1 rice correlates with the reduced susceptibility to Cry1Ab and Cry1Ac toxins in S. inferens larvae compared to C. suppressalis larvae. The goal of this study was to identify the mechanism responsible for this differential susceptibility. In saturation binding assays, both Cry1Ab and Cry1Ac toxins bound with high affinity and in a saturable manner to midgut brush border membrane vesicles (BBMV) from C. suppressalis and S. inferens larvae. While binding affinities were similar, a dramatically lower concentration of Cry1A toxin binding sites was detected for S. inferens BBMV than for C. suppressalis BBMV. In contrast, no significant differences between species were detected for Cry1Ca toxin binding to BBMV. Ligand blotting detected BBMV proteins binding Cry1Ac or Cry1Ca toxins, some of them unique to C. suppressalis or S. inferens. These data support that reduced Cry1A binding site concentration is associated with a lower susceptibility to Cry1A toxins and HH1 rice in S. inferens larvae than in C. suppressalis larvae. Moreover, our data support Cry1Ca as a candidate for pyramiding efforts with Cry1A-producing rice to extend the activity range and durability of this technology against rice stem borers.

Interactive Effects of Southern Rice Black-Streaked Dwarf Virus Infection of Host Plant and Vector on Performance of the Vector, Sogatella furcifera (Homoptera: Delphacidae).

Performance of insect vectors can be influenced by the viruses they transmit, either directly by infection of the vectors or indirectly via infection of the host plants. Southern rice black-streaked dwarf virus (SRBSDV) is a propagative virus transmitted by the white-backed planthopper, Sogatella furcifera (Hovath). To elucidate the influence of SRBSDV on the performance of white-backed planthopper, life parameters of viruliferous and nonviruliferous white-backed planthopper fed rice seedlings infected or noninfected with SRBSDV were measured using a factorial design. Regardless of the infection status of the rice plant host, viruliferous white-backed planthopper nymphs took longer to develop from nymph to adult than did nonviruliferous nymphs. Viruliferous white-backed planthopper females deposited fewer eggs than nonviruliferous females and both viruliferous and nonviruliferous white-backed planthopper females laid fewer eggs on infected than on noninfected plants. Longevity of white-backed planthopper females was also affected by the infection status of the rice plant and white-backed planthopper. Nonviruliferous white-backed planthopper females that fed on infected rice plants lived longer than the other three treatment groups. These results indicate that the performance of white-backed planthopper is affected by SRBSDV either directly (by infection of white-backed planthopper) or indirectly (by infection of rice plant). The extended development of viruliferous nymphs and the prolonged life span of nonviruliferous adults on infected plants may increase their likelihood of transmitting virus, which would increase virus spread.

Evaluation for potential Trichogramma (Hymenoptera: Trichogrammatidae) strains for control of the striped stem borer (Lepidoptera: Crambidae) in the Greater Mekong Subregion.

Trichogramma species and strains differ significantly in host specificity and performance. Nine Trichogramma strains, six of them collected from paddy fields in the Greater Mekong Subregion, were evaluated for performance on eggs of the striped stem borer, Chilo suppressalis (Walker), in both laboratory and field tests to determine potential Trichogramma strains that can be used in an inundative release in an integrated pest management program. In the laboratory glass vial tests, all strains showed higher parasitism rates on 0-24-h eggs than on the two older age groups (24-48 and 48-72 h). Wasp emergence rate was also higher from parasitized 0-24-h striped stem borer eggs, while Trichogramma immature duration was significantly prolonged on 0-24-h striped stem borer eggs. Parasitism rates differed among Trichogramma strains, with Trichogramma chilonis Ishii CJ strain showing significantly higher parasitism rate than any other strains. In the field tests, parasitism of sentinel striped stem borer eggs by Trichogramma strains released at 50,000, 100,000, and 200,000 wasps per hectare was low, with marginal yet significant differences between strains. The highest parasitism was achieved by T. chilonis CJ strain at the high and medium release rates. Hence, it can be concluded that T. chilonis CJ strain released at 100,000 wasps per hectare may be a cost-effective control tactic for field releases targeting striped stem borer.

Sublethal concentrations of pymetrozine reduce Sogatella furcifera transmission of Southern rice black-streaked dwarf virus.

BACKGROUND: The transmission of plant viruses is closely associated with the specific probing behaviors of the vectors. Pymetrozine is a pyridine azomethine insecticide that interferes with nervous regulation of feeding behavior of piercing-sucking insects. This study aimed to evaluate the potential of sublethal concentrations of pymetrozine in reducing the transmission of Southern rice black-streaked dwarf virus (SRBSDV) by the planthopper Sogatella furcifera. RESULTS: Laboratory assays showed that both acquisition and inoculation rates of SRBSDV decreased significantly in the planthoppers feeding on plants treated with lethal concentrations 10% and 50% (LC10 and LC50 ) pymetrozine compared with the insects feeding on the control plants, for which significant effects of pymetrozine concentration and time post-treatment were detected. Honeydew excretion of the planthoppers showed significant reduction with increasing concentration of the insecticide but no significant association with time post-treatment. Electrical penetration graph recordings revealed that total durations of each waveform in both acquisition and inoculation were significantly affected by pymetrozine treatment, with total durations of non-probing (NP), penetration initiation (N1), and extracellular activity (N3) elongated whereas those of salivation (N2) and phloem-related activities (N4-a and N4-b) shortened. Additionally, both acquisition and inoculation rates were significantly lower at 168 h than at 6 h post-treatment. CONCLUSION: The results indicate that sublethal concentrations of pymetrozine reduce SRBSDV transmission, which is associated with reduction in feeding and alteration in probing behaviors characterized by the prolonged non-probing, penetration initiation and extracellular activity and shortened salivation and phloem-related activities. © 2023 Society of Chemical Industry.

Rice varietal resistance to the vector Sogatella furcifera hinders transmission of Southern rice black-streaked dwarf virus.

BACKGROUND: The Southern rice black-streaked dwarf virus (SRBSDV) transmitted by Sogatella furcifera constitutes a threat to sustainable rice production. However, most rice varieties are highly vulnerable to SRBSDV, whereas the occurrence of the viral disease varies significantly under field conditions. This study aimed to evaluate the potential of rice varietal resistance to S. furcifera in reducing SRBSDV transmission. RESULTS: Among the five rice varieties, Zhongzheyou8 and Deyou108 exhibited high resistance to S. furcifera, Baixiangnuo33 was susceptible, and TN1 and Diantun502 were highly susceptible. The S. furcifera generally showed non-preference for and low feeding on the Zhongzheyou8 and Deyou108 plants, which may explain the resistance of these varieties to S. furcifera. Transmission of SRBSDV by S. furcifera was significantly impaired on the resistant varieties, both inoculation and acquisition rates were much lower on Zhongzheyou8 than on TN1. The short durations of S. furcifera salivation and phloem-related activities and the low S. furcifera feeding amount may explain the reduced SRBSDV inoculation and acquisition rates associated with Zhongzheyou8. Spearman's rank correlation revealed a significant negative correlation between S. furcifera resistance and SRBSDV transmission among the tested varieties. CONCLUSION: The results indicate that rice varietal resistance to the vector S. furcifera hinders SRBSDV transmission, which is largely associated with the host plant selection and feeding behaviors of the vector. The current findings shed light on the management of the SRBSDV viral disease through incorporation of S. furcifera resistant rice varieties in the management protocol. © 2024 Society of Chemical Industry.

Predatory Capacity and Reproduction of Cyrtorhinus lividipennis (Hemiptera: Miridae) Adults Exposed to Low-Temperature Storage and Fitness of the F1 Generation.

Low-temperature storage (LTS) is a way to adjust natural enemy development to meet field release needs and to protect natural enemies from the odds of long-distance transportation. The mirid bug Cyrtorhinus lividipennis Reuter (Hemiptera: Miridae) is an important predator of planthoppers and leafhoppers in rice fields. In this study, the LTS effects were measured on the predatory capacity and reproduction of the mirid adults (provided with 20% honey solution and stored at 13 °C for 12 days), and the fitness of the F1 generation of these adults. Higher predation of the eggs of the brown planthopper Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) was observed in the post-storage females than in the control females. The functional responses of C. lividipennis adults, either exposed to LTS or not, to planthopper eggs fitted well with Holling type II functional responses. Longevity was not affected by LTS, whereas the number of offspring nymphs was 55.6% lower in the post-storage females than in the control females. The fitness of the offspring generation was not affected by the LTS of parental adults. The findings are discussed with their relevance to biological control.

Molecular Evolutionary Mechanisms of CYP6ER1vA-Type Variant Associated with Resistance to Neonicotinoid Insecticides in Field Populations of Nilaparvata lugens.

The evolution of insecticide resistance has threatened the control of Nilaparvata lugens. Research on mechanisms behind neonicotinoid resistance in N. lugens remains incomplete. This study examined P450-mediated resistance to neonicotinoids in a resistant N. lugens strain (XA-2017-3G). The overexpression of CYP6ER1 in the XA-2017-3G strain plays a role in neonicotinoid resistance, as confirmed by RNA interference. Phenotypic analyses of CYP6ER1-mediated resistance in strains, including laboratory-susceptible, field-collected, and imidacloprid-laboratory further-selected strains, revealed that the vA-type/vL-type genotype exhibited greater resistance to neonicotinoids compared to the vA-type/vA-type genotype. The mRNA expression levels of CYP6ER1vA-type were closely correlated with the levels of neonicotinoid resistance in N. lugens strains, in which CYP6ER1vA-type overexpression is in part attributed to increased copy numbers of CYP6ER1. CYP6ER1vA-type-mediated neonicotinoid resistance was further confirmed by a CYP6ER1vA-type transgenic Drosophila melanogaster line. Taken together, our findings strongly suggest that the overexpression of CYP6ER1vA-type, which can be partially attributed to copy number variations, plays a crucial role in N. lugens resistance to neonicotinoids.

Lack of Known Target-Site Mutations in Field Populations of Ostrinia furnacalis in China from 2019 to 2021.

The Asian corn borer, Ostrinia furnacalis (Guenée) (Lepidoptera; Pyralidae), is one of the most destructive insect pests of corn, for which chemical insecticides have been the primary method of control, especially during outbreaks. Little information is currently available on the status of insecticide resistance and associated mechanisms in O. furnacalis field populations. Invasions and outbreaks of Spodoptera frugiperda in China in recent years have increased chemical application in corn fields, which adds to the selection pressure on O. furnacalis. This study was conducted to estimate the risk of insecticide resistance by investigating the frequency of insecticide resistant alleles associated with target site insensitivity in field populations of O. furnacalis. Using the individual-PCR genotype sequencing analysis, none of the six target-site insecticide resistant mutations were detected in O. furnacalis field populations collected from 2019 to 2021 in China. These investigated insecticide resistance alleles are common in resistant Lepidoptra pests and are responsible for resistance to pyrethroids, organophosphorus, carbamates, diamide, and Cry1Ab. Our results support the low insecticide resistance status in field O. furnacalis populations and betokens the unlikely development of high resistance mediated by the common target-site resistance alleles. Additionally, the findings would serve as references for further efforts toward the sustainable management of O. furnacalis.

Silencing the Autophagy-Related Genes ATG3 and ATG9 Promotes SRBSDV Propagation and Transmission in Sogatella furcifera.

Autophagy plays diverse roles in the interaction among pathogen, vector, and host. In the plant virus and insect vector system, autophagy can be an antiviral/pro-viral factor to suppress/promote virus propagation and transmission. Here, we report the antiviral role of autophagy-related genes ATG3 and ATG9 in the white-backed planthopper (Sogatella furcifera) during the process of transmitting the southern rice black-streaked dwarf virus (SRBSDV). In this study, we annotated two autophagy-related genes, SfATG3 and SfATG9, from the female S. furcifera transcriptome. The cDNA of SfATG3 and SfATG9 comprised an open reading frame (ORF) of 999 bp and 2295 bp that encodes a protein of 332 and 764 amino acid residues, respectively. SfATG3 has two conserved domains and SfATG9 has one conserved domain. In S. furcifera females exposed to SRBSDV, expression of autophagy-related genes was significantly activated and shared similar temporal patterns to those of SRBSDV S9-1 and S10, all peaking at 4 d post viral exposure. Silencing the expression of SfATG3 and SfATG9 promoted SRBSDV propagation and transmission. This study provides evidence for the first time that S. furcifera autophagy-related genes ATG3 and ATG9 play an antiviral role to suppress SRBSDV propagation and transmission.

Comparison of Transcriptome Responses between Sogatella furcifera Females That Acquired Southern Rice Black-Streaked Dwarf Virus and Not.

The southern rice black-streaked dwarf virus (SRBSDV) is transmitted horizontally by Sogatella furcifera in a persistent, propagative manner. Exposure of S. furcifera females to SRBSDV-infected rice plants may trigger transcriptomic changes in the insects, the transcriptomes of females that acquired SRBSDV and those that failed to, as well as females fed on healthy rice plants as control, were sequenced and compared. Nine transcriptomic libraries were constructed, from which a total of 53,084 genes were assembled. Among the genes, 1043 and 2932 were differentially expressed genes (DEGs) in S. furcifera females that acquired SRBSDV and that failed to, in comparison with the control, respectively. Functional enrichment analysis showed that DEGs identified in S. furcifera females exposed to SRBSDV are primarily involved in diverse signaling pathways related to primary metabolism and innate immunity. The DEGs in the S. furcifera females that failed to acquire the virus significantly outnumbered that in the insects that acquired the virus, and the virus exposure activated the humoral and cellular immune responses of the vectors, especially the apoptosis. The key gene in apoptosis encoding caspase 1 was upregulated by SRBSDV exposure, especially in S. furcifera females that failed to acquire the virus. Analysis of caspase 1 activity validated that SRBSDV exposure induced caspase 1 accumulation. Surprisingly, the expression of six female-specific genes was also upregulated by SRBSDV exposure, which was confirmed by RT-qPCR analysis. This study provides evidence to explain the differential virus acquisition at the transcriptome level.

Identification of Key Headspace Volatile Compounds Signaling Preference for Rice over Corn in Adult Females of the Rice Leaf Folder Cnaphalocrocis medinalis.

Volatile organic compounds are important for herbivorous insects in locating their host plants. The rice leaf folder, Cnaphalocrocis medinalis (Guenée), is a devastating migratory insect pest of rice in Asian countries. Although C. medinalis can develop even better on corn than on rice plants in insectaries, it rarely occurs on corn plants in the field. We hypothesized that plant volatile-mediated oviposition preference for rice over corn in adult females may be the reason for the observed rare field occurrence of the pest on corn plants. The present study was conducted to identify the olfactory active volatile compounds (OAVCs) that enable C. medinalis females to discriminate rice from corn plants. In cage tests, rice plants were highly preferred for oviposition over corn plants by C. medinalis females. From headspace, chemical analyses identified 15 rice unique, 8 corn unique, and 28 common volatile compounds. Fourteen OAVCs, including seven common, five rice unique, and two corn unique, were determined. In electroantennogram tests, the rice unique and common OAVCs activated the antennal responses in C. medinalis. In Y-tube olfactometer tests, (E)-2-hexenal and 3-hexanol(common OAVCs) and (Z)-3-hexenyl acetate and (E)-2-hexen-1-ol (rice unique OAVCs) attracted more C. medinalis females than the control, and only blends with both rice unique and common OAVCs were highly preferred over the control. Our results provide insights into the chemical cues used by C. medinalis adult females in host location, which may aid the development of novel crop protection strategies based on the manipulation of host-finding behaviors of C. medinalis.

Activation of Wheat Defense Response by Buchnera aphidicola-Derived Small Chaperone Protein GroES in Wheat Aphid Saliva.

Salivary proteins secreted by aphids during feeding play an important role in regulating the plant defense response. We used mass spectrometry to identify 155 proteins from the wheat aphid, Sitobion miscanthi, among which 44 proteins were derived from the primary symbiont, Buchnera aphidicola. GroES, which is a highly abundant molecular chaperone that binds to GroEL, was detected in saliva. In vitro injection of purified GroES protein and overexpression of GroES in wheat leaves verified that GroES induced hydrogen peroxide accumulation and callose deposition in wheat and further activated the plant salic acid and jasmonic acid defense pathways. Our findings indicate that plants may have evolved new strategies to detect aphid attack and trigger defense responses by recognizing proteins derived from B. aphidicola, which is present in almost all aphid species.