The transmission of geminiviruses byBemisia tabaci

Four Most Pathogenic Superfamilies of Insect Pests of Suborder Sternorrhyncha: Invisible Superplunderers of Plant Vitality

Sternorrhyncha representatives are serious pests of agriculture and forestry all over the world, primarily causing damage to woody plants. Sternorrhyncha members are vectors for the transfer of a large number of viral diseases, and subsequently, the host plant weakens. Additionally, many are inherent in the release of honeydew, on which fungal diseases develop. Today, an innovative approach is needed to create new and effective ways to control the number of these insects based on environmentally friendly insecticides. Of particular relevance to such developments is the need to take into account the large number of organisms living together with insect pests in this group, including beneficial insects. Practically without changing their location on their host plant, they adopted to be more invisible and protected due to their small size, symbiosis with ants, the ability to camouflage with a leaf, and moderately deplete plants and others, rarely leading them to death but still causing substantial economic loss in the subtropics and tropics. Due to the lack of presence in the literature, this review fills in this pesky spot by examining (on the example of distinct species from four superfamilies) the characteristic adaptations for this suborder and the chemical methods of combating these insects that allow them to survive in various environmental conditions, suggesting new and highly promising ways of using olinscides for plant protection against Sternorrhyncha members.

Earlier than expected introductions of the Bemisia tabaci B mitotype in Brazil reveal an unprecedented, rapid invasion history

During 1991, in Brazil, the presence of the exotic Bemisia tabaci B mitotype was reported in São Paulo state. However, the duration from the time of initial introduction to population upsurges is not known. To investigate whether the 1991 B mitotype outbreaks in Brazil originated in São Paulo or from migrating populations from neighboring introduction sites, country-wide field samples of B. tabaci archived from 1989-2005 collections were subjected to analysis of mitochondrial cytochrome oxidase I (mtCOI) and nuclear RNA-binding protein 15 (RP-15) sequences. The results of mtCOI sequence analysis identified all B. tabaci as the NAFME 8 haplotype of the B mitotype. Phylogenetic analyses of RP-15 sequences revealed that the B mitotype was likely a hybrid between a B type parent related to a haplotype Ethiopian endemism (NAFME 1-3), and an unidentified parent from the North Africa-Middle East (NAF-ME) region. Results provide the first evidence that this widely invasive B mitotype has evolved from a previously undocumented hybridization event. Samples from Rio de Janeiro (1989) and Ceará state (1990), respectively, are the earliest known B mitotype records in Brazil. A simulated migration for the 1989 introduction predicted a dispersal rate of 200-500 km/year, indicating that the population was unlikely to have reached Ceará by 1990. Results implicated two independent introductions of the B mitotype in Brazil in 1989 and 1990, that together were predicted to have contributed to the complete invasion of Brazil in only 30 generations.

Controlling Geminiviruses before Transmission: Prospects

Whitefly (Bemisia tabaci)-transmitted Geminiviruses cause serious diseases of crop plants in tropical and sub-tropical regions. Plants, animals, and their microbial symbionts have evolved complex ways to interact with each other that impact their life cycles. Blocking virus transmission by altering the biology of vector species, such as the whitefly, can be a potential approach to manage these devastating diseases. Virus transmission by insect vectors to plant hosts often involves bacterial endosymbionts. Molecular chaperonins of bacterial endosymbionts bind with virus particles and have a key role in the transmission of Geminiviruses. Hence, devising new approaches to obstruct virus transmission by manipulating bacterial endosymbionts before infection opens new avenues for viral disease control. The exploitation of bacterial endosymbiont within the insect vector would disrupt interactions among viruses, insects, and their bacterial endosymbionts. The study of this cooperating web could potentially decrease virus transmission and possibly represent an effective solution to control viral diseases in crop plants.

Complete genome sequence of a new bipartite begomovirus associated with leaf curl disease of Capsicum annum

The complete bipartite genome, consisting of DNA-A and DNA-B, of a novel begomovirus isolate associated with apical leaf curling and crinkled leaf disease of Chili (Capsicum annum) from New Delhi, India was cloned and sequenced. The sequence of DNA-A (2737 nt) and DNA-B (2692 nt) of the virus was submitted to NCBI, USA under the accessions MK069591 & MG597211, respectively. Sequence identity of the common region (CR) and presence of identical iterons (GAGTG) between the DNA-A and DNA-B clones indicate that they constitute a related pair. The virus corresponds to a novel species of tomato leaf curl virus and sequence analysis has ruled out the involvement of recombination events in its evolution. Therefore, we report the complete nucleotide sequence of a new bipartite begomovirus infecting Capsicum annum, a vegetable crop communally cultivated throughout India.

Mapping global risk levels of Bemisia tabaci in areas of suitability for open field tomato cultivation under current and future climates

The whitefly, Bemisia tabaci, is a major threat to tomato Solanum lycopersicum and ranks as one of the world's 100 most invasive pests. This is the first study of B. tabaci (Biotype B and Q) global distribution, focusing on risk levels of this invasive pest, in areas projected to be suitable for open field S. lycopersicum cultivation under climate change. This study aims to identify levels of risk of invasive B. tabaci for areas of suitability for open field S. lycopersicum cultivation for the present, 2050 and 2070 using MaxEnt and the Global Climate Model, HadGEM2_ES under RCP45. Our results show that 5% of areas optimal for open field S. lycopersicum cultivation are currently at high risk of B. tabaci. Among the optimal areas for S. lycopersicum, the projections for 2050 compared to the current time showed an extension of 180% in areas under high risk, and a shortening of 67 and 27% in areas under medium and low risk of B. tabaci, respectively, while projections for 2070 showed an extension of 164, and a shortening of 49 and 64% under high, medium and low risk, respectively. The basis of these projections is that predicted temperature increases could affect the pest, which has great adaptability to different climate conditions, but could also impose limitations on the growth of S. lycopersicum. These results may be used in designing strategies to prevent the introduction and establishment of B. tabaci for open-field tomato crops, and assist the implementation of pest management programs.

Foraging behaviour of the parasitoid Eretmocerus eremicus under intraguild predation risk by Macrolophus pygmaeus

BACKGROUND

Intraguild predation (IGP), predation between species that use a common resource, can affect the populations of a pest, of the pest's natural enemy (IG prey) and of the predator of the pest's natural enemy (IG predator). In this study, we determined whether the parasitoid Eretmocerus eremicus (Hymenoptera: Aphelinidae) (IG prey), modifies its foraging behaviour under the risk of IGP by Macrolophus pygmaeus (Hemiptera: Miridae) (IG predator). Parasitoid behaviour was analysed using two bioassays (choice and no-choice) with the following treatments: (i) control, tomato leaf infested with whitefly nymphs; and (ii) PEP, tomato leaf infested with whitefly nymphs and previously exposed to the IG predator; and (iii) PP, tomato leaf infested with whitefly nymphs, with both, the IG predator and the IG prey present.

RESULTS

In both bioassays, we found that E. eremicus did not significantly modify the number of ovipositions, time of residence, duration of oviposition or behavioural sequence. However, in the no-choice bioassay, the number of attacks was higher and their duration shorter in the PEP treatment than in the control.

CONCLUSION

Our results indicate that the parasitoid may detect IGP risk to a certain extent, but it did not significantly modify its foraging behaviour, suggesting that simultaneous release of the two natural enemies can be successfully employed.

Dissipation rate of thiacloprid and its control effect against Bemisia tabaci in greenhouse tomato after soil application

BACKGROUND

Thiacloprid is a chloronicotinyl insecticide that is quite effective against sucking insects. In this study, when thiacloprid was applied at two different rates (normal rate 15 kg ha(-1) , double rate 30 kg ha(-1) ), the systemic distribution and residue of thiacloprid as well as its control effect against whitefly (Bemisia tabaci) were investigated in greenhouse tomato after soil application.

RESULTS

The results showed that thiacloprid was present in the tomato leaves until day 25, and then its amount was less than 0.005 mg kg(-1) and could not be detected. Thiacloprid residue in the tomato stems basically remained at a stable low level throughout the experimental period. Thiacloprid in soil had half-lives of 11.8 and 12.5 days for the normal treatment and the double treatment respectively. The control efficiency of whiteflies was about 90% from day 1 to day 10. This was followed by a slow decline, but efficiency was still higher than 50% until day 21. In addition, no significant differences were noted in the control effect of thiacloprid on whiteflies between the two different rates.

CONCLUSION

Soil application of thiacloprid at the normal rate can effectively control whiteflies, with high efficiency and long persistence.

Biotype status and genetic polymorphism of the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) in Greece: mitochondrial DNA and microsatellites

The genetic polymorphism and the biotype identity of the tobacco whitefly Bemisia tabaci (Gennadius) have been studied in population samples taken from different localities within Greece from cultivated plants growing in greenhouses or in open environments and from non-cultivated plants. Two different approaches were used: sequencing of the mitochondrial cytochrome oxidase I (mtCOI) gene and genotyping using microsatellite markers. Analyses of the mtCOI sequences revealed a high homogeneity between the Greek samples which clustered together with Q biotype samples that had been collected from other countries. When genetic polymorphism was examined using six microsatellite markers, the Greek samples, which were all characterized as Q biotype were significantly differentiated from each other and clustered into at least two distinct genetic populations. Moreover, based on the fixed differences revealed by the mtCOI comparison of known B. tabaci biotype sequences, two diagnostic tests for discriminating between Q and B and non-Q/non-B biotypes were developed. Implementation of these diagnostic tools allowed an absence of the B biotype and presence of the Q biotype in the Greek samples to be determined.

Whitefly transmission of sweet potato viruses

Three genera of plant viruses, Begomovirus (Geminiviridae), Crinivirus (Closteroviridae) and Ipomovirus (Potyviridae), contain members that infect sweet potato (Ipomoea batatas) and are transmitted by whiteflies. The begomoviruses, Sweet potato leaf curl virus (SPLCV) and Ipomoea leaf curl virus (ILCV), and the ipomovirus Sweet potato mild mottle virus are transmitted by Bemisia tabaci, the sweet potato whitefly. The crinivirus, Sweet potato chlorotic stunt virus (SPCSV), is transmitted by B. tabaci and Trialeurodes abutilonea, the bandedwinged whitefly. Transmission experiments were done with three of these viruses using laboratory-reared whiteflies and 2-day acquisition and transmission feeding periods. SPLCV and ILCV were transmitted from single and double infections by B. tabaci at rates of 5-10%. Transmission rates for SPLCV by B. tabaci were 15-20%. T. abutilonea transmitted SPCSV at a rate of ca. 3% but did not transmit ILCV or SPLCV.

DNA Analysis Confirms Macroptilium lathyroides as Alternative Host of Bean golden yellow mosaic virus

The leguminous weed Macroptilium lathyroides is considered a potential host of the Bean golden yellow mosaic virus (BGYMV; BGMV = Mesoamerican isolates). To determine if M. lathyroides could be a host for BGYMV, an infectivity cycle was established between this weed and Phaseolus vulgaris. Virus transmission was carried out using the whitefly, Bemisia argentifolli, as a vector. Inoculated plants of both species were examined for symptoms such as mosaic, stunting, and leaf distortion. P. vulgaris and M. lathyroides showed golden yellow mosaic symptoms during all infectivity cycle stages. Symptomatic plants of both species were tested for BGYMV using polymerase chain reaction (PCR) and nucleotide sequence analysis. Two degenerate primers sets were used for PCR to detect viral DNA: PAL1v1978/PAR1c715 and PCRc2/PBL12039. PCR analysis using primers PCRc2/PBL12039 amplified viral DNA for component B from both plant species. Nucleotide sequence analysis revealed a 93% identity between the virus isolated from M. lathyroides and the Puerto Rican isolate of BGYMV. These results confirmed that M. lathyroides could serve as an alternative host of BGYMV and that an infectivity cycle of BGYMV could possibly occur between P. vulgaris and M. lathyroides in Puerto Rico.

Development of a continuous whitefly cell line [Homoptera: Aleryrodidae: Bemisia tabaci (Gennadius)] for the study of begomovirus

The whitefly Bemisia tabaci (Gennadius) is a widely distributed pest of many important food and fiber crops. This whitefly is also a vector of more than 70 plant-infecting viruses. A cell line was established in vitro using embryonic tissues from the eggs of Bemisia tabaci (Gennadius), B biotype (pseudonym B. argentifolii Bellows & Perring), and referred to as 'Btb(Ba)97, Hunter-Polston'. Cell cultures were successfully inoculated with begomovirus (BGMV and ToMoV)-infected tomato plant sap. Embryonic tissues were seeded into Kimura's modified medium and kept at a temperature of 24 degrees C. Continuous cell cultures were established and have since undergone 92 passages in 25-cm(2) flasks. Cell doubling time is approximately 3 days and the cells have been successfully revived after 1 year after storage at -80 degrees C. The cell population is monolayers of predominately fibroblast with some epithelial cells. Begomoviruses (bean golden mosaic begomovirus, BGMV, and tomato mottle begomovirus, ToMoV) were inoculated to the cell cultures independently and detected by labeling by an indirect immunofluorescence technique. The viruses were detected bound to the cell membranes and within the cell cytoplasm. This is the first report of a continuous cell line established from a species of whitefly and its inoculation with two begomoviruses. The successful inoculation of whitefly cell cultures with begomoviruses shown in our results represents great promise for the development of systems that allow researchers to achieve a better understanding of the complex relationship between begomoviruses and their whitefly vectors.

The GroEL protein of the whitefly Bemisia tabaci interacts with the coat protein of transmissible and nontransmissible begomoviruses in the yeast two-hybrid system

We have previously suggested that a GroEL homolog produced by the whitefly Bemisia tabaci endosymbiotic bacteria interacts in the insect hemolymph with particles of Tomato yellow leaf curl virus from Israel (TYLCV-Is), ensuring the safe circulative transmission of the virus. We have now addressed the question of whether the nontransmissibility of Abutilon mosaic virus from Israel (AbMV-Is) is related to a lack of association between GroEL and the virus coat protein (CP). Translocation analysis has shown that, whereas TYLCV-Is DNA is conspicuous in the digestive tract, hemolymph, and salivary glands of B. tabaci 8 h after acquisition feeding started, AbMV-Is DNA was detected only in the insect digestive tract, even after 96 h. To determine whether AbMV-Is particles were rapidly degraded in the hemolymph as a result of their inability to interact with GroEL, we have isolated a GroEL gene from B. tabaci and used a yeast two-hybrid assay to compare binding of the CP of TYLCV-Is and AbMV-Is to the insect GroEL. The yeast assay showed that the CPs of the two viruses are able to bind efficiently to GroEL. We therefore suggest that, although GroEL-CP interaction in the hemolymph is a necessary condition for circulative transmission, the nontransmissibility of AbMV-Is is not the result of lack of binding to GroEL in the B. tabaci hemolymph, but most likely results from an inability to cross the gut/hemolymph barrier.

Phylogenetic relationships of world populations of Bemisia tabaci (Gennadius) using ribosomal ITS1

A phylogeny of Bemisia tabaci is presented based on the ITS1 region of ribosomal DNA. The monophyly of each biotype of Bemisia is supported, and a strong biogeographic pattern is evident in the data. Populations from the Americas (including the A biotype) form a clade sister to a clade comprising the silverleafing or B biotype and a nonsilverleafing biotype from the North Africa/Mediterranean region. Polymorphisms in rDNA suggest that silverleafing is a recent phenomenon, while the nonsilverleafing form is the ancestral or plesiomorphic state. Based on this phylogeny, if B. argentifolii is accepted as a separate species then one would have to review the taxonomic status of all biotypes of B. tabaci. In particular, a new name clearly would be needed for an Egypt/Spain/Sudan/Nigeria clade, and the monophyly of the haplotypes remaining in B. tabaci would be open to serious doubt. To make new species assignments in these circumstances seems premature. The phylogenetic relationships of the different populations of B. tabaci and the origins of effective natural enemies of the B biotype suggest that knowing the origin of the B biotype is not essential to finding effective agents and supports the notion that crop management is the key aspect to control.

Location of Geminiviruses in the Whitefly Bemisia tabaci (Homoptera: Aleyrodidae)

The location of tomato mottle virus (ToMoV) and cabbage leaf curl virus (CabLCV) (Geminiviridae, genus Begomovirus) in the whitefly vector Bemisia tabaci B-biotype (Homoptera: Aleyrodidae) was elucidated using a novel technique incorporating indirect immunofluorescent labeling in freshly dissected whiteflies. Begomoviruses were visualized in the whitefly by indirect-fluorescent-microscopy. Polyclonal and monoclonal primary antibodies were used to successfully detect both ToMoV and CabLCV. Both begomoviruses were located in the anterior region of the midgut and filter-chamber of adult whiteflies, with ToMoV detected in the salivary glands. CabLCV was detected at a greater frequency than ToMoV, with a positive detection of 16% (89 out of 560) for CabLCV and 3% (25 out of 840) for ToMoV. Possible sites involved in geminivirus transport from the gut lumen of whiteflies into the hemocoel were located in the filter-chamber and anterior portion of the midgut. The location of these begomoviruses suggests a possible scenario of virus movement through the whitefly, which is discussed.

Coat protein gene replacement results in whitefly transmission of an insect nontransmissible geminivirus isolate

Geminiviruses are transmitted by whiteflies, leafhoppers, or treehoppers. The whitefly species Bemisia tabaci (Gennadius) is the most efficient vector of Subgroup III geminiviruses. An isolate of Abutilon mosaic virus (AbMV), a bipartite geminivirus, was not detectable in the DNA extract from insects by Southern blot analysis, nor was the isolate transmissible by the B-biotype of B. tabaci, although the virus DNA was amplified (by PCR) from some insects. In contrast, Sida golden mosaic virus (SiGMV-Co), a closely related geminivirus, was acquired and transmitted by B. tabaci to various host plants. The coat protein of AbMV was replaced with that of SiGMV-Co. The resulting chimeric AbMV was acquired and transmitted to various host plants by B. tabaci, indicating that the coat protein plays an essential role in the transmission process by B. tabaci.