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Orthotospovirus tomatomaculae (tomato spotted wilt virus, TSWV) is transmitted by the western flower thrips, Frankliniella occidentalis. Epoxyoctadecamonoenoic acids (EpOMEs) function as immune-suppressive factors, particularly in insects infected by viral pathogens. These oxylipins are produced by cytochrome P450 monooxygenases (CYPs) and are degraded by soluble epoxide hydrolase (sEH). In this study, we tested the hypothesis that TSWV modulates the EpOME level in the thrips to suppress antiviral responses and enhance its replication. TSWV infection significantly elevated both 9,10-EpOME and 12,13-EpOME levels. Following TSWV infection, the larvae displayed apoptosis in the midgut along with the upregulated expression of four caspase genes. However, the addition of EpOME to the viral treatment notably reduced apoptosis and downregulated caspase gene expressions, which led to a marked increase in TSWV titers. The CYP and sEH genes of F. occidentalis were identified, and their expression manipulation using RNA interference (RNAi) treatments led to significant alternations in the insect's immune responses and TSWV viral titers. To ascertain which viral factor influences the host EpOME levels, specialized RNAi treatments targeting genes encoded by TSWV were administered to larvae infected with TSWV. These treatments demonstrated that NSS expression is pivotal in manipulating the genes involved in EpOME metabolism. These results indicate that NSs of TSWV are crucially linked with the elevation of host insect EpOME levels and play a key role in suppressing the antiviral responses of F. occidentalis. [ABSTRACT FROM AUTHOR]

The western flower thrips, Frankliniella occidentalis, is a serious pest causing both direct feeding damage and indirect harm by transmitting the tomato spotted wilt virus. A spraying double‐stranded RNA (dsRNA) targeted at the vacuolar‐type ATPase (vATPase) gene was developed and demonstrated high insecticidal activity in the laboratory but less effective in field applications. To improve control efficacy under field conditions, three strategies were explored in this study. First, to identify a more efficient RNA interference (RNAi) target, dsRNA specific to the Snf7 gene was tested alongside dsRNA targeting vATPase, and both were found to be similarly effective in controlling the thrips. Second, to elucidate the factors contributing to dsRNA resistance, dsRNA‐degrading enzymes were annotated and their physiological roles in diminishing RNAi efficacy were investigated. Third, to suppress the dsRNA degradation from the dsRNase activities and protect it in field conditions, the dsRNA was encapsulated with chitosan. This formulation enhanced the dsRNA's resistance to environmental stressors such as ultraviolet light and the digestive enzymes in the thrips' gut. Additionally, the chitosan formulation specifically increased the RNAi efficacy, likely by facilitating more efficient entry into the target cells, thus bolstering the insecticidal activity of the dsRNA. The formulated dsRNA was applied on F. occidentalis infesting the hot peppers in a greenhouse at a concentration of 500 ppm, demonstrating an 82.4% control efficacy compared with 59.2% control efficacy observed with the application of naked dsRNA. This study further demonstrated an enhancement in the spectrum of control by combining dsRNAs specific to three distinct thrips species, while the mixture showed no adverse effects on non‐target insects, such as the lepidopteran Spodoptera exigua. Collectively, these findings reveal that the chitosan formulation of dsRNA not only improves control efficacy under field conditions but also broadens the control spectrum against three different thrips pests. [ABSTRACT FROM AUTHOR]

The transmission of insect-borne viruses involves sophisticated interactions between viruses, host plants, and vectors. Chemical compounds play an important role in these interactions. Several studies reported that the plant virus tomato spotted wilt orthotospovirus (TSWV) increases host plant quality for its vector and benefits the vector thrips Frankliniella occidentalis. However, few studies have investigated the chemical ecology of thrips vectors, TSWV, and host plants. Here, we demonstrated that in TSWV-infected host plant Datura stramonium, (1) F. occidentalis were more attracted to feeding on TSWV-infected D. stramonium; (2) atropine and scopolamine, the main tropane alkaloids in D. stramonium, which are toxic to animals, were down-regulated by TSWV infection of the plant; and (3) F. occidentalis had better biological performance (prolonged adult longevity and increased fecundity, resulting in accelerated population growth) on TSWV-infected D. stramonium than on TSWV non-infected plants. These findings provide in-depth information about the physiological mechanisms responsible for the virus's benefits to its vector by virus infection of plant regulating alkaloid accumulation in the plant. [ABSTRACT FROM AUTHOR]

We evaluated the suppressive effect of prohydrojasmon (PDJ) on Frankliniella occidentalis and tomato spotted wilt virus (TSWV) in chrysanthemums under semi-commercial conditions. The overhead sprinkling of plants with PDJ did not suppress the initial colonization of plants by released adult thrips. However, it significantly reduced subsequent feeding damage on leaves and the reproduction of larval offspring. Rates of 1 and 2 L/m2 of 0.8 mM PDJ equally suppressed F. occidentalis and feeding damage without phytotoxic effects, although 3 L/m2 reduced plant growth. Frequencies of 2 and 3 applications of PDJ at different intervals had similar inhibitory effects on F. occidentalis, suggesting the possibility of low-frequency, labor-saving applications in chrysanthemums. Weekly applications suppressed the occurrence of TSWV transmitted by viruliferous adult thrips dispersed from inoculum sources to a degree consistent with that of feeding damage, so PDJ might inhibit primary infection via disruption of feeding behavior. All our findings suggest that PDJ offers a valuable option for controlling F. occidentalis and orthotospovirus diseases transmitted by it in chrysanthemum production greenhouses. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt orthotospovirus (TSWV) causes substantial economic losses to vegetables and other crops. TSWV is mainly transmitted by thrips in a persistent and proliferative manner, and its most efficient vector is the western flower thrips, Frankliniella occidentalis (Pergande). In moving from the thrips midgut to the salivary glands in preparation for transmission, the virions must overcome multiple barriers. Although several proteins that interact with TSWV in thrips have been characterized, we hypothesized that additional thrips proteins interact with TSWV and facilitate its transmission. In the current study, 67 F. occidentalis proteins that interact with GN (a structural glycoprotein) were identified using a split‐ubiquitin membrane‐based yeast 2‐hybrid (MbY2H) system. Three proteins, apolipoprotein‐D (ApoD), orai‐2‐like (Orai), and obstructor‐E‐like isoform X2 (Obst), were selected for further study based on their high abundance and interaction strength; their interactions with GN were confirmed by MbY2H, yeast β‐galactosidase and luciferase complementation assays. The relative expressions of ApoD and Orai were significantly down‐regulated but that of Obst was significantly up‐regulated in viruliferous thrips. When interfering with Obst in larval stage, the TSWV acquisition rate in 3 independent experiments was significantly decreased by 26%, 40%, and 35%, respectively. In addition, when Obst was silenced in adults, the virus titer was significantly decreased, and the TSWV transmission rate decreased from 66.7% to 31.9% using the leaf disk method and from 86.67% to 43.33% using the living plant method. However, the TSWV acquisition and transmission rates were not affected by interference with the ApoD or Orai gene. The results indicate that Obst may play an important role in TSWV acquisition and transmission in Frankliniella occidentalis. [ABSTRACT FROM AUTHOR]

Simple Summary: Frankliniella occidentalis (Pergande) is an invasive pest of a small size with a high reproduction rate. The main damage caused by F. occidentalis is the transmission of the tomato spotted wilt virus, which has had certain impacts on agriculture in China. In this work, the maximum entropy model (MaxEnt) in the species distribution model was used to predict the suitable existence range of F. occidentalis in China, and areas of three levels, including high-, medium- and low-suitable zones, were obtained. In particular, the trend of the species' future geographical distribution was derived based on the results of future projections. The results show that the areas of high- and low-suitability zones will continue to decrease in the future, and the area of medium-suitability zones will significantly increase. Then, the environmental variables affecting the distribution of the insect were screened, and it was concluded that temperature and precipitation might be the two factors affecting the distribution of this species that are worthy of consideration. This study provides certain references for the future pest control of F. occidentalis. Climate change has a highly significant impact on the distribution of species. As the greenhouse effect intensifies each year, the distribution of organisms responds to this challenge in diverse ways. Therefore, climatic environmental variables are a key entry point for capturing the current and future distribution trends of pests. Frankliniella occidentalis is an invasive pest attested worldwide. Its damage is mainly divided into two aspects, including mechanical damage caused by its feeding and egg laying and the spread of tomato spotted wilt virus (TSWV). TSWV is the most dominant transmitted virulent disease. Moreover, F. occidentalis is the major vector for the transmission of this virus, which poses a grave threat to the yield and survival of our crops. In this study, the distribution pattern of this pest was explored using 19 bioclimatic variables based on the Maxent model. The results indicated that in the future, high-suitability areas of F. occidentalis will be widely distributed in 19 provinces of China, with Hebei, Henan, Shandong, Tianjin and Yunnan being the most abundant. Among the 19 bioclimatic variables, the five variables of annual mean temperature (Bio 1), temperature seasonality (standard deviation × 100) (Bio 4), min temperature of the coldest month (Bio 6), mean temperature of the driest quarter (Bio 9) and precipitation of the coldest quarter (Bio 19) were selected as the key environmental variables affecting the distribution of F. occidentalis. In summary, temperature and precipitation are vital factors for the study of the species' distribution, and this study aims to provide new perspectives for the control of this pest in China. [ABSTRACT FROM AUTHOR]

The interactions between plant viruses and insect vectors are very complex. In recent years, RNA sequencing data have been used to elucidate critical genes of Tomato spotted wilt ortho-tospovirus (TSWV) and Frankliniella occidentalis (F. occidentalis). However, very little is known about the essential genes involved in thrips acquisition and transmission of TSWV. Based on transcriptome data of F. occidentalis infected with TSWV, we verified the complete sequence of the E3 ubiquitin-protein ligase UBR7 gene (UBR7), which is closely related to virus transmission. Additionally, we found that UBR7 belongs to the E3 ubiquitin-protein ligase family that is highly expressed in adulthood in F. occidentalis. UBR7 could interfere with virus replication and thus affect the transmission efficiency of F. occidentalis. With low URB7 expression, TSWV transmission efficiency decreased, while TSWV acquisition efficiency was unaffected. Moreover, the direct interaction between UBR7 and the nucleocapsid (N) protein of TSWV was investigated through surface plasmon resonance and GST pull-down. In conclusion, we found that UBR7 is a crucial protein for TSWV transmission by F. occidentalis, as it directly interacts with TSWV N. This study provides a new direction for developing green pesticides targeting E3 ubiquitin to control TSWV and F. occidentalis. [ABSTRACT FROM AUTHOR]

Background: The western flower thrips Frankliniella occidentalis is an insect pest that damages various crops, including hot peppers. It is a vector of a plant pathogen, tomato spotted wilt virus. To control this pest, chemical insecticides have been used in the past, but the control efficacy is unsatisfactory owing to rapid resistance development by F. occidentalis. Methodology: : This study reports a novel control technology against this insect pest using RNA interference (RNAi) of the vacuolar-type ATPase (vATPase) expression. Eight subunit genes (vATPase-A ∼ vATPase-H) of vATPase were obtained from the F. occidentalis genome and confirmed for their expressions at all developmental stages. Results: Double-stranded RNAs (dsRNAs) specific to the eight subunit genes were fed to larvae and adults, which significantly suppressed the corresponding gene expressions after 24-h feeding treatment. These RNAi treatments resulted in significant mortalities, in which the dsRNA treatments at ∼2,000 ppm specific to vATPase-A or vATPase-B allowed complete control efficacy near 100% mortality in 7 days after treatment. To prevent dsRNA degradation by the digestive proteases during oral feeding, dsRNAs were formulated in a liposome and led to an enhanced mortality of the larvae and adults of F. occidentalis. The dsRNAs were then sprayed at 2,000 ppm on F. occidentalis infesting hot peppers in a greenhouse, which resulted in 53.5–55.9% control efficacy in 7 days after treatment. Even though the vATPases are conserved in different organisms, the dsRNA treatment was relatively safe for non-target insects owing to the presence of mismatch sequences compared to the dsRNA region of F. occidentalis. Conclusion: These results demonstrate the practical feasibility of spraying dsRNA to control F. occidentalis infesting crops. [ABSTRACT FROM AUTHOR]

Insect-vectored plant pathogens are known to alter host-plant quality and associated cues, subsequently affecting the frequency of interactions with vectors and influencing pathogen transmission. It is unknown whether these changes deliver information highly specific to the vector and have evolved as a result of host manipulation or if they are more generalist indicator of plant status. In the current study, the responses of two thrips species, Frankliniella occidentalis Pergande, the vector of the tospovirus Tomato spotted wilt virus (TSWV) and a non-vectoring species, F. tritici Fitch, to pathogen-induced plant volatiles (PIPVs) in tomatoes were investigated. As the two species cohabit, and one is a vector of tospoviruses while the other is not, this system is perfectly suited to investigate the specificity of PIPVs to insect vectors. Both species were exposed to PIPVs of TSWV and the begomovirus Tomato yellow leaf curl virus (TYLCV) transmitted by the sweet potato whitefly, Bemisia tabaci Gennadius. Frankliniella tritici did not respond to PIPVs. F. occidentalis was attracted to both TSWV- and TYLCV-infected plants and showed no preference between plants infected by either virus. Volatiles from TSWV- and TYLCV-infected plants were collected and identified using GC–MS. Principal component analysis showed a clear differentiation between the volatiles of the uninfected and infected tomatoes. There was no differentiation between the volatile profiles of the two virus-infected tomatoes, suggesting that PIPVs may be a by-product of viral infection that elicit a generalist response in F. occidentalis and are likely not the result of host manipulation. [ABSTRACT FROM AUTHOR]

Simple Summary: Tomato spotted wilt virus (TSWV) is a plant virus that causes significant economic loss to high-valued crops, including hot pepper and tomato. It is transmitted by some thrips species, including Frankliniella occidentalis. Thrips obtain TSWV by feeding on infected host plants. The TSWV infects the midgut and then enters the thrips bodies, where the virus translocates to salivary glands for subsequent transmission. Here we assessed the actions of two intestinal proteins, glycoprotein (Fo-GN) and cyclophilin (Fo-Cyp1) in their functional association with TSWV infection of the midgut. Silencing the two genes encoding these two proteins led to a near-zero reduction of TSWV in midguts and salivary glands of the infected thrips. We propose that the two intestinal proteins, Fo-GN and Fo-Cyp1, are TSWV entry targets that are necessary to infect F. occidentalis for continued transmission to additional host plants. Tomato spotted wilt virus (TSWV) is a plant virus that causes massive economic damage to high-valued crops. This virus is transmitted by specific thrips, including the western flower thrips, Frankliniella occidentalis. TSWV is acquired by the young larvae during feeding on infected host plants. TSWV infects the gut epithelium through hypothetical receptor(s) and multiplies within the cells for subsequent horizontal transmission to other plant hosts via the salivary glands during feeding. Two alimentary canal proteins, glycoprotein (Fo-GN) and cyclophilin (Fo-Cyp1), are thought to be associated with the TSWV entry into the gut epithelium of F. occidentalis. Fo-GN possesses a chitin-binding domain, and its transcript was localized on the larval gut epithelium by fluorescence in situ hybridization (FISH) analysis. Phylogenetic analysis indicated that F. occidentalis encodes six cyclophilins, in which Fo-Cyp1 is closely related to a human cyclophilin A, an immune modulator. The Fo-Cyp1 transcript was also detected in the larval gut epithelium. Expression of these two genes was suppressed by feeding their cognate RNA interference (RNAi) to young larvae. The RNAi efficiencies were confirmed by the disappearance of the target gene transcripts from the gut epithelium by FISH analyses. The RNAi treatments directed to Fo-GN or Fo-Cyp1 prevented the typical TSWV titer increase after the virus feeding, compared to control RNAi treatment. Our immunofluorescence assay using a specific antibody to TSWV documented the reduction of TSWV in the larval gut and adult salivary gland after the RNAi treatments. These results support our hypothesis that the candidate proteins Fo-GN and Fo-Cyp1 act in TSWV entry and multiplication in F. occidentalis. [ABSTRACT FROM AUTHOR]

[Objectives] To determine the influence of tomato spotted wilt orthotospovirus (TSWV) on the parthenogenetic reproduction of Frankliniella occidentalis, and investigate how TSWV modulates host plant nutrition to regulate the development and reproductive capacity of these thrips. [Methods] The parthenogenetic fecundity of F. occidentalis that fed on either TSWV-infected, or uninfected, Datura stramonium leaves, were compared. The nutrient content of infected D. stramonium was determined using biochemical methods and the effects of adding amino acids to the growth and fecundity of F. occidentalis were determined. [Results] The parthenogenetic fecundity of F. occidentalis that fed on infected leaves was significantly (1.5 times) higher than that of the control group. The total free amino acid and soluble protein content of infected D. stramonium plants were 1.3 and 3.0 times higher, respectively, than those of uninfected plants. The nymphal development of F. occidentalis fed on leaf disks supplemented with amino acids was significantly accelerated by 0.3 d, and offspring numbers produced by sexual and parthenogenetic reproduction were 50% (P<0.01) and 60% (P<0.01) higher, respectively, than those of the control group. [Conclusion] TSWV infection increases the total free amino acid content of D. stramonium, which appears to benefit the development and reproduction of F. occidentalis. [ABSTRACT FROM AUTHOR]

Western flower thrips (Frankliniella occidentalis) are among the most important pests globally that transmit destructive plant viruses and infest multiple commercial crops. Lysine lactylation (Klac) is a recently discovered novel post-translational modification (PTM). We used liquid chromatography-mass spectrometry to identify the global lactylated proteome of F. occidentalis, and further enriched the identified lactylated proteins using Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO). In the present study, we identified 1,458 Klac sites in 469 proteins from F. occidentalis. Bioinformatics analysis showed that Klac was widely distributed in F. occidentalis proteins, and these Klac modified proteins participated in multiple biological processes. GO and KEGG enrichment analysis revealed that Klac proteins were significantly enriched in multiple cellular compartments and metabolic pathways, such as the ribosome and carbon metabolism pathways. Two Klac proteins were found to be involved in the regulation of the TSWV (Tomato spotted wilt virus) transmission in F. occidentalis. This study provides a systematic report and a rich dataset of lactylation in F. occidentalis proteome for potential studies on the Klac protein of this notorious pest. [ABSTRACT FROM AUTHOR]

BACKGROUND: Plant viruses can facilitate their transmission by modulating the sex ratios of their insect vectors. Previously, we found that exposure to tomato spotted wilt orthotospovirus (TSWV) in the western flower thrips, Frankliniella occidentalis, led to a male‐biased sex ratio in the offspring. TSWV, a generalist pathogen with a broad host range, is transmitted primarily by F. occidentalis in a circulative‐propagative manner. Here, we integrated proteomic tools with RNAi to comprehensively investigate the genetic basis underlying the shift in vector sex ratio induced by the virus. RESULTS: Proteomic analysis exhibited 104 differentially expressed proteins between F. occidentalis adult males with and without TSWV. The expression of the fiber sheath CABYR‐binding‐like (FSCB) protein, namely FoFSCB‐like, a sperm‐specific protein associated with sperm capacitation and motility, was decreased by 46%. The predicted FoFSCB‐like protein includes 10 classic Pro‐X‐X‐Pro motifs and 42 phosphorylation sites, which are key features for sperm capacitation. FoFSCB‐like expression was gradually increased during the development and peaked at the pupal stage. After exposure to TSWV, FoFSCB‐like expression was substantially down‐regulated. Nanoparticle‐mediated RNAi substantially suppressed FoFSCB‐like expression and led to a significant male bias in the offspring. CONCLUSION: These combined results suggest that down‐regulation of FoFSCB‐like in virus‐exposed thrips leads to a male‐biased sex ratio in the offspring. This study not only advances our understanding of virus‐vector interactions, but also identifies a potential target for the genetic management of F. occidentalis, the primary vector of TSWV, by manipulating male fertility. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The excessive use of chemical products to control thrips and the tomato spotted wilt virus (TSWV) is not only harmful to human health, the environment, and biodiversity, but also the resistance these generate in insects turns them inefficient in the long run. Consequently, to achieve sustainable and residue-free production, control alternatives must be explored. This work proposes the use of Beauveria bassiana (BB) in combination with inter-row cover (IC) to reduce the population of thrips and the incidence of TSWV on bell pepper. For this purpose, a trial was carried out in a bell pepper greenhouse, consisting of four randomly distributed treatments with four repetitions of 66 plants each. The treatments assayed were: T (without BB inoculation or IC), TC (without BB inoculation and with IC), B (inoculated with BB), and BC (inoculated with BB and IC). The B. bassiana CEP147 strain was used based on its effectiveness in previous laboratory tests. After detecting one thrips per flower, five foliar spray applications were made at weekly intervals. The trial lasted 4 months. During this time, the number of thrips in the three central plants of each repetition, the presence of symptoms compatible with TSWV, as well as the number of fruits, and their weight, length, width and health were monitored weekly. Between the fourth and sixth weeks after the last application, a significant reduction in the population of total thrips (nymphs + + adults) was observed in both treatments B and BC compared to T and TC. In addition, plants with symptoms compatible with TSWV were very scarce, and the fruits showed significant differences in their quality parameters, producing the longest and heaviest in the BC treatment. The results showed that combining biological and cultural control makes sustainable pepper production possible. [ABSTRACT FROM AUTHOR]

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) is an important pest that transmits tospoviruses such as Tomato spotted wilt virus. Jasmonate (JA) and its derivatives are phytohormones with essential roles in plant defense against herbivorous arthropods. In experiments conducted over 2 years, we evaluated how spraying with prohydrojasmon (PDJ), a JA derivative, affected F. occidentalis infestations of greenhouse-grown tomato plants. Single or consecutive sprayings of 400 nmol/mL PDJ in the early plant growth stage significantly suppressed thrips infestation and feeding damage as well as spinetoram. Although spraying with PDJ slightly inhibited initial plant growth, fruit yields and quality were not affected. These results suggest that PDJ could be practically used as a repellent to control F. occidentalis infestation and primary tospovirus infection in commercial tomato greenhouses. [ABSTRACT FROM AUTHOR]

Western flower thrips, Frankliella occidentalis , is a serious pest by directly infesting host crops. It can also give indirect damage to host crops by transmitting a plant virus called tomato spotted wilt virus. A fungal pathogen, Beauveria bassiana , can infect thrips. It has been used as a biopesticide. However, little is known on the defense of thrips against this fungal pathogen. This study assessed the defense of thrips against the fungal infection with respect to immunity by analyzing immune-associated genes of F. occidentalis in both larvae and adults. Immunity-associated genes of western flower thrips were selected from three immunity steps: nonself recognition, mediation, and immune responses. For the pathogen recognition step, dorsal switch protein 1 (DSP1) was chosen. For the immune mediation step, phospholipase A2 (PLA2) and prostaglandin E2 synthase were also selected. For the step of immune responses, two phenoloxidases (PO) genes and four proPO-activating peptidase genes involved in melanization against pathogens were chosen. Dual oxidase gene involved in the production of reactive oxygen species and four antimicrobial peptide genes for executing humoral immune responses were selected. All immunity-associated genes were inducible to the fungal infection. Their expression levels were induced higher in adults than in larvae by the fungal infections. However, inhibitor treatments specific to DSP1 or PLA2 significantly suppressed the inducible expression of these immune-associated genes, leading to significant enhancement of fungal pathogenicity. These results suggest that immunity is essential for thrips to defend against B. bassiana , in which DSP1 and eicosanoids play a crucial role in eliciting immune responses. [ABSTRACT FROM AUTHOR]

Background: The gut is the first barrier to infection by viruses that are internally borne and transmitted persistently by arthropod vectors to plant and animal hosts. Tomato spotted wilt virus (TSWV), a plant-pathogenic virus, is transmitted exclusively by thrips vectors in a circulative-propagative manner. Frankliniella occidentalis (western flower thrips), the principal thrips vector of TSWV, is transmission-competent only if the virus is acquired by young larvae. To begin to understand the larval gut response to TSWV infection and accumulation, a genome-assisted, transcriptomic analysis of F. occidentalis gut tissues of first (early L1) and second (early L2 and late L2) instar larvae was conducted using RNA-Seq to identify differentially-expressed transcripts (DETs) in response to TSWV compared to non-exposed cohorts. Results: The larval gut responded in a developmental stage-dependent manner, with the majority of DETs (71%) associated with the early L1 stage at a time when virus infection is limited to the midgut epithelium. Provisional annotations of these DETs inferred roles in digestion and absorption, insect innate immunity, and detoxification. Weighted gene co-expression network analysis using all assembled transcripts of the gut transcriptome revealed eight gene modules that distinguish larval development. Intra-module interaction network analysis of the three most DET-enriched modules revealed ten central hub genes. Droplet digital PCR-expression analyses of select network hub and connecting genes revealed temporal changes in gut expression during and post exposure to TSWV. Conclusions: These findings expand our understanding of the developmentally-mediated interaction between thrips vectors and orthotospoviruses, and provide opportunities for probing pathways for biomarkers of thrips vector competence. [ABSTRACT FROM AUTHOR]

As one of the top 10 plant viruses, the severity of losses to crop productivity caused by the tomato spotted wilt virus (TSWV) has resulted in an urgent need to develop a more sensitive and rapid method of detection. In this study, we developed a CRISPR/Cas13a-based detection system to diagnose TSWV in tomato and western flower thrips (Frankliniella occidentalis). The detection system relies on recombinase polymerase amplification and Cas13a-mediated collateral cleavage activity. Positive results can be distinguished after 20 min by a significantly enhanced fluorescence signal. We tested the sensitivity of CRISPR/Cas13a-based detection system and found that the detection system that we developed has limits of detection that reaches 2.26 × 102 copies/μl and a 10-fold increase compared with the sensitivity of using RT-PCR to detect the virus. Furthermore, the CRISPR/Cas13a-based detection system has a high selectivity for the TSWV without interference from other viruses. The CRISPR/Cas13a-based detection system was utilized to detect the TSWV in samples of tomato leaves and the transmission vector F. occidentalis that were fully consistent with the results when RT-PCR was used to detect the virus. Schematic of CRISPR/Cas13-based virus detection. [ABSTRACT FROM AUTHOR]

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), is an important, worldwide vector of two tospoviruses (Family Bunyaviridae; Genus Tospovirus), Impatiens necrotic spot virus (INSV) and Tomato spotted wilt virus (TSWV). In the Salinas Valley of California, INSV causes severe necrosis, stunting, and crop losses to lettuce (Lactuca sativa L.). Because broccoli (Brassica oleracea var. italica L.) and cauliflower (Brassica oleracea var. botrytis L.) are major rotation crops with lettuce in the Salinas Valley, it is critical to understand if these Brassicas influence the dispersal dynamics of F. occidentalis. In 2013 and 2014, surveys were conducted evaluating yellow sticky cards and plant samples in lettuce, broccoli, and cauliflower fields in three regions of the Salinas Valley. F. occidentalis were collected on sticky cards from April to November and on foliage in all three regions. Two-choice oviposition assays as well as no-choice and two-choice feeding assays were conducted where F. occidentalis adults were exposed to leaves of lettuce, broccoli, and cauliflower. A significantly greater number of eggs was found on lettuce than on broccoli or cauliflower leaves in the choice assay, whereas for the broccoli and cauliflower choice assay, the number of eggs retrieved was low and not significantly different between hosts. The number of F. occidentalis feeding spots and leaf area injury ratings were similar on broccoli and lettuce leaves but were significantly lower on cauliflower than on lettuce and broccoli leaves. The implications of these results on thrips and plant virus management are discussed. [ABSTRACT FROM AUTHOR]

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The western flower thrips, Frankliniella occidentalis, is the most efficient vector for Tomato spotted wilt orthotospovirus (TSWV), a devastating plant pathogen. Insecticide resistance is a common issue in pest management. The interactions between insecticide resistance in insect vector and the transmission of plant pathogen, however, are largely unknown. In this study, we assessed the effects of spinosad resistance on TSWV transmission using a pair of near-isogenic lines of susceptible (Ivf03) and resistant (NIL-R) F. occidentalis. NIL-R had a prolonged pre-adult stage, but a shorter adult life span than Ivf03. More importantly, the pupation rate and sex ratio (female/male) in NIL-R were significantly reduced in comparison with Ivf03. When given a shorter acquisition access period (AAP) of 6 h, virus propagation and transmission efficiency in NIL-R were significantly higher than Ivf03. In contrast, a longer AAP of 96 h led to a similar virus acquisition and transmission efficiency for both strains, although TSWV replication was greater in NIL-R. Our combined results suggest that (1) substantial fitness costs (e.g., reduced pupation rate) are associated with spinosad resistance in F. occidentalis; however, (2) insecticide resistance increases vector competence. [ABSTRACT FROM AUTHOR]

Several plant viruses modulate vector fitness and behavior in ways that may enhance virus transmission. Previous studies have documented indirect, plant-mediated effects of tomato spotted wilt virus (TSWV) infection on the fecundity, growth and survival of its principal thrips vector, Frankliniella occidentalis , the western flower thrips. We conducted thrips performance and preference experiments combined with plant gene expression, phytohormone and total free amino acid analyses to determine if systemically-infected tomato plants modulate primary metabolic and defense-related pathways to culminate into a more favorable environment for the vector. In a greenhouse setting, we documented a significant increase in the number of offspring produced by F. occidentalis on TSWV-infected tomato plants compared to mock-inoculated plants, and in choice test assays, females exhibited enhanced settling on TSWV-infected leaves. Microarray analysis combined with phytohormone signaling pathway analysis revealed reciprocal modulation of key phytohormone pathways under dual attack, possibly indicating a coordinated and dampening defense against the vector on infected plants. TSWV infection, alone or in combination with thrips, suppressed genes associated with photosynthesis and chloroplast function thereby significantly impacting primary metabolism of the host plant, and hierarchical cluster and network analyses revealed that many of these genes were co-regulated with phytohormone defense signaling genes. TSWV infection increased expression of genes related to protein synthesis and degradation which was reflected in the increased total free amino acid content in virus-infected plants that harbored higher thrips populations. These results suggest coordinated gene networks that regulate plant primary metabolism and defense responses rendering virus-infected plants more conducive for vector colonization, an outcome that is potentially beneficial to the vector and the virus when considered within the context of the complex transmission biology of TSWV. To our knowledge this is the first study to identify global transcriptional networks that underlie the TSWV-thrips interaction as compared to a single mechanistic approach. Findings of this study increase our fundamental knowledge of host plant-virus-vector interactions and identifies underlying mechanisms of induced host susceptibility to the insect vector. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt orthotospovirus (TSWV) causes serious crop losses worldwide and is transmitted by Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). NSs protein is the silencing suppressor of TSWV and plays an important role in virus infection, cycling, and transmission process. In this research, we investigated the influences of NSs protein on the interaction of TSWV, plants, and F. occidentalis with the transgenic Arabidopsis thaliana. Compared with the wild-type Col-0 plant, F. occidentalis showed an increased number and induced feeding behavior on transgenic Arabidopsis thaliana expressing exogenous NSs. Further analysis showed that NSs reduced the expression of terpenoids synthesis-related genes and the content of monoterpene volatiles in Arabidopsis. These monoterpene volatiles played a repellent role in respect to F. occidentalis. In addition, the expression level of plant immune-related genes and the content of the plant resistance hormone jasmonic acid (JA) in transgenic Arabidopsis were reduced. The silencing suppressor of TSWV NSs alters the emission of plant volatiles and reduces the JA-regulated plant defenses, resulting in enhanced attractiveness of plants to F. occidentalis and may increase the transmission probability of TSWV. [ABSTRACT FROM AUTHOR]

Thrips are a worldwide threat to Capsicum because they damage fruits, flowers and leaves directly by feeding, and indirectly by vectoring tospoviruses such as tomato spotted wilt virus. Therefore, growers would benefit from thrips-resistant varieties. Previously, a quantitative trait locus (QTL) that provides resistance to Frankliniella occidentalis has been identified. Here we explore the potential of this QTL for breeding thrips-resistant varieties by studying its effect on two thrips species (i.e. F. occidentalis and Thrips tabaci) in four different Capsicum annuum backgrounds. We observed differences in thrips resistance between different genetic backgrounds, both in plants that have the resistance allele for the QTL region in homozygous state as well as in plants with the susceptibility allele in homozygous state. This suggests the presence of factors in these backgrounds that either increase or reduce thrips resistance. Altogether, we confirmed the major effect of the QTL on thrips resistance in all four genetic backgrounds to both F. occidentalis and T. tabaci, thus showing its general applicability as a source for breeding thrips-resistant Capsicum varieties. [ABSTRACT FROM AUTHOR]

BACKGROUND: Tomato spotted wilt orthotospovirus (TSWV), one of the most devastating viruses of ornamental plants and vegetable crops worldwide, is transmitted by the western flower thrips, Frankliniella occidentalis (Pergande), in a persistent‐propagative manner. How TSWV influences the reproduction of its vector to enhance transmission and whether infection with TSWV changes the mating behavior of F. occidentalis are not fully understood. RESULTS: TSWV‐exposed thrips had a significantly longer developmental time than non‐exposed individuals. More importantly, increased developmental time was predominantly associated with adults, a stage critical for dispersal and virus transmission. In addition, TSWV‐exposed F. occidentalis produced substantially more progeny than did non‐exposed thrips. Interestingly, most of the increase in progeny came from an increase in males, a sex with a greater dispersal and virus transmission capability. Specifically, the female/male ratio of progeny shifted from 1.3–7.0/1 to 0.6–1.1/1. As for mating behavior, copulation time was significantly longer in TSWV‐exposed thrips. Finally, females tended to re‐mate less when exposed to the virus. Resistance to re‐mating may lead to reduced sperm availability in females, which translates to a larger number of male progeny under a haplodiploid system. CONCLUSION: These combined results suggest that TSWV can influence the developmental time, mating behavior, fecundity, and offspring sex allocation of its vector F. occidentalis to facilitate virus transmission. As such, a monitoring program capable of the earlier detection of the virus in host plants and/or its insect vector, thrips, using double‐antibody sandwich enzyme‐linked immunosorbent assay (DAS‐ELISA), real time quantitative polymerase chain reaction (RT‐qPCR) or virus detection strips might be beneficial for long‐term, sustainable management. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Tomato spotted wilt orthotospovirus (TSWV) is a major disease in peanut, Arachis hypogaea L. across peanut producing regions of the United States and elsewhere. Two thrips, Frankliniella fusca Hinds and Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), are considered important vectors of TSWV in peanut in the Southeast. We compared the efficiency of acquisition (by larvae) and transmission (adults) of both thrips species for TSWV (Texas peanut-strain) to leaf disks of peanut (Florunner), as well as to Impatiens walleriana Hook. f. (Dwarf White Baby) and Petunia hybrida Juss. 'Fire Chief' using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Both species were competent TSWV vectors in peanut and Impatiens, although F. fusca was the more efficient vector overall, i.e. virus acquisition and transmission rates for F. fusca averaged over several bioassays were 51.7 and 26.6%, respectively, compared with 20.0 and 15.3% for F. occidentalis. Neither species effectively transmitted this TSWV strain to Petunia (i.e. ≤3.6% transmission). We found statistically similar virus acquisition and transmission rates between both sexes for each species. We also detected no differences in TSWV-acquisition and transmission frequency between macropterous and brachypterous (short-wing) forms of F. fusca collected from a field population in south Texas. DAS-ELISA failed to detect low levels of TSWV in a few thrips that subsequently proved to be competent vectors. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt is a major disease of crops worldwide. Resistant cultivars carrying the Sw-5 allele for resistance to tomato spotted wilt disease (TSW) provide the most effective control method in tomato (Solanum lycopersicum). However, infections of fruit on Sw-5+ tomato plants suggest the virus resistance may not be fully expressed in blossoms or developing fruit. The objective of this study was to determine if the thrips vector, the western flower thrips (Frankliniella occidentalis), can transmit non-resistance breaking Tomato spotted wilt virus (TSWV) isolates when confined to blossoms on plants with and without the Sw-5 resistance allele. Twenty-one percent of 33 Sw-5+ plants inoculated by adult thrips feeding on blossom clusters or small fruit developed infections in the reproductive tissue, whereas 68% of 25 Sw-5- plants developed infections. Systemic infections also occurred following inoculation of blossoms in host genotypes with and without Sw-5. These results were further supported by field experiments that showed high proportions of infected fruit as well as a limited infection of foliage on the same stem as the infected fruit in Sw-5+ plants when F. occidentalis were abundant in blossoms. These findings help to explain observations of abundant late season infections of Sw-5 cultivars in commercial plantings and suggest that management of F. occidentalis infestations during the bloom period may be important for effective management of TSWV in susceptible tomato cultivars as well as cultivars expressing the Sw-5 allele for TSW resistance. [ABSTRACT FROM AUTHOR]

ABSTRACT The nature of spatial and temporal dynamics of Tomato spotted wilt virus (TSWV) and its vector in a potato crop cv. Innovator without insecticide application is analysed. Seed tuber was analysed for the presence of TSWV as a source of initial inoculum. The presence of plants with symptoms of TSWV was evaluated by visual observation and DAS-ELISA analysis to confirm the virus infection. Thrips species were collected from leaves and inflorescences and identified under stereomicroscope. The distribution of symptomatic plants and thrips species was recorded five times at 14 days intervals. The initial seed tuber infection was of 1.1%. Disease incidence was 0% at 29 days after planting ( DAP), 0.2% at 43 DAP, 2.2% at 56 DAP, 11.6% at 70 DAP and 14.6% at 84 DAP. The progress of the disease was adequately described by a Logistic model [ y = 0.15/(1 + 1205372.93 × exp (−0.22 × DAP))]. Thrips vector species identified as resident in the crop during the whole cycle were Thrips tabaci ( n = 423), Frankliniella occidentalis ( n = 141) and as occasional species, F. schultzei ( n = 34) and F. gemina ( n = 5) were found. At 43 and 56 DAP a random distribution pattern was observed and the thrips species found were T. tabaci ( n = 188) and F. occidentalis ( n = 105). An aggregated pattern was determined at 70 and 84 DAP. Spatial patterns of the disease spread suggest a polycyclic epidemic with TSWV secondary spread in the potato crop. Multiple control measures were deduced from these epidemiological results like virus testing in tubers, removal of external virus infection sources and thrips control. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt virus (TSWV) causes a serious plant disease and is transmitted by specific thrips including the western flower thrips, Frankliniella occidentalis. The persistent and circulative virus transmission suggests an induction of immune defenses in the thrips. We investigated the immune responses of F. occidentalis to TSWV infection. Immunofluorescence assay demonstrated viral infection in the larval midguts at early stage and subsequent propagation to the salivary gland in adults. In the larval midgut, TSWV infection led to the release of DSP1, a damage-associated molecular pattern, from the gut epithelium into the hemolymph. DSP1 up-regulated PLA 2 activity, which would lead to biosynthesis of eicosanoids that activate cellular and humoral immune responses. Phenoloxidase (PO) activity was enhanced following induction of PO and its activating protease gene expressions. Antimicrobial peptide genes and dual oxidase , which produces reactive oxygen species, were induced by the viral infection. Expression of four caspase genes increased and TUNEL assay confirmed apoptosis in the larval midgut after the virus infection. These immune responses to viral infection were significantly suppressed by the inhibition of DSP1 release. We infer that TSWV infection induces F. occidentalis immune responses, which are activated by the release of DSP1 from the infection foci within midguts. [Display omitted] • TSWV infection induces DSP1 release from gut to hemocoel in F. occidentalis. • DSP1 is a damage signal to activate PLA 2 to produce eicosanoids. • Eicosanoids mediate cellular and humoral immune responses of F. occidentalis. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt tospovirus (TSWV), a type species of the genus Orthotospovirus, which belongs to the family Tospoviridae, causes necrotic yellow and necrosis diseases of vegetables including tomatoes and green peppers, and to flowers such as chrysanthemum and dahlia, and causes economic damage, yield loss, and loss of quality. TSWV has a spherical enveloped virion that contains three species of singlestrand RNA segments (L, M, and S). The genome encodes fives genes; a putative cell-to-cell movement protein (NSm), a non-structural protein (NSs), a nucleocapsid protein (N), an RNA-dependent RNA polymerase, and a precursor of surface glycoproteins (GN/GC). TSWV is transmitted in a circulative and propagative manner by thrips such as western flower thrips (Frankliniella occidentalis) and onion thrips (Thrips tabaci). TSWV has been controlled using the virus resistance genes of the cultivars and by controlling the vector using insecticides. However, the emergence of TSWV that can no longer be controlled using the resistance gene of the cultivars and the development of resistance to insecticides by thrips is a serious problem worldwide. Hence, the interactions among TSWV, western flower thrips, and Arabisopsis thaliana were analysed to develop a novel way to control TSWV on the basis of the interaction mechanism. [ABSTRACT FROM AUTHOR]

The article offers information on a research on reverse transcriptase polymerase chain reaction tool for tomato spotted wilt virus detection in its vectors Thrips tabaci and Frankliniella occidentalis. Topics discussed include rearing of larvae of the tobacco-associated onion thrips in early larval stages on leaf disks of infected Nicotiana species; isolation of RNA from infected pepper leaves by the Nucleospin RNA Plant kit and thrips RNA was obtained by TRIZOL method.

Tomato spotted wilt virus (TSWV) is transmitted by Frankliniella occidentalis in a circulative-propagative manner. Little is known about thrips vector response to TSWV during the infection process from larval acquisition to adult inoculation of plants. Whole-body transcriptome response to virus infection was determined for first-instar larval, pre-pupal and adult thrips using RNA-Seq. TSWV responsive genes were identified using preliminary sequence of a draft genome of F. occidentalis as a reference and three developmental-stage transcriptomes were assembled. Processes and functions associated with host defense, insect cuticle structure and development, metabolism and transport were perturbed by TSWV infection as inferred by ontologies of responsive genes. The repertoire of genes responsive to TSWV varied between developmental stages, possibly reflecting the link between thrips development and the virus dissemination route in the vector. This study provides the foundation for exploration of tissue-specific expression in response to TSWV and functional analysis of thrips gene function. [ABSTRACT FROM AUTHOR]

Earlier studies have shown that Tomato spotted wilt virus (TSWV) influences the biology, performance, and behavioral patterns of its vector Frankliniella occidentalis Pergande. In this study, using Capsicum annuum L. as the host plant, we aimed to determine the manipulation of F. occidentalis by TSWV through switching of the diet (+ or -TSWV) during vector's development. Behavioral patterns, fitness, as well as vector performance were evaluated. The specific parameters investigated included longevity/survival, fecundity, development time, feeding, and preferential behavior. F. occidentalis were reared on either TSWV-infected (exposed) or healthy leaves (non-exposed) throughout their larval stages. The emerging adults were then individually transferred to either healthy or TSWV-infected leaf disks. This resulted into four treatments, consisting of exposed or non-exposed thrips reared on either infected or healthy leaf disks as adults. All F. occidentalis exposed to TSWV in their larval stages had shorter development time regardless of the adults' diet. Whereas, the ones that were later reared on healthy leaf disks as adults recorded the highest longevity and reproduction rate. Furthermore, adults of F. occidentalis that were exposed to TSWV in their larval stages showed preference toward healthy leaf disks (-TSWV), whereas the non-exposed significantly preferred the infected leaf disks (+TSWV). These are further indications that TSWV modifies the nutritional content of its host plants, which influences vector's biology and preferential behavior, in favor of its multiplication and dispersal. The findings offer additional explanation to the often aggressive spread of the virus in crop stands. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt virus ( TSWV) is an important plant virus that infects a wide range of hosts including weeds making its management difficult. A survey was undertaken to establish the occurrence of weed species in tomato production systems in Kenya and their role as hosts of TSWV and its vectors. Selected weed species were further evaluated for their reaction to TSWV, transmission efficiency by Frankliniella occidentalis and ability to support thrips reproduction. Of the 43 weed species identified in the field, 29 species had been reported as hosts of TSWV, two were non-hosts and 11 had no record of their status. Among the more common species, Amaranthus hybridus, Solanum nigrum, Tagetes minuta and Datura stramonium were susceptible to the virus and supported high levels of thrips reproduction. The TSWV could not be transmitted to Galinsoga parviflora and Sonchus oleraceus by F. occidentalis despite them being highly susceptible in mechanical transmission tests. There was a significant correlation between feeding damage and number of larvae of F. occidentalis on different weeds. Occurrence of weeds that support thrips reproduction and are good hosts of TSWV is a clear indicator of their role in epidemiology and the importance of their management for disease control. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt virus (TSWV) is transmitted by thrips in a propagative manner; however, progression of virus infection in the insect is not fully understood. The goal of this work was to study the morphology and infection of thrips salivary glands. The primary salivary glands (PSG) are complex, with three distinct regions that may have unique functions. Analysis of TSWV progression in thrips revealed the presence of viral proteins in the foregut, midgut, ligaments, tubular salivary glands (TSG), and efferent duct and filament structures connecting the TSG and PSG of first and second instar larvae. The primary site of virus infection shifted from the midgut and TSG in the larvae to the PSG in adults, suggesting that tissue tropism changes with insect development. TSG infection was detected in advance of PSG infection. These findings support the hypothesis that the TSG are involved in trafficking of TSWV to the PSG. [ABSTRACT FROM AUTHOR]

Several models have been studied on predictive epidemics of arthropod vectored plant viruses in an attempt to bring understanding to the complex but specific relationship between the three cornered pathosystem (virus, vector and host plant), as well as their interactions with the environment. A large body of studies mainly focuses on weather based models as management tool for monitoring pests and diseases, with very few incorporating the contribution of vector’s life processes in the disease dynamics, which is an essential aspect when mitigating virus incidences in a crop stand. In this study, we hypothesized that the multiplication and spread of tomato spotted wilt virus (TSWV) in a crop stand is strongly related to its influences on Frankliniella occidentalis preferential behavior and life expectancy. Model dynamics of important aspects in disease development within TSWV-F. occidentalis-host plant interactions were developed, focusing on F. occidentalis’ life processes as influenced by TSWV. The results show that the influence of TSWV on F. occidentalis preferential behaviour leads to an estimated increase in relative acquisition rate of the virus, and up to 33% increase in transmission rate to healthy plants. Also, increased life expectancy; which relates to improved fitness, is dependent on the virus induced preferential behaviour, consequently promoting multiplication and spread of the virus in a crop stand. The development of vector–based models could further help in elucidating the role of tri-trophic interactions in agricultural disease systems. Use of the model to examine the components of the disease process could also boost our understanding on how specific epidemiological characteristics interact to cause diseases in crops. With this level of understanding we can efficiently develop more precise control strategies for the virus and the vector. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt virus (TSWV) is transmitted by Frankliniella occidentalis (Pergande) in a persistent-propagative manner. We previously observed significant results in terms of feeding behavior of spinosad-susceptible (Ivf03) and -resistant (Spin-R) strains of F. occidentalis using electrical penetration graph. TSWV transmission by the two strains was compared in the present study. The results showed that the titer of TSWV-N RNA (a part of S RNA of TSWV and encoding the nucleocapsid protein) in Ivf03 and Spin-R strains was not significantly different after a 48-h inoculation access period. The TSWV transmission rate did not significantly differ between the two strains and was 51.0% for Ivf03 and 44.4% for Spin-R. The virus transmission rate was significantly higher for males than females of both strains. The virus transmission rate for males and females of Ivf03 was 68.1 and 33.8%, respectively; however, in case of Spin-R, it was 60 and 28.8% for males and females, respectively. Additionally, number of probes and duration of probes were generally greater for viruliferous females of Ivf03 than for viruliferous females of Spin-R but the total number and duration of noningestion probes did not significantly differ between males of the two strains. The latter finding behavior may help explain the similar transmission rates for the susceptible and resistant strains. [ABSTRACT FROM AUTHOR]

The tospovirus-plant-vector interaction is a specific and complex relationship. It is established that several factors influence this interaction leading to high variability of transmission efficiency of the virus within a vector population. We studied the contribution of vector gender to this interaction using Frankliniella occidentalis (western flower thrips) reared on either Tomato spotted wilt virus (TSWV) infected or uninfected Capsicum annum leaflets throughout their larval stages. Later pupae were individually transferred onto healthy leaf disks to examine the differences in: survival, development rate, transmission efficiency and feeding behavior between males and females in all the treatments. This was based on the hypothesis that sex of the vector influences transmission efficiency within the vector population. Our results showed that males had significantly higher longevity, lower mortality and shorter development time compared to females, while in the comparison of feeding behaviour, females were found to feed more intensively than males, regardless of whether they were exposed or unexposed to TSWV. Conversely, transmission efficiency; which referred to successful inoculation and establishment of the virus in the host plant after a given period of inoculative feeding, was found to be significantly higher in males compared to females, despite females having the highest percentage of transmitting individuals. These findings account in part for the high variability in vector competence of F. occidentalis within a population, which further give insight into the biological factors that may influence the transmission of TSWV by F. occidentalis. [ABSTRACT FROM AUTHOR]

Reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) is a reliable technique for measuring and evaluating gene expression during variable biological processes. To facilitate gene expression studies, normalization of genes of interest relative to stable reference genes is crucial. The western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), the main vector of tomato spotted wilt virus (TSWV), is a destructive invasive species. In this study, the expression profiles of 11 candidate reference genes from nonviruliferous and viruliferous F. occidentalis were investigated. Five distinct algorithms, geNorm, NormFinder, BestKeeper, the ΔCt method, and RefFinder, were used to determine the performance of these genes. geNorm, NormFinder, BestKeeper, and RefFinder identified heat shock protein 70 (HSP70), heat shock protein 60 (HSP60), elongation factor 1 α, and ribosomal protein l32 (RPL32) as the most stable reference genes, and the ΔCt method identified HSP60, HSP70, RPL32, and heat shock protein 90 as the most stable reference genes. Additionally, two reference genes were sufficient for reliable normalization in nonviruliferous and viruliferous F. occidentalis. This work provides a foundation for investigating the molecular mechanisms of TSWV and F. occidentalis interactions. [ABSTRACT FROM AUTHOR]

Successful transmission of tomato spotted wilt virus (TSWV) by Frankliniella occidentalis requires robust infection of the salivary glands (SGs) and virus delivery to plants during salivation. Feeding behavior and transmission efficiency are sexually-dimorphic traits of this thrips vector species. Proteins secreted from male and female SG tissues, and the effect of TSWV infection on the thrips SG proteome are unknown. To begin to discern thrips factors that facilitate virus infection of SGs and transmission by F. occidentalis , we used gel- and label-free quantitative and qualitative proteomics to address two hypotheses: (i) TSWV infection modifies the composition and/or abundance of SG-expressed proteins in adults; and (ii) TSWV has a differential effect on the male and female SG proteome and secreted saliva. Our study revealed a sex-biased SG proteome for F. occidentalis, and TSWV infection modulated the SG proteome in a sex-dependent manner as evident by the number, differential abundance, identities and generalized roles of the proteins. Male SGs exhibited a larger proteomic response to the virus than female SGs. Intracellular processes modulated by TSWV in males indicated perturbation of SG cytoskeletal networks and cell-cell interactions, i.e., basement membrane (BM) and extracellular matrix (ECM) proteins, and subcellular processes consistent with a metabolic slow-down under infection. Several differentially-abundant proteins in infected male SGs play critical roles in viral life cycles of other host-virus pathosystems. In females, TSWV modulated processes consistent with tissue integrity and active translational and transcriptional regulation. A core set of proteins known for their roles in plant cell-wall degradation and protein metabolism were identified in saliva of both sexes, regardless of virus infection status. Saliva proteins secreted by TSWV-infected adults indicated energy generation, consumption and protein turnover, with an enrichment of cytoskeletal/BM/ECM proteins and tricarboxylic acid cycle proteins in male and female saliva, respectively. The nonstructural TSWV protein NSs - a multifunctional viral effector protein reported to target plant defenses against TSWV and thrips - was identified in female saliva. This study represents the first description of the SG proteome and secretome of a thysanopteran and provides many candidate proteins to further unravel the complex interplay between the virus, insect vector, and plant host. The cartoons depicting the male and female thrips bodies (Frankliniella occidentalis) and the tomato spotted wilt virus virion were adapted from Rotenberg et al. (2015). Thrips transmission of tospoviruses. Current Opinion in Virology 15:80–89 (https://doi.org/10.1016/j.coviro.2015.08.003) for use in the graphical abstract under Elsevier license terms and conditions: license no. 5380230801599. [Display omitted] • Lipoproteins were the most abundant proteins in male and female salivary glands (SGs). • Male SG proteins perturbed by TSWV infer viral infection processes. • TSWV increased abundance of integral muscle and cuticle proteins in female SGs. • SG structural proteins were overrepresented in the saliva of TSWV-infected adults. • The TSWV silencing suppressor and effector (NSs) was secreted into female saliva. [ABSTRACT FROM AUTHOR]

California is the leading producer of lettuce (Lactuca sativa) for the United States and grows 77% of the country's supply. Prior to 2006, coastal California lettuce was only periodically and incidentally infected by a single tospoviruses species: Tomato spotted wilt virus (TSWV). However, beginning in 2006 and continuing through 2012, severe outbreaks of disease caused by Impatiens necrotic spot virus (INSV) have affected the coastal lettuce crop, though TSWV was also present. In contrast, TSWV was the only tospovirus associated with disease outbreaks in Central Valley lettuce during this period. Disease surveys conducted over two seasons (2008 and 2009) in 10 commercial fields (acreage of 6 to 20 ha) indicated that INSV was the only tospovirus associated with economically damaging disease outbreaks in lettuce in the coastal region, with incidences of 0.5 to 27% (mean = 5.7%). Molecular characterization of INSV isolates associated with these disease outbreaks revealed little genetic diversity and indicated that lettuce-infecting INSV isolates were nearly identical to those previously characterized from ornamental or other hosts from different locations in the United States and the world. Monitoring of thrips revealed moderate to large populations in all surveyed lettuce fields, and the majority of thrips identified from these fields were western flower thrips, Frankliniella occidentalis. There was significant positive correlation (r² = 0.91, P = 0.003) between thrips populations and INSV incidence in the most commonly encountered type of commercial lettuce (romaine, direct seeded, conventional) included in this study. A reverse-transcription polymerase chain reaction assay developed for detection of INSV in thrips showed promise as a monitoring tool in the field. Surveys for INSV reservoir hosts in the coastal production area revealed that the weeds little mallow (Malva parvifolia) and shepherd's purse (Capsella bursa-pastoris) were commonly infected. M. parvifolia plants infected in the field did not show obvious symptoms, whereas plants of this species inoculated in the laboratory with INSV by sap transmission developed necrotic spots and chlorosis. Eleven other weed species growing in the lettuce production areas were found to be hosts of INSV. Coastal crops found to be infected with INSV included basil (Ocimum basilicum), bell pepper (Capsicum annuum), calla lily (Zantedeschia aethiopica), faba bean [Vicia faba), radicchio (Cichorium intybus), and spinach (Spinacia oleráceo). Thus, it is likely that INSV was introduced into coastal California lettuce fields via viruliferous thrips that initially acquired the virus from other local susceptible plant species. Results of this study provide a better understanding of INSV epidemiology in coastal California and may help growers devise appropriate disease management strategies. [ABSTRACT FROM AUTHOR]

Thrips-borne tospoviruses cause numerous plant diseases that produce severe economic losses worldwide. In the disease system, thrips not only damage plants through feeding but also transmit causative agents of epidemics. In addition, thrips are infected with tospoviruses in the course of virus transmission. Most studies on the effect of tospoviruses on vector thrips have focused on the Tomato spotted wilt virus–Frankliniella occidentalis system. Thus, we focused on another thrips-borne tospovirus, Watermelon silver mottle virus (WSMoV), to examine the effect of virus infection on its vector, Thrips palmi. In this study, the direct and indirect effects of WSMoV on the life history traits and feeding preference of T. palmi were examined. The survival rate and developmental time of the WSMoV-infected larval thrips did not differ significantly from those of the virus-free thrips. Comparing the developmental time of larval thrips fed on the healthy plants, thrips-damaged plants, and thrips-inoculated plants (the WSMoV-infected plants caused by thrips feeding), feeding on the thrips-damaged plants reduced the developmental time, and the WSMoV infection in host plants partially canceled the effect of thrips damage on the developmental time. In addition, no significant variations between the virus-free and WSMoV-infected adult thrips regarding longevity and fecundity were observed. These results implied that WSMoV did not directly affect the life history traits of T. palmi, but the WSMoV infection indirectly affected the development of T. palmi through the virus-infected plants. Furthermore, feeding preference tests indicated that T. palmi preferred feeding on either the thrips-damaged plants or the thrips-inoculated plants to the healthy plants. The effect of tospoviruses on the life history and feeding preference of vector thrips might vary among host plants, virus species, vector species, and environmental factors. [ABSTRACT FROM AUTHOR]

Thrips-borne tospoviruses cause numerous plant diseases that produce severe economic losses worldwide. In the disease system, thrips not only damage plants through feeding but also transmit causative agents of epidemics. In addition, thrips are infected with tospoviruses in the course of virus transmission. Most studies on the effect of tospoviruses on vector thrips have focused on the Tomato spotted wilt virus–Frankliniella occidentalis system. Thus, we focused on another thrips-borne tospovirus, Watermelon silver mottle virus (WSMoV), to examine the effect of virus infection on its vector, Thrips palmi. In this study, the direct and indirect effects of WSMoV on the life history traits and feeding preference of T. palmi were examined. The survival rate and developmental time of the WSMoV-infected larval thrips did not differ significantly from those of the virus-free thrips. Comparing the developmental time of larval thrips fed on the healthy plants, thrips-damaged plants, and thrips-inoculated plants (the WSMoV-infected plants caused by thrips feeding), feeding on the thrips-damaged plants reduced the developmental time, and the WSMoV infection in host plants partially canceled the effect of thrips damage on the developmental time. In addition, no significant variations between the virus-free and WSMoV-infected adult thrips regarding longevity and fecundity were observed. These results implied that WSMoV did not directly affect the life history traits of T. palmi, but the WSMoV infection indirectly affected the development of T. palmi through the virus-infected plants. Furthermore, feeding preference tests indicated that T. palmi preferred feeding on either the thrips-damaged plants or the thrips-inoculated plants to the healthy plants. The effect of tospoviruses on the life history and feeding preference of vector thrips might vary among host plants, virus species, vector species, and environmental factors. [ABSTRACT FROM AUTHOR]

Tomato spotted wilt virus (TSWV) is the type member of tospoviruses (genus Tospovirus), plant-infecting viruses that cause severe damage to ornamental and vegetable crops. Tospoviruses are transmitted by thrips in the circulative propagative mode. We generated a collection of NSs-defective TSWV isolates and showed that TSWV coding for truncated NSs protein could not be transmitted by Frankliniella occidentalis. Quantitative reverse transcription (RT)-PCR and immunostaining of individual insects detected the mutant virus in second-instar larvae and adult insects, demonstrating that insects could acquire and accumulate the NSs-defective virus. Nevertheless, adults carried a significantly lower viral load, resulting in the absence of transmission. Genome sequencing and analyses of reassortant isolates showed genetic evidence of the association between the loss of competence in transmission and the mutation in the NSs coding sequence. Our findings offer new insight into the TSWV-thrips interaction and Tospovirus pathogenesis and highlight, for the first time in the Bunyaviridae family, a major role for the S segment, and specifically for the NSs protein, in virulence and efficient infection in insect vector individuals. [ABSTRACT FROM AUTHOR]

Thrips-transmitted Tomato spotted wilt virus (TSWV) has a broad host range including crops and weeds. In Georgia, TSWV is known to consistently affect peanut, tomato, pepper, and tobacco production. These crops are grown from March through November. In the crop-free period, weeds are presumed to serve as a green bridge for thrips and TSWV. Previous studies have identified several winter weeds as TSWV and thrips hosts. However, their ability to influence TSWV transmission in crops is still not completely understood. To further understand these interactions, population dynamics of two prevalent vectors, viz., Frankliniella fusca (Hinds) and Frankliniella occidentalis (Pergande), on selected winter weeds were monitored from October through April in four counties from 2004 to 2008. Peak populations were typically recorded in March. E fusca and F. occidentalis adults were found on winter weeds and their percentages ranged from 0 to 68% in comparison with other adults. Immatures outnumbered all adults. Microcosm experiments indicated that the selected winter weeds differentially supported F. fusca reproduction and development. The time required to complete one generation (adult to adult) ranged from 11 to 16 d. Adult recovery ranged from 0.97 to 2.2 per female released. In addition, transmission assays revealed that thrips efficiently transmitted TSWV from peanut to weeds, the incidence of infection ranged from 10 to 55%. Back transmission assays with thrips from TSWV-infected weeds resulted in up to 75% TSWV infection in peanut. These whole-plant transmission and back transmission assays provide the basis for TSWV persistence in farmscapes year round. [ABSTRACT FROM AUTHOR]

Surveys of thrips and Tomato spotted wilt virus (TSWV) on weeds were conducted in the eastern Mediterranean region of Turkey during the years 2004-2006. Thrips species were collected by vigorously shaking weedy plants into a white container for 15 sec. Plant material collected during field surveys and plants which were used for mechanical inoculation of TSWV, were tested by DAS-ELISA. The weed species Ranunculus muricatus, Melilotus officinalis, Sinapis arvensis and Portulaca oleracea were used for the virus transmission experiments in an enclosed high plastic tunnel and in cage experiments. Western flower thrips, Frankliniella occidentlis (Pergande) (Thysanoptera: Thripidae), was the most common thrips, inhabiting 80 of the 82 weed species sampled. Adults of F. occidentalis and thrips larvae were significantly more abundant on S. arvensis than on the other weed species sampled ( P<0.05). Adult and larval thrips showed peak densities on most weeds in April or May. Summer annual weeds were not good hosts for reproduction of the thrips. A total of 90 samples from 17 plant species belonging to 11 plant families were ELISA positive for TSWV. No TSWV was detected on 65 weed species belonging to 26 plant families. High numbers of plant samples infected by TSWV were obtained in P. oleracea (21 samples) and in R. muricatus (15 samples). In field surveys symptoms of TSWV were detected on only R. muricatus. Incidence of the TSWV on weeds ranged between 5% and 25%. Transmission rates of TSWV by F. occidentalis to the weeds ranged from 33% to 83% in the pepper plastic tunnel and cage experiments. [ABSTRACT FROM AUTHOR]

In Hungary resurgence of Tomato spotted wilt virus (TSWV) frequently causes heavy crop losses in pepper production since the mid nineties. Management of TSWV control was first directed against the thrips (using different insecticides or plastic traps), and against weeds as host plants of the virus and the thrips. Later on Tsw resistance gene was introduced into different types of pepper. In 2010 and 2011 sporadically, but in 2012 more frequently a resistance breaking strain of TSWV on resistant pepper cultivars was observed in the Szentes region (Hungary). It is supposed that outbreaks of TSWV infection was due to the fact that protection against Frankliniella occidentalis was neglected and some effective pesticides (like Unifos 50 EC) were withdrawn. [ABSTRACT FROM AUTHOR]

The general principles in pathogen transmission by insects involve a complex and specific interplay, in this case between thrips, tospovirus and their shared host plant, which has led to outbreaks of crop disease epidemics of economic and social importance. The possible processes and factors driving their co-evolution were partly studied by rearing Frankliniella occidentalis [western flower thrips ( WFT)] on either tomato spotted wilt virus ( TSWV)-infected or uninfected Capsicum annum leaflets throughout their larval stages. Later, pupae were transferred individually on healthy leaf discs for further studies of the influence of TSWV on WFT development and behavioural patterns. The exposure of WFT to TSWV was found to improve performance with regard to longevity and survival, with mean longevity being significantly higher in TSWV-exposed WFT compared to unexposed ones (F(3,403) = 22.44, P < 0.0001). The observed improvement in survival was as a result of significant reduction in mortality for the WFT individuals exposed to TSWV (F(3,383) = 849.94, P < 0.0001) compared to the unexposed. However, the results showed a significant reduction in mean daily fecundity overtime (F10,10) = 246.66, P < 0.0001) and across the four treatments (F(3,30) = 6.62, P = 0.001), as well as lifetime fecundity (F(3,23) = 21.23, P < 0.0001) of the WFT exposed to TSWV compared to the unexposed reared on uninfected leaf discs. For preferential test, C. annum leaf discs infected with TSWV were more attractive to WFT as compared to healthy leaf discs (χ2(4, 34) = 112.35, P < 0.0001). These results are envisaged to contribute to a clear understanding into the plant-vector-virus interaction, which is essential for accurate diagnosis and control of the TSWV epidemic, as well as the control of F. occidentalis as crop pest. [ABSTRACT FROM AUTHOR]

Abstract: The western flower thrips (WFT), Frankliniella occidentalis, a world-wide invasive insect, causes agricultural damage by directly feeding and by indirectly vectoring Tospoviruses, such as Tomato spotted wilt virus (TSWV). We characterized the transcriptome of WFT and analyzed global gene expression of WFT response to TSWV infection using Illumina sequencing platform. We compiled 59,932 unigenes, and identified 36,339 unigenes by similarity analysis against public databases, most of which were annotated using gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Within these annotated transcripts, we collected 278 sequences related to insecticide resistance. GO and KEGG analysis of different expression genes between TSWV-infected and non-infected WFT population revealed that TSWV can regulate cellular process and immune response, which might lead to low virus titers in thrips cells and no detrimental effects on F. occidentalis. This data-set not only enriches genomic resource for WFT, but also benefits research into its molecular genetics and functional genomics. [Copyright &y& Elsevier]