Protection of livestock against bluetongue virus vector Culicoides imicola using insecticide‐treated netting in open areas

The protection of livestock against Culicoides species (Diptera: Ceratopogonidae) using physical barriers or chemically treated barriers is difficult owing to the small size of these biting midges and animal welfare concerns associated with the reduction of air flow. Culicoides imicola Kieffer is the main bluetongue virus vector in the Mediterranean basin, including the southern Iberian peninsula, where livestock is mainly housed in open pens or sheds which offer no physical protection against C. imicola. In this study we assessed the efficacy of surrounding yearling ewe pens with a canvas barrier or a cypermethrin‐treated canvas barrier in reducing the entry of Culicoides spp. and C. imicola. Analyses were based on comparisons of Culicoides catches in traps in pens with and without barriers, and in traps located outside pens. Although there was no clear reduction in the abundance of Culicoides other than C. imicola in pens with either barrier, the C. imicola presence was markedly reduced by the insecticide‐treated barrier compared with the untreated barrier; the latter did not reduce the abundance of this species in pens. Estimates of the protection conferred against C. imicola by the treated barrier differed depending on whether catch comparisons were based on outside traps or on traps located inside no‐barrier pens. The results suggest that the use of insecticide‐treated barriers may reduce contact between livestock and C. imicola in open areas or sheds. More research is necessary to assess the degree of protection as a function of barrier height, C. imicola abundance, and the size of the area to be protected.     

下调烟粉虱MED隐种BtabCSP6表达对番茄黄化曲叶病毒传播的影响

【目的】番茄黄化曲叶病毒(tomato yellow leaf curl virus, TYLCV)是对农业生产造成威胁的主要病毒之一,自然条件下通过媒介昆虫烟粉虱Bemisia tabaci传播。已有研究表明烟粉虱雌成虫比雄成虫具有更强的获毒与传毒能力。本研究旨在探明烟粉虱化学感受蛋白(chemosensory protein, CSP)基因BtabCSP6表达对病毒传播的影响,为控制病毒发生寻找新途径。【方法】使用TYLCV侵染性克隆方法获得带毒番茄植株,微虫笼收集不带毒烟粉虱MED隐种成虫固定在感染TYLCV的番茄植株叶片获毒48 h;利用RT-qPCR技术测定分别取食感染和未感染TYLCV番茄植株的烟粉虱MED隐种雌雄成虫体内BtabCSP1-8基因表达量变化;通过饲喂法利用RNAi对烟粉虱MED隐种雌成虫BtabCSP6基因进行干扰48 h后饲喂TYLCV感染的番茄植株,测定烟粉虱MED隐种雌成虫的获毒率和传毒率。【结果】RT-qPCR检测结果表明,与未侵染的烟粉虱MED隐种雌成虫相比,侵染TYLCV的雌成虫体内BtabCSP3和BtabCSP6基因的表达量变化最为显著。同样...     

烟粉虱传播双生病毒研究进展

综述了烟粉虱Bemisia tabaci对双生病毒的获取、传播及存留等方面的特性。烟粉虱最短的获毒和接种时间为15～30 min;双生病毒在烟粉虱体内可存留1至数周,有的终身存在。烟粉虱对双生病毒的传毒效率除了随其获毒及传毒时间的延长、传毒烟粉虱个体数量的增加以及病毒体浓度的增加而提高外,还与烟粉虱的龄期及性别有关。双生病毒除了在植物与粉虱之间直接传播外,还可通过烟粉虱交配及经卵携带的途径在烟粉虱个体和代别间进行传播。寄主植物、双生病毒的一些特殊蛋白以及烟粉虱内共生菌产生的GroEL蛋白,都可影响烟粉虱携带的双生病毒种类及传毒的可能性。双生病毒可对烟粉虱的发育、存活和生殖产生不利或有利的影响。雌成虫携带番茄黄化曲叶病毒（tomato yellow leaf curl virus, TYLCV）后,存活力和生殖力均下降; 而携带番茄斑驳病毒（tomato mottle virus, ToMoV）后,生殖力提高。此外,植物感染双生病毒后,其对烟粉虱的适合性可能提高。     

Evaluation of barrier plants for the cultural control of tomato yellow leaf curl disease

Barrier cropping plays an essential role in controlling insect pests and insect-transmitted diseases in cultural control. It has been proven efficient in suppressing the spread of nonpersistently transmitted viruses. For suppressing the spread of persistently transmitted viruses, barrier cropping is not considered an effective control strategy because barrier plants cannot act as a virus sink to purge the virus in the vector. However, few successful cases of barrier cropping suppressing the spread of persistently transmitted viruses have been reported. The objectives of the present study were to screen candidates (cucumber, okra, Chinese kale, soybean, and corn) for potential barrier plants to control tomato yellow leaf curl Thailand virus (TYLCTHV) and examine whether prefeeding on these plants can reduce the virus titer in its vector, Bemisia tabaci, thus reducing TYLCTHV transmission. The results revealed that nonviruliferous whiteflies preferred cucumber and okra to tomato, whereas viruliferous whiteflies preferred cucumber to tomato. Although prefeeding on cucumber, okra, and Chinese kale did not reduce the titer of TYLCTHV in viruliferous whiteflies, the vector transmission rate decreased after the whiteflies fed on Chinese kale. It implies that planting Chinese kale as a barrier plant for tomato cultivation may reduce the incidence of TYLCTHV. In addition, the preference to cucumber plants may reduce the incidence of whiteflies acquiring TYLCTHV from virus-infected tomato plants and of viruliferous whiteflies inoculating the virus into healthy tomato plants, thereby reducing the disease incidence. Further field trials of barrier cropping using the candidate plants are warranted.     

The circulative pathway of begomoviruses in the whitefly vector Bemisia tabaci— insights from studies with Tomato yellow leaf curl virus

Our current knowledge concerning the transmission of begomoviruses by the whitefly vector Bemisia tabaci is based mainly on research performed on the Tomato yellow leaf curl virus (TYLCV) complex and on a number of viruses originating from the Old World, such as Tomato leaf curl virus, and from the New World, including Abutilon mosaic virus, Tomato mottle virus, and Squash leaf curl virus. In this review we discuss the characteristics of acquisition, transmission and retention of begomoviruses by the whitefly vector, concentrating on the TYLCV complex, based on both published and recent unpublished data. We describe the cells and organs encountered by begomoviruses in B. tabaci. We show immunolocalisation of TYLCV to the B. tabaci stylet food canal and to the proximal part of the descending midgut, and TYLCV‐specific labelling was also associated with food in the lumen. The microvilli and electron‐dense material in the epithelial cells of the gut wall were also labelled by the anti TYLCV serum, pointing to a possible virus translocation route through the gut wall and to a putative site of long‐term virus storage. We describe the path of begomoviruses in their vector B. tabaci and in the non‐vector whitefly Trialeurodes vaporariorum, and we follow the rate of virus translocation in these insects. We discuss TYLCV transmission between B. tabaci during mating, probably by exchange of haemolymph. We show that following a short acquisition access to infected tomato plants, TYLCV remains associated with the B. tabaci vector for weeks, while the virus is undetectable after a few hours in the non‐vector T. vaporariorum. The implications of the long‐term association of TYLCV with B. tabaci in the light of interactions of the begomovirus with insect receptors are discussed.     

Settling preferences of the whitefly vector Bemisia tabaci on infected plants varies with virus family and transmission mode

Virus infection may change not only the host‐plant phenotypic (morphological and physiological) characteristics, but can also modify the behavior of their insect vector in a mutualistic or rather antagonistic manner, to promote their spread to new hosts. Viruses differ in their modes of transmission and depend on vector behavior for successful spread. Here, we investigated the effects of the semi‐persistently transmitted Tomato chlorosis virus (ToCV, Crinivirus) and the persistent circulative Tomato severe rugose virus (ToSRV, Begomovirus) on alighting preferences and arrestment behavior of their whitefly vector Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Middle East Asia Minor 1 (MEAM1) on tomato plants (Solanum lycopersicum L. cv. Santa Clara, Solanaceae). The vector alighting preferences between infected and uninfected plants in choice assays were apparently influenced by the presence of ToCV and ToSRV in the whiteflies or by their previous exposure to infected plants. The observed changes in vector behavior do not seem to benefit the spread of ToCV: non‐viruliferous insects clearly preferred mock‐inoculated plants, whereas ToCV‐viruliferous insects landed on mock‐inoculated and ToCV‐infected plants, indicating a partial change in insect behavior – ToCV was able to directly affect the preference of its vector B. tabaci, but this change in insect behavior did not affect the virus spread because viruliferous insects landed on mock‐inoculated and infected plants indistinctly. In contrast, ToSRV‐viruliferous insects preferred to land on mock‐inoculated plants, a behavior that increases the probability of spread to new host plants. In the arresting behavior assay, the majority of the insects remained on mock‐inoculated plants when released on them. A greater number of insects moved toward mock‐inoculated plants when initially released on ToCV‐ or ToSRV‐infected plants, suggesting that these viruses may repel or reduce the nutritional quality of the host plants for B. tabaci MEAM1.     

The contribution of tomato and alternative host plants to tomato leaf curl virus inoculum pressure in different areas of South India

Indian tomato leaf curl virus (ToLCV) (Geminiviridae: Sub-group III) was detected both in field-collected and laboratory-reared B. tabaci using a triple-antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA). ToLCV was detected in six of the 10 group samples of field collected B. tabaci. ToLCV was also identified in 13 weed species commonly found in Karnataka, both by symptom expression and TAS-ELISA. ToLCV from c. 61% of infected plants was transmitted successfully to tomato by B. tabaci. Tomato plots were planted at three locations on the University of Agricultural Sciences Campus, Bangalore. Indian tomato leaf curl virus disease (ToLCVD) incidence increased most rapidly when the tomato plot was situated adjacent to an older ToLCVD-infected tomato field. When the plots were positioned in a dryland or a wetland area, at least 500 m away from any infected tomato fields, the ToLCVD incidence increased less rapidly, although in all sites it was 100% by 11 wk after transplanting. The numbers of B. tabaci caught on yellow traps in all sites increased during weeks 1–3 after transplanting and thereafter remained at between 10–15 adults trap^-1 24 h^_1. Adult numbers recorded on tomato plants by direct counts remained approximately constant at 2–4 adults plant“”¹. Tomato fields were planted in three taluks (administrative areas) of Karnataka, that had different current and previous histories of tomato production. ToLCVD incidence increased most and least rapidly, respectively, in Kolar taluk where tomato is grown continuously and Doddaballapur tuluk where tomato was grown in the area for the first time. In Malur tuluk, where tomato was grown discontinuously (once a year), the incidence of ToLCVD increased at an intermediate rate. Weed host-plant species growing near the experimental sites had averages of between 1.5–10.0 B. tabaci nymphs per plant, whereas the tomato plants had only 0.3 nymphs per plant. The percentage parasitism of B. tabaci nymphs on tomato and weed species, respectively, was 0.7% and 2–6%. Nymphs and pupae were parasitised by an Encarsia sp. and Eretmocerus mundus Mercet. The relevance and implications of these findings for the epidemiology and management of ToLCVD in Karnataka State, South India is discussed.     

Portable trench barrier for protecting edges of tomato fields from Colorado potato beetle (Coleoptera: Chrysomelidae)

Experiments were conducted to test a portable trench barrier composed of an extruded, UV-retarded, PVC plastic trough, designed to allow Colorado potato beetles, Leptinotarsa decemlineata (Say), to enter and become trapped and killed inside. Tests demonstrated that the portable plastic trenches were effective as barriers to Colorado potato beetles as they walked into tomato, Lycopersicon esculentum Mill., fields from overwintering sites in the spring. In field tests, plots that were protected by portable trench barriers had significantly fewer beetles per tomato plant, and lower levels of defoliation. Tomato yields in plots that were protected by portable trench barriers were similar to yields in plots that were protected by insecticide sprays, and significantly higher than plots where beetles were not controlled.     

The effects of sowing date and choice of insecticide on cereal aphids and barley yellow dwarf virus epidemiology in northern England

During the mid-1980s, Sitobion avenae became recognised as an important vector of barley yellow dwarf virus (BYDV) in the Vale of York. A field trial at the University of Leeds Farm, North Yorkshire, was carried out during the autumn/winter of 1984-85 to evaluate different control procedures against S. avenae-transmitted BYDV and to investigate its epidemiology. Winter barley was sown on three dates in September, and plots were sprayed with either deltamethrin, demeton-S-methyl or pirimicarb on one of three dates between mid-October and mid-November, making a factorial design. Rhopalosiphum padi, the main vector of BYDV in southern England, were rarely found during the experiment, but the numbers of S. avenae were much higher, reaching a peak of 21% of plants infested in the unsprayed plots of the first sowing date. Single applications of each insecticide reduced populations of S. avenae to zero. Some treatments, particularly in the early sown plots and those treated with pirimicarb, however, did allow some recolonisation, and thus led to increased virus incidence and decreased yields. Sprays applied before the end of the migration of S. avenae were more efficient at controlling BYDV if the insecticide was persistent, otherwise a spray after this period, in November, was more effective. Virus incidence, although reduced by sprays, was generally low in plots sown on 18 and 27 September. In contrast, about 11% of plants were infected in unsprayed plots sown on 6 September and a small yield benefit was obtained with insecticidal treatments. Enzyme-linked immunosorbent assay (ELISA) of plants taken from the plots indicated that MAV- and PAV-like strains were present, and were most likely to have been transmitted by S. avenae.     

Transmission of Pepino mosaic virus by the Fungal Vector Olpidium virulentus

Transmission of Pepino mosaic virus (PepMV) by the fungal vector Olpidium virulentus was studied in two experiments. Two characterized cultures of the fungus were used as stock cultures for the assay: culture A was from lettuce roots collected in Castellón (Spain), and culture B was from tomato roots collected in Murcia (Spain). These fungal cultures were maintained in their original host and irrigated with sterile water. The drainage water collected from irrigating these stock cultures was used for watering PepMV‐infected and non‐infected tomato plants to constitute the acquisition–source plants of the assay, which were divided into six different plots: plants containing fungal culture A (non‐infected and PepMV‐infected); plants containing fungal culture B (non‐infected and PepMV‐infected); PepMV‐infected plants without the fungus; and plants non‐infected either with PepMV and the fungus. Thirty‐six healthy plants grouped into six plots, which constituted the virus acquisition–transmission plants of the assay, were irrigated with different drainage waters obtained by watering the different plots of the acquisition–source plants. PepMV was only transmitted to plants irrigated with the drainage water collected from PepMV‐infected plants whose roots contained the fungal culture B from tomato with a transmission rate of 8%. No infection was detected in plants irrigated with the drainage water collected from plots with only a fungus or virus infection. Both the virus and fungus were detected in water samples collected from the drainage water of the acquisition–source plants of the assay. These transmission assays demonstrated the possibility of PepMV transmission by O. virulentus collected from tomato crops.     

Tomato yellow leaf curl virus from Sardinia is a whitefly-transmitted monopartite geminivirus.

The genome of an isolate of tomato yellow leaf curl virus from Sardinia, Italy (TYLCV-S), a geminivirus transmitted by the whitefly Bemisia tabaci, has been cloned and sequenced. The single circular DNA molecule comprises 2770 nucleotides. Genome organisation closely resembles that of the DNA A component of the whitefly-transmitted geminiviruses with a bipartite genome. A 1.8 mer of the TYLCV-S genome in a binary vector of Agrobacterium tumefaciens is infectious upon agroinoculation of tomato plants. Typical tomato yellow leaf curl disease symptoms developed about three weeks after inoculation. The disease was transmitted by the natural vector B.tabaci from agroinfected plants to test plants, reproducing in this way the full biological cycle and proving that the genome of TYLCV-S consists of only one circular single-stranded DNA molecule. Contrary to the other whitefly-transmitted geminiviruses described so far, there is no evidence for the existence nor the necessity of a second component (B DNA) in the TYLCV-S genome.     

烟粉虱在我国的发生为害现状及其非化学控制对策(英文)

烟粉虱 (BemisiatabaciGennadius )是热带、亚热带和温带地区主要害虫之一。烟粉虱早在 40年代在我国就已有记载 ,现广泛分布于我国的 2 2个省市。过去烟粉虱在我国为害并不严重 ,近年来在广东和北京等地已成为蔬菜和园艺作物生产的严重障碍。除直接为害外 ,烟粉虱可传播番茄和南瓜曲叶病等5种难于防治的病毒病。到目前为止 ,已报到 1 8种寄生性天敌、1 7种捕食性天敌及 1种虫生真菌。本文简要慨述烟粉虱在我国的发生为害与传毒现状 ,并结合我国的具体情况提出非化学控制烟粉虱的对策。     

Induced systemic resistance to tomato leaf curl virus and increased yield in tomato by plant growth promoting rhizobacteria under field conditions

The talc-based formulation of two Pseudomonas fluorescens strains (Pf1 and VPT10) and its mixture (with and without chitin) were tested against tomato leaf curl virus in tomato under greenhouse and field conditions. The mean percentage of tomato leaf curl virus infected plants were significantly lower (25%) with less symptom severity and delayed symptom expression up to nine additional days in Pseudomonas with chitin (VPT10 + chitin) treated tomato plants compared to non-bacterised control plants upon challenge inoculation with tomato leaf curl virus. Tomato leaf curl virus was partially purified and antiserum was developed. Using the antiserum the tomato leaf curl virus was detected in symptomatic leaves and in whitefly vector through direct antigen coating enzyme linked immunosorbent assay which revealed the low virus titre in Pseudomonas treated plants (VPT10 + chitin) and insect vector compared to untreated tomato plants. The results indicate the potentiality of plant growth promoting rhizobacteria strains and talc-powder formulations in the effective management of this tomato leaf curl virus in tomato under field conditions.     

Cover Caption

Asian citrus psyllid, Diaphorina citri Kuwayama, is vector of the bacterial pathogens causing huanglongbing. It occurs as three distinct color morphs in nature. Our results indicate that decreasing insecticide susceptibility among D. citri populations caused by over‐spraying is associated with increasing levels of detoxifying enzyme groups. Furthermore, orange/yellow morphs of this insect are more susceptible than blue/green and gray/brown color morphs suggesting that cuticular melanization may be a mechanism associated with development of resistance in this insect (see pages 843–852). Photo provided Tonya R. Weeks.     

Characterisation of pumpkin yellow vein mosaic virus from India

Yellow vein mosaic disease symptoms occur frequently in pumpkin in India. Diseased plants show vein yellowing, which sometimes coalesces to form chlorotic patches. Infected plants are stunted and flowers drop prematurely, greatly reducing yields. Diseased plants are infected by a begomovirus, designated pumpkin yellow vein mosaic virus (PYVMV), which is transmitted readily and in a persistent manner by the whitefly, Bemisia tabaci. Transmission of PYVMV requires minimum acquisition and inoculation access periods of 30 min and 10 min, respectively. The minimum latent period in the insect is 6 h and the virus persists in the vector for at least 8 days. PYVMV has a narrow host range consisting of a small number of cucurbit species and some tobacco cultivars. It was detected serologically in diseased plants and in viruliferous B. tabaci using polyclonal antibodies in a double‐antibody sandwich enzyme‐linked immunosorbent assay. Reactions with monoclonal antibodies in a triple‐antibody sandwich ELISA showed that PYVMV has an epitope profile distinct from those of other begomoviruses from the Indian sub‐continent. Polymerase chain reaction amplified fragments from the putative viral coat and movement protein genes. Based on comparative phylogeny of complete coat protein gene sequences, PYVMV was most similar to the bipartite Tomato leaf curl New Delhi virus from India and appears to be a new strain of this virus.     

Differential responses between a vector species Bemisia tabaci and a nonvector species Trialeurodes vaporariorum following ingestion of tomato yellow leaf curl virus

In transmitting plant viruses, insect vectors undergo physiological and behavioral alterations. The whitefly Bemisia tabaci is a vector of tomato yellow leaf curl virus (TYLCV), causing severe damages to various horticultural crop plants. To determine whether whitefly alteration is specific to vector species, the responses to TYLCV ingestion were compared between B. tabaci and Trialeurodes vaporariorum, a nonvector for TYLCV. The two species were reared on TYLCV‐infected and noninfected tomato, a host of TYLCV, and their longevity and fecundity were determined while rearing in either tomato or eggplant, a nonhost of TYLCV. TYLCV‐ingested B. tabaci increased their developmental rates but reduced fecundity when they were reared in either tomato or eggplant compared with those of TYLCV‐free ones. In contrast, TYLCV‐ingested T. vaporariorum did not show any of the aforementioned changes when reared on both plant species. In addition, TYLCV‐ingested B. tabaci increased their levels of three heat shock protein genes ( hsp20, hsp70, and hsp90) against thermal stress, whereas TYLCV‐ingested T. vaporariorum did not. The presence of TYLCV virions was identified in two colonies of both species via polymerase chain reaction analysis. TYLCV was detected in the whole body, saliva, and eggs of B. tabaci, while TYLCV was detected only in the whole body but not in the saliva and eggs of T. vaporariorum. The present results strongly indicated that TYLCV specifically manipulate physiological processes of the vector species, B. tabaci.     

Tomato yellow leaf curl geminivirus (TYLCV-Is) is transmitted among whiteflies (Bemisia tabaci) in a sex-related manner

Tomato yellow leaf curl virus (TYLCV) is the name given to a complex of geminiviruses infecting tomato cultures worldwide. TYLCV is transmitted by a single insect species, the whitefly Bemisia tabaci. Herein we show that a TYLCV isolate from Israel (TYLCV-Is) can be transmitted among whiteflies in a sex-dependent manner, in the absence of any other source of virus. TYLCV was transmitted from viruliferous males to females and from viruliferous females to males but not among insects of the same sex. Transmission took place when insects were caged in groups or in couples, in a feeding chamber or on cotton plants, a TYLCV nonhost. The recipient insects were able to efficiently inoculate tomato test plants. Insect-to-insect virus transmission was instrumental in increasing the number of whiteflies capable of infecting tomato test plants in a whitefly population. TYLCV was present in the hemolymph of whiteflies caged with viruliferous insects of the other sex; therefore, the virus follows, at least in part, the circulative pathway associated with acquisition from infected plants. Taken as a whole, these results imply that a plant virus can be sexually transmitted from insect to insect.     

Different transmission efficiencies may drive displacement of tomato begomoviruses in the fields in Taiwan

A progressive displacement of Tomato leaf curl Taiwan virus (ToLCTWV) by Tomato yellow leaf curl Thailand virus (TYLCTHV) from 2005 to 2009 has been recorded in tomato fields in Taiwan. Begomoviruses are exclusively transmitted by Bemisia tabaci complex, so we hypothesised that the displacement of tomato begomoviruses in the fields may be due to the invasion of a new virus/vector and the different transmission efficiencies of the viruses by the vectors. The objective of this research was to compare the transmission efficiency of TYLCTHV and ToLCTWV by the B and Q biotypes of B. tabaci complex. When transmission efficiency, virus retention in vector, and latent period for vector transmission were compared, the B biotype transmitted TYLCTHV and ToLCTWV more efficiently than did the Q biotype, and transmitted TYLCTHV more efficiently than ToLCTWV. The B biotype retained both viruses and remained infective throughout adulthood, but the Q biotype did not keep its infectivity, although it did retain both viruses lifelong. The B biotype transmitted TYLCTHV and ToLCTWV with the shortest latent period. In summary, B. tabaci B biotype and TYLCTHV is the best alliance for disease transmission, so we conclude that this may be one of drivers responsible for the displacement of ToLCTWV by TYLCTHV in tomato fields in Taiwan.