Interferon alpha contains a sequence motif similar to the complement receptor type two (CR2/CD21) binding site on complement fragment C3d. Antibodies against a peptide with the CR2 binding sequence on C3d react with a peptide carrying the IFN alpha CR2 binding motif (residues 92–99) and with recombinant IFN alpha. The IFN alpha‐derived peptide, as well as recombinant IFN alpha, inhibits C3bi/C3d interaction with CR2 on the Burkitt lymphoma Raji. The direct interaction of IFN alpha and CR2 is inhibited by polyclonal anti‐IFN alpha, anti‐CR2 and anti‐C3d peptide antibodies as well as by C3bi/C3d, EBV coat protein gp350/220 and IFN but not by IFN gamma. [125I]IFN alpha binding to Raji cells is inhibited by polyclonal anti‐IFN alpha and anti‐CR2 antibodies, by peptides with the CR2 binding motif and partially by C3bi/C3d. Monoclonal anti‐CR2 antibody HB5, but not OKB‐7, blocks IFN alpha binding to Raji cells. CR2 or CR2‐like molecules may therefore be the major IFN alpha receptors on B lymphocytes.

AbstractThe whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most important agricultural pests and virus vectors worldwide. Bemisia tabaci is considered a complex of cryptic species with at least 44 species. Among them, the species Middle East-Asia Minor 1 (MEAM1, formerly B biotype) and Mediterranean (MED, formerly Q biotype) are the most important, and they have attained global status. In Brazil, MEAM1 was first reported in the 1990s and is currently the predominant species in the country, meanwhile, MED was recently reported in the South and Southeast regions and was found to be mainly associated with ornamental plants. Currently, an increasing problem in the management of whitefly infestations in greenhouses associated with bell pepper was observed in São Paulo State, Brazil. The whiteflies were collected and identified based on a microsatellite locus (primer pair BEM23F and BEM23R) and the mitochondrial cytochrome oxidase I gene followed by restriction fragment length polymorphism analysis and sequencing. We observed that MED was the predominant species collected on bell pepper, but it was also found on tomato, cucumber, eggplant, and weeds grown in greenhouses. In open field, we found MED on tomatoes, bell peppers, and eggplants. In addition, MED was identified in Goiás State in association with ornamental plants. The begomovirus Tomato severe rugose virus and the crinivirus Tomato chlorosis virus was detected on bell pepper and tomato, respectively. Only MED specimens were found associated with the virus-infected plants. Moreover, we also investigated the endosymbionts present in the MED whiteflies. The collected populations of B. tabaci MED harbored a diversity of secondary endosymbionts, with Hamiltonella (H) found predominantly in 89 specimens of the 129 tested. These results represent a new concern for Brazilian agriculture, especially for the management of the newly introduced whitefly MED species, which must be implemented to limit the spreading and establishment of this pest in different crops in this country.

Lettuce mosaic virus (LMV) is transmitted by aphid vectors in a nonpersistent manner as well as by seeds. The virus causes severe disease outbreaks in commercial lettuce crops in several regions of Spain. The temporal and spatial patterns of spread of LMV were studied in autumn 2002 in the central region of Spain. Symptomatic lettuce (var. Cazorla) plant samples were collected weekly, first at the seedling stage from the greenhouse nursery and later outdoors after transplantation. The exact position of symptomatic plants sampled in the field was recorded and then material was tested by enzyme-linked immunosorbent assay to assess virus infection. Cumulative spatial data for infected plants at different growth stages were analysed using spatial analysis by distance indices. For temporal analysis, the monomolecular, Gompertz, logistic and exponential models were evaluated for goodness of fit to the entire set of disease progress data obtained. The results indicated that the disease progress curve of LMV epidemics in the selected area is best described by a Gompertz model and that the epidemic follows a polycyclic disease progression. Our data suggest that secondary cycle of spread occurs when noncolonising aphid species land on the primary infected plants (probably coming from infected seed) and move to adjacent plants before leaving the crop. The role of weeds growing close to lettuce fields as potential inoculum sources of virus and the aphid species most likely involved in the transmission of LMV were also identified.

Chaetosiphon fragaefolii (Cockerell) (Hemiptera: Aphididae) is the predominant aphid in strawberry (Fragaria × ananassa Duchesne) production systems in Brazil. This pest species directly damages the plants and is also responsible for spreading viruses. Further, C. fragaefolii often renders strawberry cultivation unviable, because of its high reproductive rate, as well as the large number of individuals generated through parthenogenesis. The present study aimed to (1) evaluate the feeding behavior of C. fragaefolii in four strawberry cultivars (Albion, Aromas, Camarosa, and San Andreas) and (2) identify the resistance factors associated with the number and type of trichomes in the cultivars, and also its effect on the feeding behavior of C. fragaefolii, using the electrical penetration graph (EPG) technique. The results revealed an intrinsic relationship between the number of trichomes on the cultivar and feeding behavior of C. fragaefolii. A higher number of trichomes, both tector and glandular, was observed in Albion compared to that of other cultivars, resulting in a longer no probing (Np) period per insect, and a longer Np phase. A relatively short phloem phase and ingestion time of the phloem sieve elements were also observed in Albion. These results suggest that the trichomes act as a physical barrier creating difficulties for C. fragaefolii to feed, thereby altering its feeding behavior in the four cultivars studied.

O coleóptero Cerotoma arcuata Oliv. (1791), "vaquinha-preta-e-amarela-da-soja", é descrito no Brasil como vetor de diversos vírus que infectam leguminosas, entre eles o vírus do mosaico severo do caupi ("cowpea severe mosaic Comovirus" - CpSMV). Em 1991, detectou-se uma infecção viral em plantas de Vigna luteola Jacq. (Leguminosae), coletadas no município de Praia Grande, no litoral Sul do Estado de São Paulo e, posteriormente, o vírus foi identificado como um isolado deste Comovirus. Visando fornecer subsídios a uma melhor compreensão do processo de transmissão do fitovírus isolado de V. luteola (CpSMV-SP), foram feitas tentativas de transmissão por diferentes artrópodos, incluindo sete espécies de insetos e uma de ácaro. Determinaram-se altas taxas de transmissão (46,6, 50,0 e 70,0%) do CpSMV-SP em plantas de feijão, por adultos de C. arcuata. O vírus foi transmitido ainda por larvas de 1° ínstar, com taxas de 10,0% (caupi) e 40,0% (feijoeiro). Ausência de transmissão foi constatada nos ensaios por artrópodos pertencentes a outras ordens (Hemiptera: Aleyrodidae, Aphididae; Acari: Tetranychidae; Thysanoptera: Thripidae) e outras espécies de coleópteros (Diabrotica bivittula, D. speciosa e Epicauta atomaria).

Insect-borne plant viruses usually alter the interactions between host plant and insect vector in ways conducive to their transmission (‘host manipulation hypothesis’). Most studies have tested this hypothesis with persistently and non-persistently transmitted viruses, while few have examined semi-persistently transmitted viruses. The crinivirus Tomato chlorosis virus (ToCV) is semi-persistently transmitted virus by whiteflies, and has been recently reported infecting potato plants in Brazil, where Bemisia tabaci Middle East Asia Minor 1 (MEAM1) is a competent vector. We investigated how ToCV infection modifies the interaction between potato plants and B. tabaci in ways that increase the likelihood of ToCV transmission, in two clones, one susceptible (‘Agata’) and the other moderately resistant (Bach-4) to B. tabaci. Whiteflies alighted and laid more eggs on ToCV-infected plants than mock-inoculated plants of Bach-4. When non-viruliferous whiteflies were released on ToCV-infected plants near mock-inoculated plants, adults moved more intensely towards non-infected plants than in the reverse condition for both clones. Feeding on ToCV-infected plants reduced egg-incubation period in both clones, but the egg–adult cycle was similar for whiteflies fed on ToCV-infected and mock-inoculated plants. Our results demonstrated that ToCV infection in potato plants alters B. tabaci behaviour and development in distinct ways depending on the host clone, with potential implications for ToCV spread.

-Aphids are the most important vectors of viruses infecting potato (Solanum tuberosum).We focused on the response of the aphid vector Myzus persicae (Sulzer) to fi ve commercial potato cultivars: Ágata, Jaette Bintje, Mondial, Monalisa and Santè, by traditional antibiosis and antixenosis tests and by the EPG (Electrical Penetration Graph) technique, as a step forward to the design of effective management practices. Our aim was to identify plant factors involved in resistance of these cultivars against M. persicae, both at the surface and in deeper plant tissues. Results from the antixenosis test confi rmed a strong preference of M. persicae for the Mondial cultivar. The antibiosis study indicated a lower population development of the aphid in 'Monalisa' when compared to 'Ágata' and 'Jaette Bintje'. EPG assays indicated that 'Santè' inhibited the initial feeding process of M. persicae, whereas 'Monalisa' showed a physical-type of resistance as demonstrated by a very high number of short probes. The cultivar Mondial showed average values for all EPG variables analyzed. The behavior in 'Jaette Bintje' indicated this cultivar was an ideal host for aphid feeding and reproduction. Together, the EPG data revealed the existence of pre and post-phloematics factors in the cultivars under study, which have important implications on the effi ciency of transmission and spread of virus in potato by M. persicae. KEY WORDS: Electrical penetration graph, EPG, Solanum tuberosum, host plant resistanceAs doenças virais na cultura de batata geralmente são letais às plantas hospedeiras e, quando associadas às condições climáticas do Brasil, normalmente favoráveis à proliferação dos afídeos, seus principais insetos vetores, podem causar o início de uma epidemia que pode acarretar em perda de produção (Salas et al 2004). Os principais responsáveis pela degenerescência da batata-semente no país são o "vírus Y da batata" (Potato virus Y, PVY) e o "vírus do enrolamento da folha da batata" (Potato leafroll virus, PLRV) (Figueira 1995, Souza Dias 1995. As interações envolvendo afídeos e plantas são de extrema importância ao se estudar a transmissão de fi tovírus, visto que a habilidade de transmitir o patógeno está intimamente relacionada à atividade estiletar e hábito alimentar do inseto vetor.Sabe-se que alguns vírus, principalmente os de transmissão não-persistente, são adquiridos e inoculados de maneira muito rápida (segundos/minutos), como o PVY e seus isolados, não sendo necessário que o vetor ultrapasse a epiderme e o mesofi lo onde os mesmos se concentram. Por outro lado, os vírus de transmissão persistente, como o PLRV, geralmente necessitam de maior período, tanto para a aquisição quanto para inoculação (várias horas), por se situarem principalmente no fl oema das plantas, demandando do afídeo maior fi xação na planta e um longo trabalho estiletar

RESUMO: Quatro isolados do vírus do mosaico da berinjela (EMV -"eggplant mosaic virus" -grupo tymovírus) foram armazenados a partir de extra tos foliares de hospedeiras com sintomas sistêmicos. Os virus EM V-AI (isolado de Abelia), EMV-Sc (isolado da Escócia), -ts (estirpe-padrão) e VNBT (vírus da necrose branca do tomateiro), que induzem sintomas em Chenopodium amaranticolor, C. murale, C.quinoa (Família Chenopodiaceae) Datura stramonium, Lycopersicon esculentum e Nicotiana glutinosa (Solanaceae), foram conservados em extra tos destas plantas, à temperatura ambiente, em geladeira e em congelador. A infectividade dos vírus, em diferentes períodos de armazenamento, foi testada em plantas de datura e glutinosa, para se determinar a longevidade in vitro. Constatou-se que, quando guardados em baixas temperaturas,os extra tos preservam por mais tempo a infectividade dos vírus. No caso de datura e glutinosa, por exemplo, resultados positivos foram obtidos até 413 e 282 dias de armazenamento, respectivamente, em congelador. Entretanto, com relação às espécies de Chenopodium testadas, mesmo alguns extra tos recém-preparados conduziram a resultados negativos, confirmando a presença de inibidores de infecção virai nestas plantas. Das três espécies, é sugerida a utilização apenas de C.quinoa para o preparo de extra tos visando preservar estes vírus e, assim mesmo, por um período relativamente curto (entre 53 e 80 dias) . A avaliação geral dos resultados mostra que, para os tymovírus estudados neste trabalho, é possível conservar a infectividade através da técnica de armazenamento de extra tos foliares de plantas sistemicamente infectadas.Palavras-chave: tymovírus, armazenamento em extra tos, Solanaceae, Chenopodiaceae