Discovering new insect viruses: whitefly iridovirus (Homoptera: Aleyrodidae: Bemisia tabaci)

Adult whiteflies, Bemisia tabaci (Gennadius), collected from the field were screened for viral pathogens using a cell line from the silverleaf whitefly, B. tabaci, B biotype (syn. B. argentifolii). Homogenates from the field-collected whiteflies were applied to cell cultures and checked for cytopathic effects (CPE). Cells were observed to develop cytoplasmic inclusions and to have a change in morphology. Cells displaying CPE were observed using a transmission electron microscope and found to be infected with a virus. The virus particles had an icosahedral shape and an approximate size of 120-130 nm. The virus was observed in defined areas of the cytoplasm adjacent to the cell nucleus. Analysis using polymerase chain reaction, Southern blot hybridization, and DNA sequencing confirmed that the virus discovered infecting the whitefly cell cultures was an iridovirus. Sequence analysis showed that the amplimer (893 bp) had a 95% homology to the invertebrate iridescent virus type 6 major capsid protein gene. Discovery of new viruses of whiteflies may provide renewed interest in using pathogens in the development of innovative management strategies. This is the first report of an iridescent virus isolated from whiteflies, B. tabaci, collected from the field.     

kdr突变和解毒代谢在B型烟粉虱对高效氯氰菊酯抗性中的作用

本研究明确了kdr突变和解毒代谢在B型烟粉虱Bemisia tabaci对高效氯氰菊酯抗性中的作用。B型烟粉虱NJ品系相对于烟粉虱敏感品系（SUD-S,非B型）对高效氯氰菊酯有266倍的抗性。对NJ品系用高效氯氰菊酯进行群体筛选获得抗性为811倍的NJ-R1品系,对NJ品系进行单对交配筛选获得抗性达2 634倍的NJ-R2品系。在NJ,NJ-R1和NJ-R2品系间,酯酶、多功能氧化酶和谷胱甘肽S-转移酶活性无显著差异,说明在筛选过程中解毒代谢没有发生变化。PASA检测结果表明,NJ-R2品系钠离子通道基因L925I突变（kdr突变）频率为100%,NJ-R1品系为80.6%,NJ品系为55%。由此可见,kdr突变频率的增加是B型烟粉虱种群对高效氯氰菊酯抗性上升的主要原因。在NJ,NJ-R1和NJ-R2品系中,增效醚（PBO）对高效氯氰菊酯的增效作用均为20倍左右,而PBO对SUD-S品系没有任何增效作用。PBO能同时抑制烟粉虱的多功能氧化酶和酯酶,通过与TPP增效作用进行对比表明,在B型烟粉虱中PBO所产生的增效作用主要来源于对酯酶的抑制。因此,B型烟粉虱品系（NJ-R2,NJ-R1和NJ）与非B型SUD-S品系相比存在20倍左右的先天抗性,该先天抗性主要与B型烟粉虱的特有酯酶有关。在B型烟粉虱品系对高效氯氰菊酯的抗性中,抗性水平完全由kdr突变频率高低所决定。     

Dynamics of resistance to the neonicotinoids acetamiprid and thiamethoxam in Bemisia tabaci (Homoptera: Aleyrodidae)

The dynamics of resistance in the sweetpotato whitefly, Bemisia tabaci (Gennadius), to the neonicotinoids acetamiprid and thiamethoxam was studied extensively in cotton fields in Israel during the cotton-growing seasons 1999-2003. Whitefly strains were collected in early and late seasons mainly in three locations in northern, central, and southern Israel. The whiteflies were assayed under laboratory conditions for susceptibility to neonicotinoids, as part of the Israeli cotton insecticide resistance management strategy. Selections to both acetamiprid and thiamethoxam and cross-resistance between them also were conducted in the laboratory. Although no appreciable resistance to acetamiprid was observed up to 2001, a slight increase of approximately five-fold resistance was detected during 2002 and 2003. However, from 2001 to 2003 thiamethoxam resistance increased >100-fold in the Ayalon Valley and Carmel Coast cotton fields. In cross-resistance assays with both neonicotinoids, the strain that had been selected with thiamethoxam for 12 generations demonstrated almost no cross-resistance to acetamiprid, whereas the acetamiprid-selected strain exhibited high cross-resistance of >500-fold to thiamethoxam.     

Extraordinary resistance to insecticides reveals exotic Q biotype of Bemisia tabaci in the New World

A strain of the whitefly Bemisia tabaci (Gennadius) possessing unusually high levels of resistance to a wide range of insecticides was discovered in 2004 in the course of routine resistance monitoring in Arizona. The multiply resistant insects, collected from poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) plants purchased at a retail store in Tucson, were subjected to biotype analysis in three laboratories. Polyacrylamide gel electrophoresis of naphthyl esterases and sequencing of the mitochondrial cytochrome oxidase I gene (780 bp) confirmed the first detection of the Q biotype of B. tabaci in the New World. This U.S. Q biotype strain, referred to as Poinsettia'04, was highly resistant to two selective insect growth regulators, pyriproxyfen and buprofezin, and to mixtures of fenpropathrin and acephate. It was also unusually low in susceptibility to the neonicotinoid insecticides imidacloprid, acetamiprid, and thiamethoxam, relative to B biotype whiteflies. In 100 collections of whiteflies made in Arizona cotton (Gossypium spp.), vegetable, and melon (Cucumis melo L.) fields from 2001 to 2005, no Q biotypes were detected. Regions of the United States that were severely impacted by the introduction of the B biotype of B. tabaci in the 1980s would be well advised to promote measures that limit movement of the Q biotype from controlled environments into field systems and to formulate alternatives for managing this multiply-resistant biotype, in the event that it becomes more widely distributed.     

Upregulation of temperature susceptibility in Bemisia tabaci upon acquisition of Tomato yellow leaf curl virus (TYLCV)

Acquisition of plant viruses has various effects on physiological mechanisms in vector insects. Bemisia tabaci is the only known vector of Tomato yellow leaf curl virus (TYLCV), which is a serious virus affecting tomato cultivars. In this study, the lifespan of Q1 biotype was compared between non-viruliferous (NV) and TYLCV-viruliferous (V) whiteflies. Total lifespan from egg to adult death of NV whiteflies was 62.54days but 10.64days shorter in V whiteflies. We investigated the temperature susceptibility of B. tabaci by comparing mortalities as well as heat shock protein (hsp) mRNA levels between NV and V whiteflies. For this, NV and V whiteflies were exposed for either 1 or 3h at 4, 25, and 35°C. The mortality of V whiteflies was higher than NV ones following exposure at either 4 or 35°C, but there was no significant difference at 25°C. Analysis of the expression level of heat shock protein (hsp) genes using quantitative real-time PCR showed that both cold and heat shock treatments stimulated higher expression of hsps (hsp40, hsp70, and hsp90) at various rates in V whiteflies than NV ones, but there was no difference at 25°C. All together, our results show that TYLCV acquisition accelerated the developmental rate and increased susceptibility to thermal stress in B. tabaci. Therefore, this modification may result in reduced vector longevity due to increased metabolic energy utilization. Our results provide insights into the complex interaction between vector fitness and thermal stress in relation to the acquisition and transmission of plant viruses.     

Establishment of a silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) population in western Sydney

A field survey in western Sydney found populations of Bemisia tabaci biotype B (silverleaf whitefly) that have the potential to damage greenhouse vegetable crops prevalent in the region. Adult whiteflies were collected from five farms at 2-week intervals and the proportion of silverleaf whitefly in the overall whitefly population was determined using polyacrylamide gel electrophoresis. High levels of silverleaf whitefly were detected at most sampling dates on two of the farms surveyed and a third farm exhibited lower but relatively continuous silverleaf whitefly abundance. The presence of permanent silverleaf whitefly populations must be considered by the greenhouse industry when formulating whitefly management plans for western Sydney.     

喷施吲哚-3-乙酸 (IAA) 对番茄及其上B型烟粉虱的影响

【目的】不同植物生长调节物质对植食性昆虫产卵、发育、取食等常有促进或抑制作用,进而影响植物与昆虫的互作关系。本研究旨在阐明常用的植物生长调节剂吲哚-3-乙酸对B型烟粉虱Bemisia tabaci (Gennadius)的影响,进而探索防治烟粉虱环境友好的方法,同时期望获得更加优质的烟粉虱用作替代寄主饲养寄生蜂。【方法】对番茄 Solanum lycopersicum L.植株外源喷施吲哚-3-乙酸(IAA),检测其生理生化的响应;记录B型烟粉虱存活率、产卵量并测量解毒酶等指标。【结果】喷施IAA后番茄叶片含水量略有上升,叶面积增大,叶绿素含量增加,过氧化物酶(POD)活性降低,多酚氧化酶(PPO)活性升高,超氧化物歧化酶(SOD)活性变化不显著(P＞0.05)。喷施IAA后番茄上B型烟粉虱成虫存活率高于对照组,其中50 mg/L IAA番茄上B型烟粉虱成虫存活率和总产卵量最高,250 mg/L IAA存活率最低;喷施IAA 120 h后烟粉虱总产卵量升高;碱性磷酸酶(AKP)、超氧化物歧化酶(SOD)活性较对照升高。【结论】喷施不同浓度的IAA溶液后,番茄植株的生理生化水平发生不同程度的改变,烟粉虱成虫的存活状况、产卵量以及体内解毒活性也会产生不同程度的改变。适宜剂量的IAA处理能够使烟粉虱的生存表现更加优异,从而为饲养寄生蜂提供优质的替代寄主。     

B型烟粉虱与温室白粉虱不同虫态的碱性磷酸酶性质比较

为了探明B型烟粉虱Bemisia tabaci B-biotype 和温室白粉虱Trialeurodes vaporariorum体内的碱性磷酸酶(alkaline phosphatase,ALP)在两者竞争替代中所起的作用,以对硝基苯磷酸二钠 (pNPP)为底物,采用个体测定和群体测定的方法,研究比较了2种粉虱不同虫态中该酶的性质。结果表明：2种粉虱的碱性磷酸酶比活力在整个发育历期均逐渐增加,成虫期达到最大。温室白粉虱2至4龄若虫（伪蛹）期的碱性磷酸酶比活力分别是B型烟粉虱对应龄期酶比活力的2.58、2.68和3.14倍; B型烟粉虱雌雄成虫的碱性磷酸酶比活力分别是温室白粉虱雌雄成虫酶比活力的1.24和1.26倍,且2种粉虱雌虫的酶比活力显著大于其雄虫。2种粉虱2龄若虫到成虫的碱性磷酸酶最适pH均为7.8,最适温度均为47℃;在1龄若虫中均未能检测到该酶活性。测定并比较2种粉虱不同虫态碱性磷酸酶动力学特征参数的结果显示,温室白粉虱碱性磷酸酶在3、4龄若虫的亲和力以及在2, 3, 4龄若虫的酶蛋白浓度均显著大于B型烟粉虱的对应值,而在成虫期2种粉虱的亲和力、酶蛋白浓度无差异,B型烟粉虱的活化能显著小于温室白粉虱。据此推测,B型烟粉虱利用碱性磷酸酶在若虫期进行组织骨化和生长发育不如温室白粉虱,但羽化为成虫后利用其进行解毒代谢则可能强于温室白粉虱。     

烟粉虱(Bemisia tabaci)的寄主选择性

通过田间系统调查、实验室嗅觉测定、笼内和培养皿内自由扩散观察,对烟粉虱的寄主选择性进行了研究.结果表明,在田间,烟粉虱对不同的寄主植物存在明显的寄主选择性,其中对茄子、花椰菜、黄瓜等植物具有较强的嗜性,而对蕹菜、芹菜、苋菜等植物的嗜性较差;烟粉虱对同一植物的不同品种也有明显的选择性.烟粉虱对寄主植物颜色有明显的选择性,选择结果与烟粉虱对这些寄主的嗜性趋势基本一致.烟粉虱对单株寄主植物的嗅觉反应不敏感,但对植物叶片的乙醇抽提物有明显的嗅觉反应,并表现出较强的寄主选择性.在养虫笼内,烟粉虱从虫源皿向寄主植物自由扩散的过程中,在不同寄主植物和同一植物的不同品种上着落的成虫数量不同,并且在一定的时间范围内,着落在寄主叶片上的虫量还会不断的发生变化.     

辽宁省冬季温室内越冬粉虱伪蛹的种类鉴定及烟粉虱体内番茄黄化曲叶病毒的检测

为了揭示辽宁省冬季温室内越冬粉虱伪蛹的种类及烟粉虱Bemisia tabaci （Gennadius）携带番茄黄化曲叶病毒（tomato yellow leaf curl virus, TYLCV）情况, 于2012年1月份在辽宁省不同县市区的温室作物上采集了17份粉虱伪蛹样品（每样品含30头粉虱伪蛹） , 镜检鉴别粉虱种类并利用mtCOI基因对烟粉虱生物型进行了鉴定; 检测了烟粉虱携带TYLCV情况并对其PCR扩增产物进行了测序分析。结 果表明： 辽宁省冬季温室内存在越冬温室白粉虱Trialeurodes vaporariorum （Westwood）与烟粉虱。17份粉虱样品中, 11份样品为烟 粉虱样品, 6份样品为温室白粉虱和烟粉虱混合样品。混合样品中, 温室白粉虱仅在锦州凌海（LH）样品中占优势。17份烟粉虱样品（包 括混合样品）中, 仅有4份样品为B型与Q型混合样品, 其他13份样品烟粉虱生物型均为Q型。17份烟粉虱样品中有3份Q型烟粉虱样品检测 到TYLCV, 系统树分析进一步证实该病毒是TYLCV。调查结果为辽宁省粉虱与TYLCV的早期测报和防控提供了科学依据。     

Species within the Bemisia tabaci (Hemiptera: Aleyrodidae) complex in soybean and bean crops in Argentina

The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex that contains some of the most damaging pests in tropical and subtropical regions. Recent studies suggested that this complex is composed of at least 24 distinct species. We use the approach from these studies to consider the identity of B. tabaci in Argentina. Previous studies have suggested the presence of a B. tabaci presumably indigenous to the Americas and referred to as the BR biotype in Argentina. We placed the entity referred to as the BR biotype within the B. tabaci cryptic species complex using whiteflies collected in soybean and bean crops in northern and central Argentina. The whiteflies were assigned using the mitochondrial cytochrome oxidase (mtCOI) gene. Four unknown haplotypes plus two Argentina sequences from GenBank formed a cluster that was basal to the rest of the New World sequences. These sequences diverged from the consensus sequence across the range of 3.6 to 4.3%. Applying the species assignment rules of recent studies suggests that the individuals from Argentina form a separate species. A fifth unknown haplotype fell within the New World putative species and formed a distinct cluster with haplotypes from Panama. These results suggest that Argentina has two indigenous species belonging to the B. tabaci cryptic species complex. Rather than using mtCOI sequencing for all B. tabaci collected, a simple random amplified polymorphic DNA-polymerase chain reaction diagnostic was used and tested along with previously published primers designed to work specifically with the BR biotype from Brazil. These primers were either unable to distinguish between the two indigenous members of the complex in Argentina or indicated a difference when none was evident on the basis of mtCOI sequence comparison.     

Baseline susceptibility of Bemisia tabaci B biotype (Hemiptera: Aleyrodidae) populations from California and Arizona to spiromesifen

Susceptibility to spiromesifen, a tetronic acid derivative, was determined for three imidacloprid-resistant strains and 12 geographically discrete natural populations of Bemisia tabaci (Gennadius) (=Bemisia argentifolii Bellows & Perring) (Hemiptera: Aleyrodidae) from California and Arizona by laboratory bioassays. Newly emerged first instars were sprayed with aqueous serial dilutions of spiromesifen and evaluated for toxicity to establish baseline susceptibility data. Interpopulation variability in susceptibility to spiromesifen was observed among the natural populations of whiteflies up to 29-fold; however, there was only 30-fold difference in susceptibility among natural and resistant populations tested. In general, spiromesifen was quite toxic to first instars across most of their geographic range, with LC50 values ranging from 0.210 to 6.08 microg (AI)/ml. The magnitude of variation was smaller among the three-resistant strains. These results suggest that the observed variability reflect natural variation in spiromesifen susceptibility among all the test populations, possibly due to previous exposure to insecticides at each location. The effectiveness of spiromesifen also was evaluated against all immature stages of whiteflies from three field and two resistant strains. Spiromesifen was significantly more active against early instars of whiteflies based on lower LC50 values recorded compared with the fourth instars. Spiromesifen was effective against the resistant strains including a Q-biotype of B. tabaci from Spain, which is highly resistant to neonicotinoids. Results of this study indicate absence of cross-resistance between spiromesifen and more commonly used neonicotinoids. Our findings suggest that spiromesifen should be considered an ideal candidate for whitefly resistance management programs in rotation with other effective chemistries.     

西藏发现Q型烟粉虱

【目的】调查西藏自治区烟粉虱Bemisia tabaci(Gennadius)的发生情况。【方法】从西藏拉萨采集到烟粉虱各个虫态,采用3D数码显微镜观察所采集烟粉虱的形态特征,利用mt COⅠ分子标记检测烟粉虱的生物型。【结果】明确并详细描述了烟粉虱各形态特征,mt COⅠ分子标记检测显示西藏采集到的烟粉虱为Q生物型。【结论】在形态学鉴定的基础上,分子生物学鉴定该粉虱为Q型烟粉虱,这是Q型烟粉虱在西藏自治区发生的首次报道。     

Distribution of Bemisia tabaci (Hemiptera: Aleyrodidae) biotypes in North America after the Q invasion

After the 2004 discovery of the Bemisia tabaci (Gennadius) (Hemiptera Aleyrodidae) Q biotype in the United States, there was a vital need to determine the geographical and host distribution as well as its interaction with the resident B biotype because of its innate ability to rapidly develop high-level insecticide resistance that persists in the absence of exposure. As part of a coordinated country-wide effort, an extensive survey of B. tabaci biotypes was conducted in North America, with the cooperation of growers, industry, local, state, and federal agencies, to monitor the introduction and distribution of the Q biotype. The biotype status of submitted B. tabaci samples was determined either by polymerase chain reaction amplification and sequencing of a mitochondrial cytochrome oxidase I small subunit gene fragment and characterization of two biotype discriminating nuclear microsatellite markers or esterase zymogram analysis. Two hundred and eighty collections were sampled from the United States, Bermuda, Canada, and Mexico during January 2005 through December 2011. Host plants were split between ornamental plant and culinary herb (67%) and vegetable and field crop (33%) commodities. The New World biotype was detected on field-grown tomatoes (Solanum lycopersicum L.) in Mexico (two) and in commercial greenhouses in Texas (three) and represented 100% of these five collections. To our knowledge, the latter identification represents the first report of the New World biotype in the United States since its rapid displacement in the late 1980s after the introduction of biotype B. Seventy-one percent of all collections contained at least one biotype B individual, and 53% of all collections contained only biotype B whiteflies. Biotype Q was detected in 23 states in the United States, Canada (British Columbia and Ontario territories), Bermuda, and Mexico. Forty-five percent of all collections were found to contain biotype Q in samples from ornamentals, herbs and a single collection from tomato transplants located in protected commercial horticultural greenhouses, but there were no Q detections in outdoor agriculture (vegetable or field crops). Ten of the 15 collections (67%) from Canada and a single collection from Bermuda contained biotype Q, representing the first reports of biotype Q for both countries. Three distinct mitochondrial haplotypes of B. tabaci biotype Q whiteflies were detected in North America Our data are consistent with the inference of independent invasions from at least three different locations. Of the 4,641 individuals analyzed from 517 collections that include data from our previous work, only 16 individuals contained genetic or zymogram evidence of possible hybridization of the Q and B biotypes, and there was no evidence that rare hybrid B-Q marker co-occurrences persisted in any populations.     

Assessment of cross-resistance potential to neonicotinoid insecticides in Bemisia tabaci (Hemiptera: Aleyrodidae)

Laboratory bioassays were carried out with four neonicotinoid insecticides on multiple strains of Bemisia tabaci (Gennadius) to evaluate resistance and cross-resistance patterns. Three imidacloprid-resistant strains and field populations from three different locations in the southwestern USA were compared in systemic uptake bioassays with acetamiprid, dinotefuran, imidacloprid and thiamethoxam. An imidacloprid-resistant strain (IM-R) with 120-fold resistance originally collected from Imperial Valley, California, did not show cross-resistance to acetamiprid, dinotefuran or thiamethoxam. The Guatemala-resistant strain (GU-R) that was also highly resistant to imidacloprid (RR=109-fold) showed low levels of cross-resistance when bioassayed with acetamiprid and thiamethoxam. However, dinotefuran was more toxic than either imidacloprid or thiamethoxam to both IM-R and GU-R strains as indicated by low LC50s. By contrast, a Q-biotype Spanish-resistant strain (SQ-R) of B. tabaci highly resistant to imidacloprid demonstrated high cross-resistance to the two related neonicotinoids. Field populations from Imperial Valley (California), Maricopa and Yuma (Arizona), showed variable susceptibility to imidacloprid (LC50s ranging from 3.39 to 115 microg ml(-1)) but did not exhibit cross-resistance to the three neonicotinoids suggesting that all three compounds would be effective in managing whiteflies. Yuma populations were the most susceptible to imidacloprid. Dinotefuran was the most toxic of the four neonicotinoids against field populations. Although differences in binding at the target site and metabolic pathways may influence the variability in cross-resistance patterns among whitefly populations, comparison of whitefly responses from various geographic regions to the four neonicotinoids indicates the importance of ecological and operational factors on development of cross-resistance to the neonicotinoids.     

辣椒碱对烟粉虱的生物活性及生长发育和生殖力的影响

在实验室条件下研究了辣椒碱对烟粉虱的生物活性及生长发育和生殖力的影响.结果表明:辣椒碱对烟粉虱各虫态均有杀虫活性,且随辣椒碱浓度的增大活性增强;辣椒碱浸叶法/浸虫法处理对烟粉虱成虫、卵和若虫的毒力(LC50分别为3525.79、1603.29和1526.27mg·L-1))均高于内吸法处理(LC50分别为5360.04、2359.19和5897.43 mg.L-1),两种处理方法下辣椒碱对烟粉虱卵的毒力均明显高于对成虫的毒力;2000和4000 mg·L-1浓度辣椒碱对烟粉虱成虫具有明显的拒食作用,烟粉虱在该两种浓度辣椒碱处理过的棉花叶上取食24 h的蜜露分泌量均显著低于取食非处理棉花叶后的蜜露分泌量;辣椒碱各试验浓度对烟粉虱成虫均表现出较强的产卵忌避作用,当辣椒碱处理浓度达4000 mg·L-1时,对烟粉虱的选择性产卵忌避率和非选择性产卵忌避率分别高达94.2％和83.0％.500、1000和2000 mg·L-1辣椒碱浸渍处理对烟粉虱存活卵和若虫的发育历期、成虫羽化率均没有影响,但辣椒碱4000mg·L-1处理明显延长烟粉虱若虫发育历期、降低成虫羽化率.不同浓度辣椒碱处理均明显抑制烟粉虱生殖力,且这种抑制作用随辣椒碱浓度的增大而增强.     

Transmission of tomato leaf curl geminiviruses by Bemisia tabaci: effects of virus isolate and vector biotype

Cultures of Bemisia tabaci from Ivory Coast (IC), Pakistan (PK) and USA (US B-type) were compared for the frequency with which they transmitted three tomato geminivirus isolates: Indian tomato leaf curl virus from Bangalore (ITmLCV), and tomato yellow leaf curl viruses from Nigeria (TYLCV-Nig) and Senegal (TYLCV-Sen). Frequency of transmission from tomato to tomato depended both on the whitefly culture and the virus isolate. US B-type and IC whiteflies transmitted TYLCV-Sen more frequently than ITmLCV whereas PK whiteflies transmitted ITmLCV more frequently than TYLCV-Sen. US B-type whiteflies transmitted both viruses four to nine times more frequently than IC whiteflies. TYLCV-Nig was transmitted rarely by US B-type and not at all by IC whiteflies. Previous work indicates that the geminivirus coat protein controls vector transmissibility. The differential adaptation of TYLCV-Sen to transmission by US B-type whiteflies and of ITmLCV to PK whiteflies was associated with a large difference in epitope profile of the coat proteins of the two viruses. Also, the readily transmissible TYLCV-Sen differed appreciably in epitope profile from the poorly transmissible TYLCV-Nig, which reached a consistently greater concentration in source tissues but lacked epitope 18. However, the lack of epitope 18 in ITmLCV did not prevent its transmission by US B-type whiteflies. Differences in frequency and specificity of geminivirus transmission by whitefly cultures from different countries therefore were associated with differences among epitope profiles of the coat proteins of the viruses, but the structural features of the proteins that control transmission remain to be determined.     

Identification of biochemical markers linked to neonicotinoid cross resistance in Bemisia tabaci (Hemiptera: Aleyrodidae)

The whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), is a serious pest in many cropping systems world-wide and occurs in different biotypes. The most widespread one is the B-type, whereas the Q-biotype is nowadays still mostly restricted to Southern Spain. Neonicotinoid cross-resistance is known at a high level in Q-types from Spain and individual samples collected in Italy and Germany. Now we detected for the first time high neonicotinoid cross-resistance in a B-type from Israel. Target site resistance to imidacloprid using [(3)H]imidacloprid in nicotinic acetylcholine receptor (nAChR) binding assays could not be detected in any of these highly resistant strains. The impact of metabolizing enzymes such as esterases, glutathione S-transferases, and cytochrome P450-dependent monooxygenases in neonicotinoid resistance was studied biochemically with artificial substrates. Monooxygenase activity was increased 2-3-fold in moderately resistant strains (RF approximately 30) and even 5-6-fold in highly resistant strains (RF approximately 1,000). Only monooxygenase activity correlated with imidacloprid, thiamethoxam and acetamiprid resistance and, therefore, monooxygenases seem to be the only enzyme system responsible for neonicotinoid resistance in B. tabaci Q- and B-types. The oxidative degradation of imidacloprid in resistant Q-type strains could be confirmed by metabolism studies of [(14)C]imidacloprid in vivo. Five-hydroxy-imidacloprid could be detected as the only main metabolite. The insecticidal activity and binding affinity to nAChR of this compound was 10 times lower than imidacloprid itself in 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.     

Bemisia tabaci (Homoptera: Aleyrodidae) biotypes in India

Host plant performance, esterase, and virus transmission tests revealed cassava-strain and sweetpotato-strain populations of whitefly Bemisia tabaci (Gennadius) biotypes in India. Individuals from the sweetpotato-reared population did not breed on cassava, Manihot esculenta Crantz, and the cassava-strain-reared individuals failed to develop on sweetpotato, Ipomoea batatus (L.) Lam. Eggplant, Solanum melongena L., and tobacco, Nicotiana tabacum L., were common hosts for both biotypes. The cassava-strain whiteflies but not the sweetpotato-reared whiteflies successfully transmitted cassava mosaic virus from disease-infected cassava seedlings to healthy cassava seedlings. Presence of biotypes in B. tabaci is reported for the first time from India.