Tabaci MEAM1 Research Articles

Biochemical, Serological, Molecular and Natural Host Studies on Tomato Chlorosis Virus in Egypt.

Tomato Chlorosis Virus (ToCV) is a white fly-transmitted and phloem-limited crinivirus reported in this study for the first time in Egypt. ToCV caused drastic reduction in tomato yield since 2013. The aim of this study is to characterize the virus incidence using biological, serological and molecular tools. The B. tabaci MEAM1 white fly was used for virus isolation and propagation. Identity of ToCV , its natural hosts were confirmed with RT-PCR using a specific primer pair for ToCV-heat shock protein 70 homologue (HSP70h) gene, sequencing and phylogenetic studies. ToCV was purified using the innovative electro-elution technique. The induced antiserum for the Egyptian isolate of the virus (ToCV-Giza) was used for DAS-ELISA and dot blotting immuno-assays to evaluate the virus presence in tomato and other natural hosts. The ToCV-Giza isolate was donated an accession number "MH667315.1" from the GenBank. Blastx sequence analysis of the HSP70h gene indicated 97-99% of amino acid similarities with many tested ToCV isolates. Phylogenetic studies showed the clustering of all ToCV isolates including ToCV-Giza in a separate group from the other tested criniviruses. The virus had a UV spectrum of a nucleoprotein with Amax and Amin at 260 and 240 nm, respectively and A260/280 ratio of 1.33. Out of 52 different tested plant species within 22 families, 44 were positive hosts for ToCV. Thirty seven out of these 44 plant species were considered as new hosts for ToCV in the present study. These included Ammi majus and Coriandrum sativum (Apiaceae), cabbage (Brassicaceae), sweet potato (Convolvulaceae), melon, cucumber, luffa (Cucurbitaceae), soybean, cowpea, faba bean (Fabaceae), Egyptian and American Cotton (Malvaceae). Several ornamentals either herbal type or woody trees belonging to Acanthaceae, Amaranthaceae, Euophorbiaceae, Moraceae and Rubiaceae were also recognized for the first time as hosts for ToCV. The obtained results confirmed the wide distribution of ToCV in its natural hosts in Egypt. Hygienic measures including control of the virus vector and removing of natural hosts should be strictly implicated.

A Novel Strain of Pepper Leafroll Virus Infecting Common Bean and Soybean in Ecuador

Symptoms resembling those caused by begomoviruses (Geminiviridae: Begomovirus) have been observed in common bean and other leguminous crops in Ecuador in the last few years. The only begomovirus species found infecting legumes (common bean and cowpea) in the country to date is cabbage leaf curl virus (CabLCV) (Fiallo-Olive et al. 2018). During May to June 2017, a survey of leguminous plants was conducted in the Ecuadorian localities of Santa Elena (Santa Elena province), Milagro (Guayas province), and Pallatanga (Chimborazo province). Twenty-four plants showing leaf deformation and/or mosaic symptoms were sampled, including common bean (Phaseolus vulgaris, n = 21), soybean (Glycine max, n = 2), and pigeon pea (Cajanus cajan, n = 1). Most common bean plants were infested with whiteflies (Hemiptera: Aleyrodidae) that were also collected. Total DNA was extracted from leaf samples and used as template in polymerase chain reaction (PCR) using specific primers for CabLCV (MA2540 [5′-GATGTTGAAGCATCTGCAAACATTC-3′] and MA2541 [5′-CTAGGAACATCAGGGCTTCTCAAC-3′]) (Fiallo-Olive et al. 2018). All samples were negative for the presence of CabLCV. DNA extracts were then used as templates in rolling-circle amplification (RCA) using φ29 DNA polymerase (TempliPhi kit, GE Healthcare). Digestion of RCA products with a set of restriction enzymes yielded identical restriction patterns for six samples (five common bean and one soybean), suggesting the presence of a bipartite begomovirus. BamHI and NcoI fragments of approximately 2.6 kbp from a common bean plant were cloned in pBluescript II SK(+), and two selected clones were sequenced (Macrogen, Seoul, South Korea). BLAST analysis showed that the clones corresponded to begomoviral DNA-A (BamHI, 2,580 nt, GenBank accession no. MH481901) and DNA-B (NcoI, 2,561 nt, MH481902). Pairwise identity scores with isolates selected after BLAST analysis were calculated with SDT (Muhire et al. 2014). Cloned DNA-A and DNA-B showed the highest identity (93 and 92%, respectively) with pepper leafroll virus (PepLRV) (KC769819 and KC769820), a bipartite begomovirus identified infecting pepper, common bean, and tomato in Peru (Martinez-Ayala et al. 2014). To confirm the identity of the begomovirus present in the rest of the samples, PCR was performed with specific primers whose design was based on the cloned PepLRV DNA-A (MA2602 [5′-GTTAATGGACAATGAGGGTATGTG-3′] and MA2603 [5′-CACGAGGAGAATAATTGGCGTTAC-3′]) using Taq DNA polymerase (BIOTAQ, Bioline) and thermocycler conditions consisting of 35 cycles with 45 s annealing steps at 57°C. DNA fragments of the expected size (452 bp) were amplified from the six samples, and direct sequencing showed them to be identical to the cloned PepLRV DNA-A, supporting the presence of this virus. Based on the species/strain demarcation threshold for the viruses in the genus Begomovirus (Brown et al. 2015), the isolate characterized here belongs to a new strain of PepLRV. DNA was extracted from individual whiteflies (n = 42) using a Chelex-based method, and PCR was carried out using mitochondrial cytochrome oxidase I gene primers, C1-J-2195 (5′-TTGATTTTTTGGTCATCCAGAAGT-3′) and Btab-uni-PrimerR (5′-CTTAAATTTACTGCACTTTCTGCCAYATTAG-3′). Direct sequencing of PCR products showed that seven sequences (one deposited in GenBank with accession no. MH481903) were identical to numerous sequences of Bemisia tabaci Middle East-Asia Minor 1 (MEAM1, formerly B biotype), known to be an efficient vector of begomoviruses. To our knowledge, this is the first report of PepLRV in Ecuador and of soybean as a host for the virus, which had been identified only in Peru to date. Also, this is the first molecular evidence of the presence of B. tabaci MEAM1 in the country.

Identification of genetic sources with attenuated Tomato chlorosis virus-induced symptoms in Solanum (section Lycopersicon) germplasm

The whitefly-transmitted Tomato chlorosis virus (ToCV) (genus Crinivirus) is associated with yield and quality losses in field and greenhouse-grown tomatoes (Solanum lycopersicum) in South America. Therefore, the search for sources of ToCV resistance/tolerance is a major breeding priority for this region. A germplasm of 33 Solanum (Lycopersicon) accessions (comprising cultivated and wild species) was evaluated for ToCV reaction in multi-year assays conducted under natural and experimental whitefly vector exposure in Uruguay and Brazil. Reaction to ToCV was assessed employing a symptom severity scale and systemic virus infection was evaluated via RT-PCR and/or molecular hybridization assays. A subgroup of accessions was also evaluated for whitefly reaction in two free-choice bioassays carried out in Uruguay (with Trialeurodes vaporariorum) and Brazil (with Bemisia tabaci Middle-East-Asia-Minor1—MEAM1 = biotype B). The most stable sources of ToCV tolerance were identified in Solanum habrochaites PI 127827 (mild symptoms and low viral titers) and S. lycopersicum ‘LT05’ (mild symptoms but with high viral titers). These two accessions were efficiently colonized by both whitefly species, thus excluding the potential involvement of vector-resistance mechanisms. Other promising breeding sources were Solanum peruvianum (sensu lato) ‘CGO 6711’ (mild symptoms and low virus titers), Solanum chilense LA1967 (mild symptoms, but with high levels of B. tabaci MEAM1 oviposition) and Solanum pennellii LA0716 (intermediate symptoms and low level of B. tabaci MEAM1 oviposition). Additional studies are necessary to elucidate the genetic basis of the tolerance/resistance identified in this set of Solanum (Lycopersicon) accessions.

Performance of Bemisia tabaci MEAM1 and Trialeurodes vaporariorum on Tomato chlorosis virus (ToCV) infected plants

AbstractWhiteflies are important agricultural pests of several crops and cause great economic losses, mainly by the transmission of plant viruses. Among the different species of whiteflies, Trialeurodes vaporariorum and Bemisia tabaci MEAM1 (B biotype) transmit the crinivirus Tomato chlorosis virus (ToCV). Previous studies report that virus‐infected plants can influence the attractiveness and the behaviour of different species of whiteflies. In this study, we evaluated the number of eggs, egg hatching rate and emergence of adults of both T. vaporariorum and B. tabaci MEAM1 on ToCV‐infected and healthy tomatoes. In addition, ToCV transmission assays were conducted with both whitefly species. ToCV infection did not influence the number of eggs or egg hatching rate of T. vaporariorum; whereas the emergence of adults was reduced by 37.3% on ToCV‐infected tomatoes. By contrast, ToCV‐infected tomatoes strongly affected the B. tabaci MEAM1 egg hatching rate and emergence of adults with reductions of 41.8% and 92.4%, respectively. Regarding virus transmission, T. vaporariorum transmitted ToCV with lower efficiency (35.7%) than B. tabaci MEAM1 (78.6%). Our data suggest that the performance of T. vaporariorum is less affected than that of B. tabaci MEAM1 when feeding on ToCV‐infected tomato plants.

Genome-wide analysis of odorant-binding proteins and chemosensory proteins in the sweet potato whitefly, Bemisia tabaci.

Odorant‐binding proteins (OBPs) and chemosensory proteins (CSPs) of insects are thought to play roles in olfactory recognition affecting host choice, copulation, reproduction and other behaviors. Previous descriptions of OBPs and CSPs in the whitefly Bemisia tabaci often provided no or incomplete genetic information. In this study, we present a genome‐wide and transcriptome‐wide investigation of the OBPs and CSPs in B. tabaci MEAM1 (Middle East‐Asia Minor1 species). Eight OBP and 19 CSP genes were identified that covered all previous sequences. Phylogenetic analyses showed that the CSP genes had a lineage‐specific expansion (BtabBCSP1, BtabBCSP3, BtabBCSP13, BtabBCSP17, BtabBCSP18 and BtabBCSP19). Expression profiling of OBPs and CSPs by transcriptome sequencing and quantitative real‐time polymerase chain reaction (qPCR) revealed that expression patterns differed among developmental stages of B. tabaci MEAM1. Five OBP genes and 11 CSP genes significantly differed between males and females; four of the 19 CSP genes were highly expressed in adults, while two were highly expressed in nymphs. The expression profiles of the OBP and CSP genes in different tissues of B. tabaci MEAM1 adults were analyzed by qPCR. Four OBP genes found in B. tabaci MEAM1 were highly expressed in the head. Conversely, only two CSPs were enriched in the head, while the other six CSPs were specifically expressed in other tissues. Our results provide a foundation for future research on OBPs and CSPs in B. tabaci.

The level of midgut penetration of two begomoviruses affects their acquisition and transmission by two species of Bemisia tabaci

Begomoviruses are transmitted by whiteflies in a persistent manner, but factors responsible for the variation of virus transmission by different species are poorly understood. We examined ingestion of papaya leaf curl China virus (PaLCuCNV) and tomato yellow leaf curl virus (TYLCV) by two species of the Bemisia tabaci complex, MEAM1 and MED, and then quantified the virion concentrations in different organs/tissues in each species. We found that PaLCuCNV penetrated the midgut wall of MED less efficiently than MEAM1, resulting in lower efficiency of PalCuCNV transmission by MED than that by MEAM1, while TYLCV penetrated the midgut wall of both species and was transmitted by them at similar levels of efficiency. Virus coat protein determined the virus capacity to cross the midgut wall of a given whitefly species. These data indicate that the level of midgut penetration determines virus acquisition and transmission by whiteflies in the first instance.

Numerical host plant relationships of Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) within and among major Australian field crops

AbstractThe within‐plant, vertical (internodal) distribution of the silverleaf whitefly (SLW), Bemisia tabaci (Gennadius) MEAM1 (biotype B) adult, large nymph (3rd and 4th instar) and egg stages was quantified in relation to four major Australian field crops, viz., cotton, mungbean, soybean and sunflower in 2003. The objective was to identify suitable sampling locations within the crop canopy. Ovipositional preference of SLW among the four crops under field conditions was also determined to gauge potential susceptibility and support crop choice and configuration decisions in multi‐crop systems. SLW abundance at main stem leaf nodes within each crop was characterised in a two‐stage analysis of the proportion of infested nodes and the number of SLW at the node if infested. The vertical distribution profiles of adults and nymphs from the experimental plots were validated for cotton using scouting data collected in the 2002–2003 growing season and for mungbean from an agronomic comparison of commercial germplasm conducted in 2003. Vertical distributions of adults and juvenile stages differed among the four crops. Based on their distribution profiles, the optimal sampling locations in cotton, mungbean, soybean and sunflower are leaf nodes 3–5, 2–3, 3–4 and 5–7 for adult SLW and 7–10, 4–5, 5–6 and 17–21 for large nymphs, respectively. A comparison of egg density per unit area of green leaf among the four host plant species indicated that soybean is the most attractive to ovipositing females, mungbean the least, and cotton and sunflower intermediate. The potential of each crop as a source for SLW on the basis of nymph abundance is discussed. Low preference combined with a low source potential makes mungbean the crop of choice in broad acre cropping areas in which SLW is endemic.

Features of the relationship between Tomato severe rugose begomovirus and Bemisa tabaci MEAM1 reveal that the virus is acquired during a probe lasting only one minute

Tomato severe rugose virus (ToSRV) is a begomovirus found only in Brazil and has been the prevalent species affecting tomato crops in southwest and midwest of the country. Although the virus is known to be transmitted by Bemisia tabaci MEAM1, this study was undertaken to better characterize the relationship between ToSRV and whiteflies on tomato plants. The minimum acquisition and inoculation access periods, latent period, and virus retention time in the vector were determined. The results of transmission experiments showed that the minimum acquisition and inoculation access periods (AAP and IAP) for transmission of ToSRV by MEAM1 were 1 min and 5 min, respectively. After monitoring 50 individual adult whiteflies during a one-minute AAP on ToSRV-infected tomato leaves, 21 insects (42%) were able to acquire the virus, as confirmed by PCR. In contrast, one hundred insects that were individually allowed one-minute AAP on Tomato chlorosis virus (ToCV)-infected tomato leaves, which is a phloem-limited crinivirus, were unable to acquire the virus. The latent period of ToSRV in MEAM1 was 12–15 h, with adult whiteflies retaining the virus for 25 days. Although the tissue distribution of ToSRV in tomato has not been determined, the short AAP suggests that the virus may be present in mesophyll cells, from where it may be acquired during a one-minute feeding probe.

Plant-mediated horizontal transmission of Rickettsia endosymbiont between different whitefly species.

A growing number of studies have revealed the presence of closely related endosymbionts in phylogenetically distant arthropods, indicating horizontal transmission of these bacteria. Here we investigated the interspecific horizontal transmission of Rickettsia between two globally invasive whitefly species, Bemisia tabaci MEAM1 and B. tabaci MED, via cotton plants. We found both scattered and confined distribution patterns of Rickettsia in these whiteflies. After entering cotton leaves, Rickettsia was restricted to the leaf phloem vessels and could be taken up by both species of the Rickettsia-free whitefly adults, but only the scattered pattern was observed in the recipient whiteflies. Both the relative quantity of Rickettsia and the efficiency of transmitting Rickettsia into cotton leaves were significantly higher in MEAM1 females than in MED females. The retention time of Rickettsia transmitted from MEAM1 into cotton leaves was at least 5 days longer than that of MED. Phylogenetic analysis based on 16S rRNA and gltA genes confirmed that the Rickettsia extracted from the donor MEAM1, the cotton leaves, the recipient MEAM1 and the recipient MED were all identical. We conclude that cotton plants can mediate horizontal transmission of Rickettsia between different insect species, and that the transmission dynamics of Rickettsia vary with different host whitefly species.

Comparative transcriptome analysis reveals networks of genes activated in the whitefly, Bemisia tabaci when fed on tomato plants infected with Tomato yellow leaf curl virus

The whitefly Bemisia tabaci can transmit hundreds of viruses to numerous agricultural crops in the world. Five genera of viruses, including Begomovirus and Crinivirus, are transmitted by B. tabaci. There is little knowledge about the genes involved in virus acquisition and transmission by whiteflies. Using a comparative transcriptomics approach, we evaluated the gene expression profiles of whiteflies (B. tabaci MEAM1) after feeding on tomato infected by a begomovirus, Tomato yellow leaf curl virus (TYLCV), in comparison to a recent study, in which whiteflies were fed on tomato infected by the crinivirus, Tomato chlorosis virus (ToCV). The data revealed similar temporal trends in gene expression, but large differences in the number of whitefly genes when fed on TYLCV or ToCV-infected tomato. Transcription factors, cathepsins, receptors, and a hemocyanin gene, which is implicated in mediating antiviral immune responses in other insects and possibly virus transmission, were some of the genes identified.

Genome-Wide Characterization and Expression Profiling of Sugar Transporter Family in the Whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae).

Sugar transporters (STs) play pivotal roles in the growth, development, and stress responses of phloem-sucking insects, such as the whitefly, Bemisia tabaci. In this study, 137 sugar transporters (STs) were identified based on analysis of the genome and transcriptome of B. tabaci MEAM1. B. tabaci MEAM1 encodes a larger number of STs than other selected insects. Phylogenetic and molecular evolution analysis showed that the 137 STs formed three expanded clades and that the genes in Sternorrhyncha expanded clades had accelerated rates of evolution. B. tabaci sugar transporters (BTSTs) were divided into three groups based on their expression profiles across developmental stages; however, no host-specific BTST was found in B. tabaci fed on different host plants. Feeding of B. tabaci adults with feeding diet containing dsRNA significantly reduced the transcript level of the target genes in B. tabaci and mortality was significantly improved in B. tabaci fed on dsRNA compared to the control, which indicates the sugar transporters may be used as potential RNAi targets for B. tabaci bio-control. These results provide a foundation for further studies of STs in B. tabaci.

Single-Target and Multiplex Discrimination of Whiteflies (Hemiptera: Aleyrodidae) Bemisia tabaci and Trialeurodes vaporariorum With Modified Priming Oligonucleotide Thermodynamics.

The whitefly species Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood) are worldwide agricultural pests and virus vectors. Bemisia tabaci, in particular, is often transported internationally via trade routes leading to potential introductions of exotic whiteflies or plant viruses. Quick identification of agriculturally important whiteflies can facilitate interventions that prevent these cross-border introductions. Polymerase chain reaction (PCR) primers were designed to amplify the mitochondrial cytochrome oxidase I gene (mtCOI) sequence of members of the B. tabaci complex, MEAM1, MED, and NW, and T. vaporariorum. Primers incorporated an A/T-rich overhang sequence at the 5' terminus (5' flap) to test for increased primer sensitivity and assay efficiency. Single-target and multiplex endpoint PCR assays with the eight primer sets were performed using genomic DNA template extracted from individual adult whiteflies. Resultant PCR amplicons obtained for B. tabaci MEAM1, MED, and NW, and T. vaporariorum primers with the 5' flap were 559-, 717-, 353-, and 258-bp, respectively, and without the 5' flap were 550-, 712-, 329-, and 252-bp in length, respectively. In single-target and multiplex reactions, specific amplification was achieved using both the unmodified and 5' flap-modified primers. Sequencing and phylogenetic analysis confirmed primer-target amplification specificity. Using these primer sets in single-target or multiplex PCR allows for quick discrimination and specific identification of B. tabaci complex members and T. vaporariorum, and the addition of 5'A/T-rich overhang sequences increases the sensitivity and amplification of some primer sets.

Transcriptome analysis of the whitefly, Bemisia tabaci MEAM1 during feeding on tomato infected with the crinivirus, Tomato chlorosis virus, identifies a temporal shift in gene expression and differential regulation of novel orphan genes

BackgroundWhiteflies threaten agricultural crop production worldwide, are polyphagous in nature, and transmit hundreds of plant viruses. Little is known how whitefly gene expression is altered due to feeding on plants infected with a semipersistently transmitted virus. Tomato chlorosis virus (ToCV; genus Crinivirus, family Closteroviridae) is transmitted by the whitefly (Bemisia tabaci) in a semipersistent manner and infects several globally important agricultural and ornamental crops, including tomato.ResultsTo determine changes in global gene regulation in whiteflies after feeding on tomato plants infected with a crinivirus (ToCV), comparative transcriptomic analysis was performed using RNA-Seq on whitefly (Bemisia tabaci MEAM1) populations after 24, 48, and 72 h acquisition access periods on either ToCV-infected or uninfected tomatoes. Significant differences in gene expression were detected between whiteflies fed on ToCV-infected tomato and those fed on uninfected tomato among the three feeding time periods: 447 up-regulated and 542 down-regulated at 24 h, 4 up-regulated and 7 down-regulated at 48 h, and 50 up-regulated and 160 down-regulated at 72 h. Analysis revealed differential regulation of genes associated with metabolic pathways, signal transduction, transport and catabolism, receptors, glucose transporters, α-glucosidases, and the uric acid pathway in whiteflies fed on ToCV-infected tomatoes, as well as an abundance of differentially regulated novel orphan genes. Results demonstrate for the first time, a specific and temporally regulated response by the whitefly to feeding on a host plant infected with a semipersistently transmitted virus, and advance the understanding of the whitefly vector-virus interactions that facilitate virus transmission.ConclusionWhitefly transmission of semipersistent viruses is believed to require specific interactions between the virus and its vector that allow binding of virus particles to factors within whitefly mouthparts. Results provide a broader understanding of the potential mechanism of crinivirus transmission by whitefly, aid in discerning genes or loci in whitefly that influence virus interactions or transmission, and subsequently facilitate development of novel, genetics-based control methods against whitefly and whitefly-transmitted viruses.

RNA interference of an antimicrobial peptide, Btdef, reduces Tomato yellow leaf curl China virus accumulation in the whitefly Bemisia tabaci.

The whitefly Bemisia tabaci (Gennadius) is considered one of the main pests for agriculture. One important problem with the whitefly is its notorious status as a vector for plant viruses, primarily begomoviruses. We have previously identified a defensin-like antimicrobial peptide, Btdef, from the whitefly B. tabaci MEAM1. However, the function of Btdef in the immune system of the insect vector and begomovirus transmission has yet to be explored. To explore the role of Btdef during begomovirus transmission, we firstly investigated the transcriptional response of Btdef following acquisition of Tomato yellow leaf curl China virus (TYLCCNV). The expression of Btdef was up-regulated in the viruliferous whiteflies. After RNA silencing of the Btdef gene in adult whiteflies fed with dsRNA, they were allowed to feed on TYLCCNV-infected plants and then quantified for TYLCCNV DNA titre. Unexpectedly, silencing the Btdef gene reduced both the abundance and expressions of TYLCCNV genes in the whiteflies. In the meantime, the density of the endosymbiont Rickettsia was significantly reduced in dsBtdef-fed whiteflies. Our data provide evidence that Btdef is involved in begomovirus infection, possibly through symbiont-mediated alteration of begomovirus-whitefly interactions. These findings indicate that Btdef may be targeted for the development of new technology for the control of whitefly-transmitted begomoviruses. © 2016 Society of Chemical Industry.

Presence of Native Prey Does Not Divert Predation on Exotic Pests by Harmonia axyridis in Its Indigenous Range.

In China, two invasive pests, Bemisia tabaci MEAM1 (Gennadius) and Frankliniella occidentalis (Pergande), often co-occur with the native pest, Aphis gossypii (Glover), on plants of Malvaceae and Cucurbitaceae. All three are preyed on by the native ladybird, Harmonia axyridis (Pallas); however, the native predator might be expected to prefer native prey to the exotic ones due to a shared evolutionary past. In order to clarify whether the presence of native prey affected the consumption of these two invasive species by the native predator, field-cage experiments were conducted. A duplex qPCR was used to simultaneously detect both non-native pests within the gut of the predator. H. axyridis readily accepted both invasive prey species, but preferred B. tabaci. With all three prey species available, H. axyridis consumption of B. tabaci was 39.3±2.2% greater than consumption of F. occidentalis. The presence of A. gossypii reduced (by 59.9% on B. tabaci, and by 60.6% on F. occidentalis), but did not stop predation on the two exotic prey when all three were present. The consumption of B. tabaci was similar whether it was alone or together with A. gossypii. However, the presence of aphids reduced predation on the invasive thrips. Thus, some invasive prey may be incorporated into the prey range of a native generalist predator even in the presence of preferred native prey.

Leaf Morphological Characters Can Be a Factor for Intra-Varietal Preference of Whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) among Eggplant Varieties.

The sweetpotato whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae) MEAM1, is considered a serious pest of horticultural and many other crops. While eggplant (Solanum melongena) is one of the most favored host plants, the whiteflies exhibit preferences among different varieties. We hypothesized that certain morphological leaf characteristics of different varieties, like leaf trichome density, trichome length, leaf lamina thickness and leaf color, may affect whitefly landing, feeding and oviposition. In this study, we investigated the variation in leaf morphological characters among selected eggplant varieties and evaluated the effect of these leaf characteristics in rendering eggplant varieties either susceptible or resistant to B. tabaci. We evaluated eight eggplant varieties in choice feeding tests, and we found that the varieties JinSheng Zilongchangqie (JSZ) and H149 were the highly preferred varieties with the highest numbers of whitefly adults and eggs. Significantly lower numbers of whitefly adult eggs were found on the resistant variety Tuo Lu Bamu (TLB). The varieties JinGuangbo Luqie (JGL), JinGuangbo Ziquanqie (JGZ), DaYang Ziguanqie (DYZ), QinXing Ziguanqie (QXZ), and QinXing Niuxinqie (QXN) were moderately favored by B. tabaci. Leaf trichome density, trichome length and leaf lamina thickness were positively correlated with numbers of whitefly adults and eggs. B. tabaci was less attracted to the leaves that reflect long and middle wavelength light (higher R and G values) than to the bright green leaves (medium G value), but the short wavelength light (higher B value) had no significant effect on whitefly preference. The degree of hue had a positive effect, and saturation and brightness had a negative effect on whitefly attraction.

Evolutionary conservation of candidate osmoregulation genes in plant phloem sap‐feeding insects

The high osmotic pressure generated by sugars in plant phloem sap is reduced in phloem-feeding aphids by sugar transformations and facilitated water flux in the gut. The genes mediating these osmoregulatory functions have been identified and validated empirically in the pea aphid Acyrthosiphon pisum: sucrase 1 (SUC1), a sucrase in glycoside hydrolase family 13 (GH13), and aquaporin 1 (AQP1), a member of the Drosophila integral protein (DRIP) family of aquaporins. Here, we describe molecular analysis of GH13 and AQP genes in phloem-feeding representatives of the four phloem-feeding groups: aphids (Myzus persicae), coccids (Planococcus citri), psyllids (Diaphorina citri, Bactericera cockerelli) and whiteflies (Bemisia tabaci MEAM1 and MED). A single candidate GH13-SUC gene and DRIP-AQP gene were identified in the genome/transcriptome of most insects tested by the criteria of sequence motif and gene expression in the gut. Exceptionally, the psyllid Ba. cockerelli transcriptome included a gut-expressed Pyrocoelia rufa integral protein (PRIP)-AQP, but has no DRIP-AQP transcripts, suggesting that PRIP-AQP is recruited for osmoregulatory function in this insect. This study indicates that phylogenetically related SUC and AQP genes may generally mediate osmoregulatory functions in these diverse phloem-feeding insects, and provides candidate genes for empirical validation and development as targets for osmotic disruption of pest species.

Lethal and sublethal effects of a novel cis-nitromethylene neonicotinoid insecticide, cycloxaprid, on Bemisia tabaci

The tobacco whitefly, Bemisia tabaci (Gennadius), is an important pest because of its potential to threaten agricultural crops worldwide. Currently, this pest is controlled by the application of chemical insecticides. In our pursuit to identify better insecticides for an effective control of this insect pest, we investigated the lethal effects of five neonicotinoid insecticides including four commercial neonicotinoids and a novel neonicotinoid (cycloxaprid) on B. tabaci MED and MEAM1 cryptic species. In addition, we assessed the sublethal effects of cycloxaprid on B. tabaci MED. Lethal effects of the insecticides were determined using the leaf-dip bioassay, and the results showed that among the tested insecticides cycloxaprid was more toxic to B. tabaci MED and MEAM1 than others, with LC50 values of 0.70 mg/L and 0.59 mg/L, respectively. Cycloxaprid at LC25 (0.16 mg/L) induced sublethal effects in adult MED by prolonging the developmental periods and decreasing the survival rates of all larval instars, pseudopupal and adult stages. Moreover, it significantly shortened the oviposition period of females and decreased their fecundity. Hatching rate of eggs laid by females exposed to LC25 was also markedly reduced. These results indicate that cycloxaprid is a novel alternate insecticide that may effectively control B. tabaci populations.

MicroRNA profiling of the whitefly Bemisia tabaci Middle East-Aisa Minor I following the acquisition of Tomato yellow leaf curl China virus.

BackgroundThe begomoviruses are the largest and most economically important group of plant viruses exclusively vectored by whitefly (Bemisia tabaci) in a circulative, persistent manner. During this process, begomoviruses and whitefly vectors have developed close relationships and complex interactions. However, the molecular mechanisms underlying these interactions remain largely unknown, and the microRNA profiles for viruliferous and nonviruliferous whiteflies have not been studied.MethodsSequences of Argonaute 1(Ago1) and Dicer 1 (Dcr1) genes were cloned from B. tabaci MEAM1 cDNAs. Subsequently, deep sequencing of small RNA libraries from uninfected and Tomato yellow leaf curl China virus (TYLCCNV)-infected whiteflies was performed. The conserved and novel miRNAs were identified using the release of miRBase Version 19.0 and the prediction software miRDeep2, respectively. The sequencing results of selected deregulated and novel miRNAs were further confirmed using quantitative reverse transcription-PCR. Moreover, the previously published B. tabaci MEAM1 transcriptome database and the miRNA target prediction algorithm miRanda 3.1 were utilized to predict potential targets for miRNAs. Gene Ontology (GO) analysis was also used to classify the potential enriched functional groups of their putative targets.ResultsAgo1 and Dcr1orthologs with conserved domains were identified from B. tabaci MEAM1. BLASTn searches and sequence analysis identified 112 and 136 conserved miRNAs from nonviruliferous and viruliferous whitefly libraries respectively, and a comparison of the conserved miRNAs of viruliferous and nonviruliferous whiteflies revealed 15 up- and 9 down-regulated conserved miRNAs. 7 novel miRNA candidates with secondary pre-miRNA hairpin structures were also identified. Potential targets of conserved and novel miRNAs were predicted using GO analysis, for the targets of up- and down-regulated miRNAs, eight and nine GO terms were significantly enriched.ConclusionsWe identified Ago1 and Dcr1 orthologs from whiteflies, which indicated that miRNA-mediated silencing is present in whiteflies. Our comparative analysis of miRNAs from TYLCCNV viruliferous and nonviruliferous whiteflies revealed the relevance of deregulated miRNAs for the post-transcriptional gene regulation in these whiteflies. The potential targets of all expressed miRNAs were also predicted. These results will help to acquire a better understanding of the molecular mechanism underlying the complex interactions between begomoviruses and whiteflies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-016-0469-7) contains supplementary material, which is available to authorized users.

Oogenesis in the Bemisia tabaci MEAM1 species complex

The whitefly Bemisia tabaci MEAM1 species complex has invaded several parts of the world in the past 30 years and replaced native whitefly populations in the invaded regions, including certain areas of China. One of the possible reasons for the invasion is that MEAM1 whiteflies are more fecund than native species. However, the factors that affect the reproduction of the B. tabaci cryptic species are not clearly known. The regulation of oogenesis is thought to be one of the essential processes for egg formation and ovary development and could affect its population dynamics. In this study, the ovariole structure and oogenesis of the MEAM1 species complex was examined using light and transmission electron microscopy. Telotrophic ovarioles were observed in the MEAM1 species complex. Each ovariole had two well defined regions: the tropharium and the vitellarium. The tropharium always had more than ten trophocytes. The development of a single oocyte in the vitellarium has four phases: oocyte formation, previtellogenesis, vitellogenesis and choriogenesis. Two arrested oocytes, follicular cells and uncompleted oocytes were separated from the tropharium by microtubule and microfilaments. Early previtellogenesis oocytes absorbed nutrients and endosymbiont bacteria through a nutritive cord. However, the vitellogenesis of oocytes transmitted Vg through both the nutritive cord and the space between follicular cells. Each mature oocyte with deposited yolk proteins had only one bacteriocyte and was surrounded by a single layer of follicular cells. The oogenesis in the B. tabaci MEAM1 species complex concluded with the differentiation of oocytes, the transport of yolk and endosymbionts as well as the development and maturation of oocytes. This result provides important information that further defines the regulation of oogenesis in the B. tabaci complex.