Influence of tomato spotted wilt virus on performance and behaviour of western flower thrips (Frankliniella occidentalis)

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 (F_10,10) = 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.     

Direct and indirect effects of a thrips‐transmitted Tospovirus on the preference and fitness of its vector,Frankliniella fusca

Phytoviruses including tospoviruses are known to affect the behavior and fitness of their vectors both positively and negatively. In this study, we investigated the effects of Tomato spotted wilt virus (TSWV) (family Bunyaviridae, genus Tospovirus) infection on the fitness and feeding ability of tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) using peanut, Arachis hypogaea L. (Fabaceae), as a host. Potentially viruliferous F. fusca laid more eggs than non‐viruliferous F. fusca. In contrast, fewer potentially viruliferous F. fusca developed into adults and required a longer developmental time than non‐viruliferous F. fusca, indicating a direct negative effect of the virus on thrips fitness. In addition, no‐choice feeding tests indicated that non‐viruliferous F. fusca fed more rapidly than potentially viruliferous F. fusca. Typically, phytovirus infections are known to enhance the availability of vital nutrients such as free amino acids in infected host plants and to affect other important physiological processes negatively. Free amino acids are known to play a vital role in egg production and development. Further investigations in this study revealed that leaflets of infected plants had ca. 15 times more free amino acids than non‐infected leaflets. TSWV‐infected leaflets were used to rear potentially viruliferous thrips. Higher amino acid levels in TSWV‐infected leaflets than in non‐infected leaflets could have contributed to increased oviposition by potentially viruliferous F. fusca compared to non‐viruliferous F. fusca. Taken together, these results suggest that increased concentrations of free amino acids in TSWV‐infected plants might serve as an incentive for thrips feeding on otherwise unsuitable hosts, thereby facilitating TSWV acquisition and transmission.     

Obstructor,a Frankliniella occidentalis protein,promotes transmission of tomato spotted wilt orthotospovirus

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 G_N (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 G_N 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.     

Propagation of tomato spotted wilt virus in Frankliniella occidentalis does neither result in pathological effects nor in transovarial passage of the virus

The effect of tomato spotted wilt virus (TSWV) on Frankliniella occidentalis Pergande (Thysanoptera; Thripidae) following a 6-hour acquisition access period on infected plants was investigated. No statistically significant differences were observed among viruliferous, non-viruliferous and control thrips with respect to developmental time, reproduction rate and survival. Thrips larvae, exposed or non-exposed to TSWV, developed from egg to adult in 13.1 and 13.2 days, respectively. Exposed females produced an average of 28.3 larvae whereas control thrips produced 22.3 larvae and longevity was 13.4 and 12.5 days, respectively. None of these values were significantly different. Population reproductive statistics, net reproductive rate (R ₀), mean generation time (T) and intrinsic rate of increase (r _m) were calculated from the life fertility tables. R ₀ and r _m were higher for viruliferous thrips as compared to non-viruliferous and non-exposed thrips. Virus transmission studies revealed that viruliferous thrips were able to transmit virus until death and that TSWV was not transovarially transmitted.     

Occurrence and localization of spherical viruslike particles in tissues of apparently healthy tobacco thrips,Frankliniella fusca,a vector of tomato spotted wilt virus

Spherical viruslike particles (VLP) were found in the tissues of apparently healthy tobacco thrips, Frankliniella fusca. The particles occurred in abundance in thrips from Ontario but were absent in thrips from Oklahoma reared under identical conditions. The VLP were not transmissible to any of the seven plant hosts (in four families) of F. fusca suggesting that they may be an insect virus. Transmission of tomato spotted wilt virus (TSWV) by F. fusca, a known vector, was not affected by the presence or absence of the VLP. No TSWV particles were detected in tissues of F. fusca that transmitted TSWV to test plants. The VLP occurred in several internal organs and hemocoele of the thrips and were isolated in vitro by preparing homogenates of gut tissues. Infection of oocytes and presence of VLP in young nymphs suggested transovarial transmission of the particles. The VLP measured 62 ± 4 nm in diameter and usually occurred in dense viroplasms in the cell cytoplasm. Development of the particles within the viroplasms is discussed.     

云南省昆明地区番茄斑萎病毒核衣壳蛋白和运动蛋白变异分析

为了明确对番茄斑萎病毒(tomato spotted wilt virus,TSWV)免疫的番茄YNAU335自交系表现出TSWV感病症状(抗性被打破)的原因,在排除YNAU335自交系不纯和或混杂其它感病番茄材料的因素外,选取96172I(感病)和YNAU335(抗性被打破)自交系感病植株,进行TSWV核衣壳蛋白(nucleocapsid protein,NP)和运动蛋白(movement protein,MP)基因的RT-PCR检测,并对阳性克隆进行基因测序分析。结果表明:(1)2个自交系中均克隆出TSWV的NP和MP基因,共获得5条NP(登录号:MK628735～MK628739)和3条MP(登录号:MK883723、MK883724和MK887284)多态性基因序列。(2)96172I感病材料中克隆出以上所有基因序列,YNAU335感病材料中克隆出其中的3条NP和1条MP基因序列。(3)对YNAU335中TSWV特有的NP和MP氨基酸突变位点进行分析,结果发现4个特异突变位点可能与打破YNAU335抗性有关,4个突变位点分别为:NP 18位氨基酸G突变为V,36位T突变为I,39位L突变为R,MP 274位E突变为K。(4)系统发育分析显示,5条NP和3条MP与云南省已登记的NP和MP聚类在不同的分支,表明云南省昆明地区TSWV存在丰富的遗传多样性。     

Role of insecticides in reducing thrips injury to plants and incidence of tomato spotted wilt virus in Virginia market-type peanut

Tomato spotted wilt virus (family Bunyaviridae, genus Tospovirus, TSWV), transmitted by many thrips species, is a devastating pathogen of peanut, Arachis hypogaea L. TSWV has become a serious problem in the Virginia/Carolina peanut-growing region of the United States. During 2002, TSWV was present in 47% of the North Carolina hectarage and caused a 5% yield reduction in Virginia. Factors influencing levels of TSWV in runner market-type peanut cultivars, which are primarily grown in Alabama, Flordia, Georgia, and Texas, have been integrated into an advisory to help those peanut growers reduce losses. An advisory based on the southeast runner market-type version is currently under development for virginia market-type peanut cultivars that are grown primarily in the Virginia/ Carolina region. A version based on preliminary field experiments was released in 2003. One factor used in both advisories relates to insecticide use to reduce the vector populations and disease incidence. This research elucidated the influence of insecticides on thrips populations, thrips plant injury, incidence of TSWV, and pod yield in virginia market-type peanut. Eight field trials from 2003 to 2005 were conducted at two locations. In-furrow application of aldicarb and phorate resulted in significant levels of thrips control, significant reductions in thrips injury to seedlings, reduced incidence of TSWV, and significant increases in pod yield. Foliar application of acephate after aldicarb or phorate applied in the seed furrow further reduced thrips plant injury and incidence of TSWV and improved yield. These findings will be used to improve the current virginia market-type TSWV advisory.     

Temporal and spatial dynamics of Tomato spotted wilt virus and its vector in a potato crop in Argentina

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.     

Влнянне характера эаселення ноля капустноii совкоii(Barathra brassicae L.) эффективноеть трихограммы (Trichogramma evanescens Westw.) (Lepidoptera,Noctuidae; Hymenoptera,Trichogrammatidae)

TSWV belongs to the genus Tospovirus which was established in the family Bunyaviridae, a family of animal viruses. Besides TSWV, Impatiens necrotic spot virus (INSV) and ground nut bud necrosis virus (GBNV) were established as different Tospovirus species. Tospoviruses have quasispherical particles of 85 nm diametre which are surrounded by a membrane and contain 3 RNA species and 4 structural proteins. In Tospovirus infected plant cells virions were detected in cavaties of the endoplasmatic reticulum and additionally amorphous electron dense material accumulates in infected cells. Defective forms of TSWV lack the ability to form complete virus particles. TSWV is the only plant pathogenic virus that is transmitted by thrips which transmit the virus with different efficiency. The virus has an extensive plant host range of more than 360 different species. The developing symptoms depend on the Tospovirus species, the virulence of the virus strains and the environmental conditions.

Based on the reaction of TSWV isolates with N‐specific polyclonal antisera, 3 serogroups were established. The most frequently used technique for serologically based diagnosis of Tospoviruses is DAS ELISA with N‐specific or preadsorbed antisera against complete virus. For TSWV epidemiology distinct weeds and cultural host plants play an important role for the survival of virus and vector. Breeding for resistance is the most important preventive measure of control.     

Preference of the vector thrips Frankliniella occidentalis for plants infected with thrips‐non‐transmissible Tomato spotted wilt virus

The effect of a thrips‐non‐transmissible Tomato spotted wilt virus (TSWV) on insect–host interactions between thrips and Arabidopsis thaliana was analysed. A wild‐type TSWV virulent isolate and a TSWV isolate that induces mild symptoms on inoculated plants (TSWV‐Mo) were used in this study, and TSWV‐Mo isolate was obtained by single local lesion isolation using Petunia x hybrid after several passages on Nicotiana rustica plants. In transmission test, although wild‐type TSWV (TSWV‐wt) was transmitted by two thrips species (transmission ratio; Frankliniella occidentalis, 25%; Thrips tabaci, 10%; and T. palmi, 0%), none of the thrips transmitted TSWV‐Mo. Feeding damage by F. occidentalis in A. thaliana plants was more extensive on TSWV‐wt‐infected plants than on TSWV‐Mo‐infected plants, despite comparable preference. Among the markers of plant defences, salicylic acid‐regulated genes were upregulated threefold to sixfold by TSWV‐wt or TSWV‐Mo infection. In contrast, jasmonate‐regulated genes and jasmonate/ethylene‐regulated genes were not affected by the infections. Pull assays showed that adjacent TSWV‐Mo‐infected plants were preferred over uninfected plants. In conclusion, our results showed that the transmissibility by thrips of TSWV is not related to preference of vector thrips and suggested that TSWV‐Mo‐infected plants may be used as attractants for behaviour control of thrips.     

番茄斑萎病毒对多杀菌素抗性西花蓟马发育繁殖和药剂敏感性的影响

【目的】西花蓟马Frankliniella occidentalis (Pergande)是重要的入侵害虫,是番茄斑萎病毒（TSWV）最有效的传播媒介,TSWV对西花蓟马的生长发育有一定的影响。多杀菌素是防治西花蓟马最有效的药剂之一,但已有田间西花蓟马对多杀菌素产生抗药性的报道。TSWV对抗性西花蓟马是否也有影响及程度如何尚不清楚。本研究通过对此问题进行深入研究,以期为进一步了解TSWV对西花蓟马的影响提供依据。【方法】应用特定年龄-龄期及两性生命表的方法,研究用番茄斑萎病毒处理和未处理的多杀菌素抗性和敏感西花蓟马种群的生物学特性;用叶管药膜法测定不同处理种群对3种药剂（多杀菌素、甲氨基阿维菌素苯甲酸盐和虫螨腈）的敏感性变化。【结果】对于抗性品系,TSWV处理后西花蓟马的发育历期缩短,雌成虫寿命和产卵量略高,但与对照组差异不显著(P＞0.05),内禀增长率（r）和净生殖率（R₀）分别为0.0433 d^-1和2.210,显著高于对照组（分别为0.0356 d^-1和1.972）（P ≤ 0.001）。对于敏感品系,TSWV处理后西花蓟马的发育历期缩短,雌雄成虫寿命均显著延长（P ≤ 0.001）,产卵量也略有提高,R₀为4.125,显著高于对照组（3.979）（P ≤ 0.001）。TSWV处理后敏感和抗性西花蓟马对多杀菌素的敏感性没有发生明显变化,对甲氨基阿维菌素苯甲酸盐和虫螨腈的敏感性显著降低。【结论】番茄斑萎病毒对多杀菌素敏感和抗性西花蓟马均有直接有利影响,病毒处理的西花蓟马发育历期缩短,繁殖能力增强,成虫寿命延长,对药剂的敏感性降低。     

Does natural deposition of pine pollen affect the ovipositional behavior of Frankliniella occidentalis and Frankliniella fusca?

Tree pollen, especially Pinus spp. (Pinaceae), is shed in large quantities every spring in North America. Pine pollen deposition onto leaves was found to significantly influence the ovipositional behaviors of certain thrips species (Thysanoptera: Thripidae) in peanut and tomato leaf choice and no‐choice tests. Pine pollen (Pinus elliottii Engelm.) increased the oviposition rate 2.9‐fold for Frankliniella occidentalis (Pergande) (western flower thrips) and 1.6‐fold for Frankliniella fusca (Hinds) (tobacco thrips) in choice tests averaged over both plant species. These results support the idea that pollen has a greater impact on F. occidentalis behavior than on F. fusca behavior. The most dramatic increase was in peanut, where F. occidentalis only oviposited on leaves dusted with pollen, suggesting that the addition of pollen stimulated this flower thrips to lay eggs on a poor host‐plant part. The impact of pollen on the rate of oviposition by thrips is important because it is the early‐instar nymphs that acquire tomato spotted wilt virus (TSWV), which these two thrips species vector. In a laboratory bioassay, the addition of pine pollen to TSWV‐infected peanut foliage increased the percentage of infected F. fusca after one generation.     

Variation in thrips species composition in field crops and implications for tomato spotted wilt epidemiology in North Carolina

Thrips were surveyed in tomato spotted wilt-susceptible crops in five areas across North Carolina. Tomato, pepper, and tobacco plants in commercial fields were sampled and 30 species of thrips were collected over a 3-year period. The most common species overall was Frankliniella tritici (Fitch). The most common thrips species that are known to vector Tomato Spotted Wilt Virus (TSWV) were F. fusca (Hinds), and F. occidentalis (Pergande). Relatively low numbers of Thrips tabaci Lindeman, another reported vector, were collected. The spatial and temporal occurrence of vectors varied with sampling method, crop species, region of North Carolina, and localized areas within each region. In a laboratory experiment, no difference was detected between the ability of F. fusca and F. occidentalis to acquire and transmit a local isolate of TSWV. Based on vector efficiency and occurrence, F. fusca is considered the most important vector of TSWV in tobacco, whereas both F. fusca and F. occidentalis are important vectors of TSWV in tomato and pepper.     

Determination of key residues in tospoviral NSm required for Sw-5b recognition,their potential ability to overcome resistance,and the effective resistance provided by improved Sw-5b mutants

Sw-5b is an effective resistance gene used widely in tomato to control tomato spotted wilt virus (TSWV), which causes severe losses in crops worldwide. Sw-5b confers resistance by recognizing a 21-amino-acid peptide region of the viral movement protein NSm (NSm21, amino acids 115–135). However, C118Y or T120N mutation within this peptide region of NSm has given rise to field resistance-breaking (RB) TSWV isolates. To investigate the potential ability of TSWV to break Sw-5b-mediated resistance, we mutagenized each amino acid on NSm21 and determined which amino acid mutations would evade Sw-5b recognition. Among all alanine-scan mutants, NSm^P119A, NSm^W121A, NSm^D122A, NSm^R124A, and NSm^Q126A failed to induce a hypersensitive response (HR) when coexpressed with Sw-5b in Nicotiana benthamiana leaves. TSWV with the NSm^P119A, NSm^W121A, or NSm^Q126A mutation was defective in viral cell-to-cell movement and systemic infection, while TSWV carrying the NSm^D122A or NSm^R124A mutation was not only able to infect wild-type N. benthamiana plants systemically but also able to break Sw-5b-mediated resistance and establish systemic infection on Sw-5b-transgenic N. benthamiana plants. Two improved mutants, Sw-5b^{L33P/K319E/R927A} and Sw-5b^{L33P/K319E/R927Q}, which we recently engineered and which provide effective resistance against field RB isolates carrying NSm^C118Y or NSm^T120N mutations, recognized all NSm21 alanine-substitution mutants and conferred effective resistance against new experimental RB TSWV with the NSm^D122A or NSm^R124A mutation. Collectively, we determined the key residues of NSm for Sw-5b recognition, investigated their potential RB ability, and demonstrated that the improved Sw-5b mutants could provide effective resistance to both field and potential RB TSWV isolates.     

Variety,mulch and stage of inoculation effects on incidence of tomato spotted wilt virus disease in cucumber (Cucumis sativus L.)

Abstract

Tomato spotted wilt virus (TSWV) vectored by thrips is one of the major diseases affecting cucumber yield. Control of thrips is an underlying factor in its management. A study was conducted to determine the effect of time of inoculation, variety and mulch on disease incidence. Four varieties were inoculated with TSWV at cotyledon, 3 – 4 leaf and flower bud stages in a RCBD experiment replicated four times in a greenhouse. In the field, a 2×8 factorial design where two cucumber varieties were raised on seven types of mulches (red, yellow, silver, clear, black, white, and straw) with unmulched plots as controls was used. Variety Marketer was more tolerant to the disease compared to other varieties. Most varieties were generally tolerant to TSWV at cotyledonous but susceptible at 3 – 4 leaf and flower bud stages. Silver and clear mulches significantly suppressed thrip populations, yield and quality under field conditions.     

Multi‐targeting of viral RNAs with synthetic trans‐acting small interfering RNAs enhances plant antiviral resistance

RNA interference (RNAi)‐based tools are used in multiple organisms to induce antiviral resistance through the sequence‐specific degradation of target RNAs by complementary small RNAs. In plants, highly specific antiviral RNAi‐based tools include artificial microRNAs (amiRNAs) and synthetic trans‐acting small interfering RNAs (syn‐tasiRNAs). syn‐tasiRNAs have emerged as a promising antiviral tool allowing for the multi‐targeting of viral RNAs through the simultaneous expression of several syn‐tasiRNAs from a single precursor. Here, we compared in tomato plants the effects of an amiRNA construct expressing a single amiRNA and a syn‐tasiRNA construct expressing four different syn‐tasiRNAs against Tomato spotted wilt virus (TSWV), an economically important pathogen affecting tomato crops worldwide. Most of the syn‐tasiRNA lines were resistant to TSWV, whereas the majority of the amiRNA lines were susceptible and accumulated viral progenies with mutations in the amiRNA target site. Only the two amiRNA lines with higher amiRNA accumulation were resistant, whereas resistance in syn‐tasiRNA lines was not exclusive of lines with high syn‐tasiRNA accumulation. Collectively, these results suggest that syn‐tasiRNAs induce enhanced antiviral resistance because of the combined silencing effect of each individual syn‐tasiRNA, which minimizes the possibility that the virus simultaneously mutates all different target sites to fully escape each syn‐tasiRNA.     

Effects of tomato spotted wilt virus (TSWV) isolates, host plants, and temperature on survival, size, and development time of Frankliniella fusca

The effects of different isolates of the tomato spotted wilt tospovirus (TSWV), host plants, and temperatures on Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), the most important vector of TSWV in North Carolina, were measured in the laboratory. Thrips were reared at either 18.3, 23.9, or 29.4 °C until adult eclosion on excised leaves of Datura stramonium L. or Emilia sonchifolia (L.). Plants were either infected with the TSWV isolates CFL or RG2, or left uninfected (control). The results revealed a positive relationship between larval survival and temperature, regardless of host plant or TSWV isolate. Both survival to adult and percentage transmission of TSWV by F. fusca were significantly affected by the interaction between host plant and TSWV isolate. The consequence of this interaction was that the cohort‐based percentage transmission from infected E. sonchifolia plants for CFL was 1.3‐fold greater than that of RG2, whereas the percentage transmission from infected D. stramonium plants for RG2 was twice that of CFL. Both host plant and TSWV isolates showed significant effects on thrips development time to adult and head capsule width of adult thrips, as well as on the incidence of thrips infection with TSWV. The infection status of these thrips was determined by ELISA for the NSs viral protein. Infected thrips reared on infected host foliage took longer to develop to adult and were smaller than non‐infected thrips which had also been reared on infected host foliage, demonstrating a direct effect of the TSWV on thrips. However, non‐infected thrips reared on non‐infected leaves took longer to develop than non‐infected thrips reared on infected leaves, suggesting an effect of the plant tissue on thrips. In addition, adult thrips reared on TSWV‐infected D. stramonium at 29.4 °C developed smaller head capsules than thrips developing on infected foliage at lower temperatures and on non‐infected leaves of D. stramonium or E. sonchifolia. Both TSWV isolates and host plants differentially affected females more than males. In conclusion, both the infection of thrips by TSWV and TSWV‐mediated changes in host plant quality were found to have significant biological effects on F. fusca.     

Potential of bioinsecticidal Bacillus thuringiensis inoculum to suppress gray mold in tomato based on induced systemic resistance

The potential of the active ingredient of a commercial bioinsecticide, XenTari^® (Bacillus thuringiensis [BT] serovar aizawai strain ABTS‐1857), to suppress gray mold in tomato plants was elucidated. First, a suspension of the active ingredient of XenTari^® and a liquid culture of the bacterial strain as BT inocula were sprayed onto detached leaves or drenched into pots of tomato seedlings, and then, propagules of the gray mold fungus, Botrytis cinerea, were inoculated onto the leaves. The gray mold disease was significantly suppressed when rhizospheres were drenched with either inoculum, but not when inocula were sprayed onto detached leaves of seedlings. Both BT inocula were verified not to directly inhibit the mycelial growth of B. cinerea based on in vitro culture plate assays. Additionally, real‐time RT‐PCR analysis verified that the active ingredient increased the expression levels of defence‐related genes, such as PR‐1(P6) and P4, in the leaves of tomato seedlings. These results suggest that the active ingredient has the potential to suppress gray mold disease in tomato, not through direct antagonistic interactions with B. cinerea, but rather through systemic activation of the plant defence system by increased expression of several defence‐related genes.     

The impact of a parasitic nematode, Thripinema fuscum, on the feeding behavior and vector competence of Frankliniella fusca

Frankliniella fusca (Hinds) (Thysanoptera: Thripidae) is the predominant thrips species found inhabiting and reproducing in peanut, Arachis hypogaea L. (Fabaceae), and is one of at least seven thrips species reported to transmit Tomato spotted wilt virus (TSWV). The entomogenous nematode Thripinema fuscum Tipping & Nguyen (Tylenchida: Allantonematidae), a natural enemy of F. fusca , parasitizes larval and adult populations under field conditions. All known Thripinema species render the host female thrips sterile and have the potential to suppress pest populations to near extinction. As a result, secondary spread of TSWV in peanut is reduced. Reduction of the virus under field conditions may also be due to lower transmission rates caused by parasite-induced alterations in host feeding behavior. Therefore, the feeding rates of healthy and parasitized F. fusca male and female cohorts on leaf discs were recorded daily for 10 days and digital images were subjected to image analysis and viral transmission rates were compared daily using double antibody sandwich enzyme-linked immunosorbent assay. Thripinema fuscum reduced the feeding of female F. fusca by nearly 65%, and the ability of females to transmit TSWV by 50%. Potential mechanisms underlying the parasite-induced alterations in feeding behavior and transmission are discussed. Parasitism by T. fuscum significantly reduced male longevity, but female longevity was not affected. These results provide further evidence that T. fuscum aids in regulating viruliferous F. fusca pest populations and suggests its potential as a biological control agent for inoculative release in peanut.