Situation of the whiteflies Bemisia tabaci and Trialeurodes vaporariorum in protected tomato crops in Algarve (Portugal)*

Protected tomato is the most important horticultural crop in the Algarve (south of Portugal). However, the growing area has decreased by almost 48% since 1995, mainly as a result of the pests Bemisia tabaci and Trialeurodes vaporariorum and the epidemics of Tomato yellow leaf curl virus (TYLCV), a Begomovirus transmitted by B. tabaci. Both whiteflies are vectors of economically important viruses. Recently, Tomato chlorosis virus (ToCV), a member of the genus Crinivirus, transmitted by both B. tabaci and T. vaporariorum, was reported infecting tomato crops in Algarve. A study was carried out to evaluate the dynamics of whitefly populations on tomato crops in Algarve. Population counts of B. tabaci were high in the first months of autumn, then decreased until January, when numbers of T. vaporariorum became higher. Counts of B. tabaci then increased again.     

Control of the Bemisia tabaci/Tomato yellow leaf curl virus complex on protected tomato crops in Algarve (Portugal)*

The whitefly Bemisia tabaci has been a serious pest in protected tomato crops since 1995 in the south of Portugal (Algarve), causing severe losses mainly resulting from Tomato yellow leaf curl virus (TYLCV), first reported in the autumn/winter season. In order to manage and control the B. tabaci/TYLCV complex, experimental field trials were carried out between 1997 and 2000. Several control methods were tested, such as the application of white screen nets to windows and doors, chemical treatments against B. tabaci and the use of cucumber as a trap crop. The results show that the percentage of plants with TYLCV symptoms mainly reflects B. tabaci infestation level in the first 6 weeks. Screen net protection was the control method that clearly provided a low incidence of plants with TYLCV symptoms in the autumn/winter season. Additionally, insecticide treatments, made weekly in the first 6 weeks, may give improved protection. In the winter/spring season, the B. tabaci/TYLCV complex is a minor problem because of the low populations of B. tabaci and the climatic conditions. Information about the work in progress and results was given to growers through visits to the experimental fields and oral presentations.     

Evidence of no horizontal or vertical transmission of tomato severe rugose virus by Bemisia tabaci MEAM1

Bemisia tabaci is important in agriculture worldwide, mainly because it is a vector of numerous plant viruses, probably the most important of which are members of the genus Begomovirus. Dozens of begomoviruses have been reported to infect tomato plants in Brazil, although tomato severe rugose virus (ToSRV) predominates in tomato crops. ToSRV, found so far only in Brazil, is efficiently transmitted by B. tabaci MEAM1. However, no studies have assessed the occurrence of vertical and horizontal transmission of the virus in the insect, which may have epidemiological consequences affecting disease management. This study evaluated the possibility of transmission of ToSRV between whiteflies during copulation and transovarial transmission from viruliferous females of B. tabaci MEAM1 to their progeny. Transmission of ToSRV did not occur during mating between males and females of B. tabaci MEAM1. Aviruliferous males and females confined with viruliferous insects of the opposite sex were also unable to transmit the virus to tomato plants. ToSRV was detected, by PCR, in the ovaries of viruliferous females of B. tabaci MEAM1 but not in eggs, nymphs, or adults of the progeny of viruliferous females. Adult progeny of viruliferous females also did not transmit ToSRV to tomato plants. Together, the results indicate that vertical and horizontal transmission of ToSRV by B. tabaci MEAM1 is unlikely. Sustainable management of the tomato golden mosaic disease caused by ToSRV should continue to focus on using resistant varieties, managing sources of inoculum around tomato fields, and rational chemical control of the vector.     

The transmission of geminiviruses by Bemisia tabaci

The cosmopolitan whitefly species, Bemisia tabaci (Gennadius) and Trialeurodes taporariorum (Westwood) have always been regarded as pests to a large range of worldwide crops. Both species are capable of transmitting plant viruses, with T. vaporariorum being the vector of only a few ‘clostero’-like viruses and B. tabaci the vector of viruses in several groups. The largest group of viruses transmitted by B. tabaci are the geminiviruses and B. tabaci is known to transmit around 60 members. Until recently, B. tabaci had been associated with only a limited range of host plants within any one region, although its total potential host range was large. Virus transmission was confined within the plant host range of each regional population of B. tabaci. The emergence of the polyphagous ‘B’ biotype of B. tabaci with its increased host range of more than 600 plant species, has resulted in geminiviruses infecting previously unaffected crops. As the ‘B’ biotype spreads further into Europe, European field and glasshouse crops have been shown to be susceptible to whitefly-transmitted viruses already endemic to other parts of the world. More than 20 colonies of B. tabaci, including both ‘B’ and non-‘B’ biotypes from disparate global locations have been compared for their ability to transmit more than 20 geminiviruses. All but two highly host-specific colonies were capable of transmitting most geminiviruses tested. However, some viruses were transmitted more efficiently than others. The virus coat protein or capsid is essential for vector recognition and transmission. By comparing transmissible viruses at the molecular level to viruses that are no longer whitefly-transmissible, the active epitope on the virus coat protein could be identified for designing future virus control strategies.     

烟粉虱传播的番茄褪绿病毒和番茄黄化曲叶病毒对不同番茄品种的复合侵染

为明确烟粉虱传播的番茄褪绿病毒(Tomato chlorosis virus,ToCV)与番茄黄化曲叶病毒(Tomato yellow leaf curl virus,TYLCV)对不同番茄品种的复合侵染情况,于2015年11月在山东省寿光市温室内采集13个番茄品种共390份疑似发病植株叶片,对不同番茄品种的TYLCV抗性和2种病毒的复合侵染以及温室内发病番茄植株上烟粉虱成虫的带毒率进行检测。结果表明,采集的13个番茄品种经分子标记检测鉴定均为TYLCV杂合抗性;不同番茄品种ToCV与TYLCV的复合侵染率存在明显差异,大果番茄粉宴和贝瑞上复合侵染率最高可达73.3%,而樱桃番茄八喜上未检测到这2种病毒的复合侵染。此外,在发病番茄植株上采集的烟粉虱成虫体内可检测到2种病毒,其中烟粉虱ToCV带毒率为90.7%,TYLCV带毒率为80.0%,同时检测到ToCV与TYLCV的概率为71.3%。表明ToCV和TYLCV的复合侵染在山东省番茄生产中普遍发生,烟粉虱可同时携带这2种病毒并广泛传播。     

Tomato chlorosis virus in pepper: prevalence in commercial crops in southeastern Spain and symptomatology under experimental conditions

Tomato chlorosis virus (ToCV), a member of the genus Crinivirus (family Closteroviridae), has been present in Spain since at least 1997, causing annual epidemics of yellowing in protected tomato crops. In 1999, sweet pepper plants exhibiting stunting and symptoms of interveinal yellowing and mild upward curling in the leaves, were found to be infected with ToCV in a greenhouse heavily infested with the whitefly Bemisia tabaci in the province of Almería, southeastern Spain. This study investigated the prevalence of ToCV in tomato and pepper crops in the major growing areas of southeastern Spain (Murcia, Almería and Málaga provinces) over a 3‐year period. In addition, an experimental system was developed for ToCV inoculation using B. tabaci as a vector, which allowed analysis of susceptibility of different pepper cultivars to the virus. The disease syndrome and yield losses induced by ToCV in pepper were also studied under experimental conditions, confirming severe yield reduction in infected plants.     

Note:Bemisia tabaci biotype B associated with tomato yellow leaf curl disease epidemics on rhodes Island, Greece

In 2006 an outbreak of tomato yellow leaf curl disease occurred in tomato crops on Rhodes Island, Greece. Diseased plants were found to be infested with the B biotype of theBemisia tabaci (Gennadius) complex and greenhouse and open-field-grown tomato crops were infected withTomato yellow leaf curl virus (TYLCV) introduced from the Middle East. This is the first report of TYLCV and the B biotype ofB. tabaci on Rhodes Island in Greece. http://www.phytoparasitica.org posting Dec. 11, 2007.     

<Emphasis Type="Italic">Physalis ixocarpa</Emphasis> and <Emphasis Type="Italic">P. peruviana</Emphasis>, new natural hosts of <Emphasis Type="Italic">Tomato chlorosis virus</Emphasis>

Tomato chlorosis virus causes yellow leaf disorder epidemics in many countries worldwide. Plants of Physalis ixocarpa showing abnormal interveinal yellowing and plants of Physalis peruviana showing mild yellowing collected in the vicinity of tomato crops in Portugal were found naturally infected with ToCV. Physalis ixocarpa and P. peruviana were tested for susceptibility to ToCV by inoculation with Bemisia tabaci, Q biotype. Results confirmed that ToCV is readily transmissible to both species. The infection was expressed in P. ixocarpa by conspicuous interveinal yellow areas on leaves that developed into red or brown necrotic flecks, while P. peruviana test plants remained asymptomatic. Infected plants of both P. ixocarpa and P. peruviana served as ToCV sources for tomato infection via B. tabaci transmission. This is the first report of P. ixocarpa and P. peruviana as natural hosts of ToCV.     

Lack of synergistic effects in tomato plants co-infected with tomato severe rugose virus and tomato chlorosis virus

The begomovirus Tomato severe rugose virus (ToSRV) and the crinivirus Tomato chlorosis virus (ToCV), in single and co-infections, are very common in tomato crops in Brazil. Both viruses are transmitted by the whitefly Bemisia tabaciMEAM1 (biotype B). The objective of this study was to analyse the interaction between ToSRV and ToCV in tomato plants of cultivars Santa Clara and Kada. Plants at 15, 30 and 45 days after emergence were inoculated with 30 viruliferous B. tabaci per plant. The following treatments were compared: plants inoculated with ToSRV, ToCV, ToSRV + ToCV, and healthy (control). The interaction between these viruses was analysed by measuring the virus titre by qPCR and the fresh and dry weights of the aerial parts of the tomato plants. Based on two independent assays, no significant effects for co-infection of ToSRV and ToCV on virus titres and plant development were observed compared to single infections. The dry weight of tomato plants of both cultivars infected with ToSRV, ToCV, or co-infected did not differ significantly. However, the dry weight of Santa Clara tomato plants infected with ToSRV, ToCV and ToSRV + ToCV showed mean reductions of 21.5%, 25.5% and 32%, respectively, compared to healthy plants, and mean reductions for Kada were 31.7%, 37.5% and 38%, respectively.     

山东寿光地区Q型烟粉虱对番茄褪绿病毒的传播

为明确山东寿光地区Q型烟粉虱对番茄褪绿病毒(Tomato chlorosis virus,To CV)感病流行的影响及其传毒特性,于2014年调查了该地区设施番茄上烟粉虱种群动态与To CV发病情况,利用特异引物对烟粉虱体内To CV进行了RT-PCR检测;并在室内测定了带毒Q型烟粉虱取食时间和种群数量对To CV感病株率的影响。结果表明,在番茄发病植株上采集的烟粉虱种群体内可检测到To CV;春茬番茄To CV发病株率随烟粉虱种群数量增加而逐渐升高,4—6月是To CV发生高峰期,6月22日发病株率达100%;秋茬番茄烟粉虱种群数量从10月下旬明显下降,而To CV发病株率升高,11月12日发病株率达100%;室内试验表明,To CV感病株率随着带毒Q型烟粉虱数量与取食时间的增加而明显升高。研究表明,Q型烟粉虱能有效传播To CV,且其种群数量对To CV发病株率存在显著影响,可通过防控烟粉虱以控制To CV的危害。     

Differentiation of three whitefly-transmitted geminiviruses from the Republic of Yemen

Three viruses collected in southern Yemen in 1990, infecting watermelon, tobacco and tomato were shown to be transmitted by the whiteflyBemisia tabaci and to have particle morphologies typical of geminiviruses. Colonies ofB. tabaci collected from different locations and from different hosts were used in virus transmission tests with the same host range of plants. Colonies established from both watermelon and cotton in the Yemen were identified as the squash silverleaf-inducing B biotype. The culture host of the colony did not influence virus acquisition and transmission efficiencies to and from other hosts. The tobacco and tomato geminiviruses had a similar host range, but differed in their severity in some hosts. Both these viruses differed from the watermelon geminivirus in host range and symptoms.Datura stramonium, an alternative host for all three viruses, could be co-infected by the watermelon and tobacco viruses.B. tabaci was able to acquire both viruses from the co-infectedD. stramonium and infect seedlings of either original host plant species with their respective viruses orD. stramonium with both. The viruses were identified as watermelon chlorotic stunt virus, tobacco leaf curl virus and tomato yellow leaf curl virus and were distinguished by cross hybridisation.     

Biological characterization of Tomato leaf curl New Delhi virus from Spain

Tomato leaf curl New Delhi virus (ToLCNDV; family Geminiviridae, genus Begomovirus) is an emerging virus in horticulture crops in Asia, and has recently been introduced in Spain, Tunisia and Italy. No betasatellite DNA was detected in infected tomato and zucchini squash samples from Spain, and agroinoculated viral DNA‐A and DNA‐B were sufficient to reproduce symptoms in plants of both crop species. Infected tomato and zucchini squash plants also served as inoculum sources for efficient transmission either mechanically or using Bemisia tabaci whiteflies. Cucumber, melon, watermelon, zucchini squash, tomato, eggplant and pepper, but not common bean, were readily infected using viruliferous whiteflies and expressed symptoms 8–15 days post‐inoculation. New full‐length sequences from zucchini squash and tomato indicated a high genetic homogeneity (>99% sequence identity) in the ToLCNDV populations in Spain, pointing to a single recent introduction event.     

First report of the Q biotype ofBemisia tabaci in Japan by mitochondrial cytochrome oxidase I sequence analysis

The recent upsurgence ofBemisia tabaci (Genn.) as an important insect pest and vector ofTomato yellow leaf curl virus (TYLCV) is directly linked to serious damage to tomato crops grown throughout Japan. The molecular genetic identification and phylogenetic relationships of 12B. tabaci populations collected from representative locations in Japan were determined based on the mitochondrial cytochrome oxidase I (mtCOI) sequence. Phylogenetic analysis of the whitefly mtCOI sequence indicated that both the invasive B and Q biotypes now occur in Japan. The Q biotype was found at four locations: Mihara in Hiroshima, Nishigoshi in Kumamoto, Miyanojo and Okuchi in Kagoshima prefectures; the remaining eight collections were identified as the B biotype. This is the first report of the introduction of Q biotype in Japan. http://www.phytoparasitica.org posting July 21, 2006.     

Panel of real‐time PCRs for the multiplexed detection of two tomato‐infecting begomoviruses and their cognate whitefly vector species

A new approach for the simultaneous identification of the viruses and vectors responsible for tomato yellow leaf curl disease (TYLCD) epidemics is presented. A panel of quantitative multiplexed real‐time PCR assays was developed for the sensitive and reliable detection of Tomato yellow leaf curl virus‐Israel (TYLCV‐IL), Tomato leaf curl virus (ToLCV), Bemisia tabaci Middle East Asia Minor 1 species (MEAM1, B biotype) and B. tabaci Mediterranean species (MED, Q biotype) from either plant or whitefly samples. For quality‐assurance purposes, two internal control assays were included in the assay panel for the co‐amplification of solanaceous plant DNA or B. tabaci DNA. All assays were shown to be specific and reproducible. The multiplexed assays were able to reliably detect as few as 10 plasmid copies of TYLCV‐IL, 100 plasmid copies of ToLCV, 500 fg B. tabaci MEAM1 and 300 fg B. tabaci MED DNA. Evaluated methods for routine testing of field‐collected whiteflies are presented, including protocols for processing B. tabaci captured on yellow sticky traps and for bulking of multiple B. tabaci individuals prior to DNA extraction. This work assembles all of the essential features of a validated and quality‐assured diagnostic method for the identification and discrimination of tomato‐infecting begomovirus and B. tabaci vector species in Australia. This flexible panel of assays will facilitate improved quarantine, biosecurity and disease‐management programmes both in Australia and worldwide.     

Pyriproxyfen,a novel insect growth regulator for controlling whiteflies: Mechanisms and resistance management

Pyriproxyfen, a novel juvenile hormone mimic, is a potent suppressor of embryogenesis and adult formation of the sweetpotato whitefly, Bemisia tabaci (Gennadius), and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Dipping of cotton or tomato seedlings infested with 0 to 1-day-old eggs in 0.1 mg litre^?1 resulted in over 90% suppression of egg hatch of both B. tabaci and T. vaporariorum. Older eggs were affected to a lesser extent. Exposure of whitefly females to cotton or tomato seedlings treated with pyriproxyfen resulted in oviposition of non-viable eggs. The LC90 values for egg viability of B. tabaci and T. vaporariorum exposed to treated plants were 0.05 and 0.2 mg litre^?1, respectively. Treatment of whitefly larvae with 0.04–5 mg litre^?1 resulted in normal development until the pupal stage; however, adult emergence was totally suppressed. Second instars of B. tabaci exposed to 5 mg litre^?1 pyriproxyfen, excreted honeydew at a level similar to the control level until the fourth instar (pupation), after which a strong reduction was observed. Inhibition of egg-hatch on the lower surface of cotton leaves was observed when their upper surface was treated with 1–25 mg litre^?1, indicating a pronounced translaminar effect. These findings indicate that pyriproxyfen is an efficient control agent of both B. tabaci and T. vaporariorum. The compound has been used successfully for controlling whiteflies in Israeli cotton fields since 1991. Adults of B. tabaci collected from a rose greenhouse and from adjacent cotton fields were monitored during 1991–1993 for their susceptibility to pyriproxyfen. A high level of resistance was recorded in whiteflies collected from a greenhouse after three successive applications of pyriproxyfen. Based on LC50 values, the resistance ratio for egg-hatch suppression was 554-fold and, for adult emergence failure, 10-fold. However, a single treatment of pyriproxyfen in cotton fields during the summer season (according to an insecticide resistance management (IRM) strategy) did not alter appreciably the susceptibility of B. tabaci to this compound. In order to prevent development of resistance, an attempt should be made to restrict its use to one treatment per crop season applied during the peak activity of the pest. Pyriproxyfen can be alternated with other novel compounds such as buprofezin and diafenthiuron for controlling whiteflies in cotton, vegetables and ornamentals as part of integrated pest management (IPM) and IRM strategies. In pyriproxyfen- or buprofezin-resistant strains of B. tabaci or T. vaporariorum, no appreciable cross-resistance was observed among pyriproxyfen, buprofezin and diafenthiuron.     

Tomato infectious chlorosis virus — a new clostero-like virus transmitted byTrialeurodes vaporariorum

A previously undescribed virus disease of tomato, other crops and weed hosts was found in California. Affected tomato plants exhibited interveinal yellowing, necrosis and severe yield losses. Leaf dips and purified preparations contained closterovirus-like long flexuous, filamentous particles approximately 12×850–900 nm. The virus, designated as tomato infectious chlorosis virus (TICV), is transmitted in a semipersistent manner by the greenhouse whitefly,Trialeurodes vaporariorum. The host range of the virus is moderate (26 species in 8 plant families) but includes some important crops and ornamental species including tomato, (Lycopersicon esculentum), tomatillo (Physalis ixocarpa), potato (Solanum tuberosum), artichoke (Cynara scolymus), lettuce (Lactuca sativa) and petunia (Petunia hybrida). The virus has been found in a number of different locations in California and has a number of potential vehicles of movement including greenhouse grown ornamentals, tomato transplants, artichoke cuttings and potato seed. The virus has the potential to spread to other growing regions with resident populations of the greenhouse whitefly. The host range, particle size, insect transmission, and serology clearly distinguish TICV from previously described viruses.     

First record of the Q Biotype of the sweetpotato whitefly, Bemisia tabaci, intercepted in the UK

For the UK, Bemisia tabaci poses a threat primarily to protected vegetable crops due to the transmission of several plant-pathogenic viruses. There are at least 24 different biotypes of B. tabaci that cannot be differentiated through morphological traits. The B (Middle East-Asia Minor 1 species) and Q (Mediterranean species) biotypes are widely considered to be the most important and, as such, the ability to rapidly and precisely biotype B. tabaci interceptions is vital when developing effective control strategies. Intercepted adult/pupal B. tabaci received from the UK Plant Health and Seeds Inspectorate (PHSI) during 2002–2003 (n?=?60) and 2010–2011 (n?=?42) were both biotyped and tested for the presence of Tomato yellow leaf curl virus (TYLCV) and Tomato yellow leaf curl Sardinia virus (TYLCSV) using a real-time PCR assay based on TaqMan? chemistry. The positive results indicated that during 2002–2003 the Q biotype comprised 68.3?% of the interceptions whilst in 2010–2011 it comprised 66.7?% of the B. tabaci samples intercepted. Only three of the B biotypes collected during 2002–2003 were positive for TYLCSV, two originating from Israel and the other of unknown origin. The implications in regards to pest management of the insect are discussed.     

日光温室番茄褪绿病毒病的发生规律及其与Q型烟粉虱种群动态关系

为有效控制日光温室番茄褪绿病毒病,于2014—2015年通过RT-PCR检测方法研究了济南市日光温室番茄褪绿病毒(Tomato chlorosis virus,ToCV)的发生规律、其与Q型烟粉虱Bemisia tabaci种群动态的关系及防虫网对该病毒病的防控效果。结果表明,春季日光温室番茄植株上Q型烟粉虱成虫数量呈增长趋势,5月下旬最高达到0.10头/叶,秋季日光温室番茄植株上Q型烟粉虱成虫数量9月上旬达最高7.42头/叶,后逐渐下降;日光温室Q型烟粉虱带毒率随着定植时间的延长而逐渐上升,之后维持相对稳定状态,即春季为20.00%~24.14%,秋季为30.00%~40.00%。日光温室ToCV发生与Q型烟粉虱成虫数量和带毒率密切相关,春季番茄最高发病率为12.00%;秋季番茄植株最高发病率为93.02%。番茄育苗和生长期用100目防虫网隔离可显著降低番茄植株带毒率。因此,秋季是日光温室ToCV防控关键期,覆盖防虫网阻隔烟粉虱可有效防治ToCV,推荐在日光温室使用。     

Microsatellites reveal widespread predominance of an invasive over an indigenous <Emphasis Type="Italic">Bemisia tabaci</Emphasis> in Venezuela

The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is an important pest due to its capacity for producing strong infestations and transmitting plant viruses. The New World putative species of B. tabaci complex (NW) is the indigenous whitefly of the Americas, but only the invasive Middle East-Asia Minor 1 putative species of B. tabaci complex (MEAM1), commonly referred to as the “B biotype” was identified in a limited scope sampling in Venezuela. Similarly to MEAM1 invasions elsewhere, in this South American country there has been an increase in the geographic range and abundance of B. tabaci, and in the number of viruses that it transmits since the late 1980s. We estimated the diversity of B. tabaci to elucidate their role in the epidemiology of geminiviruses in Venezuela. Thirteen microsatellite loci were screened in samples collected from 19 localities in ten major agricultural states. A Bayesian clustering method (Structure) grouped the samples into two genetic groups. Control samples from whiteflies NW and MEAM1 and partial sequencing of the mitochondrial cytochrome oxidase I gene showed that our samples of B. tabaci populations from Venezuela fall within NW and MEAM1 groups. In this survey, MEAM1 was predominant over NW whitefly in a proportion of 35:1. No evidence was observed for gene flow between indigenous and invader whitefly. Altogether, our results stress the urgency for controlling the proliferation of the invasive whitefly.