Circulative Transmission of Cileviruses in Brevipalpus Mites May Involve the Paracellular Movement of Virions.

Plant viruses transmitted by mites of the genus Brevipalpus are members of the genera Cilevirus, family Kitaviridae, or Dichorhavirus, family Rhabdoviridae. They produce non-systemic infections that typically display necrotic and/or chlorotic lesions around the inoculation loci. The cilevirus citrus leprosis virus C (CiLV-C) causes citrus leprosis, rated as one of the most destructive diseases affecting this crop in the Americas. CiLV-C is vectored in a persistent manner by the flat mite Brevipalpus yothersi. Upon the ingestion of viral particles with the content of the infected plant cell, virions must pass through the midgut epithelium and the anterior podocephalic gland of the mites. Following the duct from this gland, virions reach the salivary canal before their inoculation into a new plant cell through the stylet canal. It is still unclear whether CiLV-C multiplies in mite cells and what mechanisms contribute to its movement through mite tissues. In this study, based on direct observation of histological sections from viruliferous mites using the transmission electron microscope, we posit the hypothesis of the paracellular movement of CiLV-C in mites which may involve the manipulation of septate junctions. We detail the presence of viral particles aligned in the intercellular spaces between cells and the gastrovascular system of Brevipalpus mites. Accordingly, we propose putative genes that could control either active or passive paracellular circulation of viral particles inside the mites.

Lethal and sublethal effects of insecticides on the survival and reproduction of Brevipalpus yothersi (Acari: Tenuipalpidae).

The overuse of insecticides to control vector insects such as Diaphorina citri Kuwayama in citrus groves has altered the population dynamics of pest mites. Among phytophagous mites, population outbreaks of citrus leprosis mite, Brevipalpus yothersi Baker, have been increasingly intense and frequent in Brazilian citrus groves. Despite the great importance of the B. yothersi mite for citrus production, the lethal and sublethal effects of insecticides on this mite have not yet been studied. Therefore, in this study, the effects of insecticides commonly used for D. citri control on B. yothersi mortality, reproduction, and instantaneous growth rate were assessed. For this, two experiments were carried out, one under controlled conditions and another in a greenhouse. The insecticides tested were beta-cyfluthrin, bifenthrin, buprofezin, chlorpyrifos, dimethoate, pyriproxyfen, and thiamethoxam at 0 (control), 0.0625, 0.125, 0.25, 0.5, 1, and twofold the recommended insecticide concentration for D. citri control. The pyriproxyfen insecticide provided high mortality of B. yothersi even at low concentrations. Furthermore, this insecticide negatively interfered with the reproduction of this mite. Beta-cyfluthrin, bifenthrin, buprofezin, chlorpyrifos, dimethoate, and thiamethoxam, in the tested concentrations, showed low impact on citrus leprosis mite. Regarding the reproduction of the mite, no significant increase in fecundity was observed on B. yothersi females exposed to insecticide residues, regardless of the concentration tested. Therefore, the application of these insecticides in the management of pest insects is unlikely to promote an increase in the citrus leprosis mite population.

Resistência de Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) a acaricidas inibidores da respiração celular em citros: resistência cruzada e custo adaptativo / Resistance of Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) to acaricides that inhibit cellular respiration in citrus: cross-resistance and fitness cost

Acaricidas inibidores da respiração celular são importantes para o controle de Brevipalpus phoenicis (Geijskes) na cultura dos citros no Brasil. Foram conduzidos estudos para avaliar: (a) a variabilidade na suscetibilidade de populações de B. phoenicis coletadas em pomares de citros para cihexatim, azociclotim, propargite e enxofre; (b) relações de resistência cruzada entre propargite e os acaricidas azociclotim, cihexatim, dinocape, piridabem e enxofre; e (c) o custo adaptativo associado à resistência de B. phoenicis a propargite em condições de laboratório. O método de bioensaio adotado foi o contato residual. A suscetibilidade foi estimada com concentrações diagnósticas baseadas na CL95 de cada acaricida. A resistência cruzada foi avaliada pela caracterização da curva de concentração-mortalidade das linhagens suscetível (S) e resistente a propargite (Propargite-R). O custo adaptativo foi avaliado mediante comparação de parâmetros biológicos das linhagens S e Propargite-R em frutos de laranja a 25 ± 1°C e fotofase de 14h. Diferenças significativas na sobrevivência de B. phoenicis foram verificadas aos acaricidas cihexatim (de 16,3 por cento a 80,5 por cento), azociclotim (de 3,0 por cento a 15,0 por cento), propargite (de 1,0 por cento a 71,6 por cento) e enxofre (de 9,0 por cento a 82,6 por cento). Baixa intensidade de resistência cruzada foi verificada entre propargite e os acaricidas azociclotim (1,8 vezes), cihexatim (4,6 vezes), dinocape (3,5 vezes) e piridabem (3,5 vezes). Por outro lado, a intensidade de resistência cruzada a enxofre (> 111 vezes) foi bastante alta. Não foi verificada presença de custo adaptativo associado à resistência de B. phoenicis a propargite. Portanto, o uso desses acaricidas também deve ser feito de maneira criteriosa no manejo da resistência de B. phoenicis a acaricidas.

Acaricides that inhibit cellular respiration play an important role in the control of Brevipalpus phoenicis (Geijskes) in citrus groves in Brazil. Studies were conducted to evaluate: (a) the variability in the susceptibility among B. phoenicis populations collected from citrus groves to cyhexatin, azocyclotin, propargite and sulphur; (b) cross-resistance relationships between propargite and azocyclotin, cyhexatin, dinocap, pyridaben and sulphur; and (c) the fitness cost associated with propargite resistance in B. phoenicis under laboratory conditions. A residual-type contact bioassay was used to characterize the susceptibility. The susceptibility was estimated with diagnostic concentrations based LC95 of each acaricide. The cross-resistance was evaluated by characterizing the concentration-mortality responses of susceptible (S) and propargite-resistant (Propargite-R) strains. The fitness cost was evaluated by measuring the biological parameters of S and Propargite-R strains on citrus fruits at 25 ± 1°C and fotophase of 14h. Significant differences in the susceptibility of B. phoenicis were detected at diagnostic concentration of cyhexatin (survivorship from 16.3 percent to 80.5 percent), azocyclotin (from 3.0 percent to 15.0 percent), propargite (from 1.0 percent a 71.6 percent) and sulphur (from 9.0 percent to 82.6 percent). A low intensity of cross-resistance was detected between propargite and the acaricides azocyclotin (1.8-fold), cyhexatin (4.6-fold), dinocap (3.5-fold) and pyridaben (3.5-fold). On the other hand, the intensity of cross-resistance to sulphur (> 111-fold) was very high. There was no fitness cost associated with B. phoenicis resistance to propargite, based on biological parameters evaluated. Therefore, the use of these acaricides should also be done very carefully in resistance management of B. phoenicis to acaricides.

Brevipalpus mites Donnadieu (Prostigmata: Tenuipalpidae) associated with ornamental plants in Distrito Federal, Brazil

Brevipalpus mites colonize a great number of fruit and ornamental plants. Mite species belonging to this genus have been associated with many plant viruses. Citrus leprosis (CiLV) is the most economically important virus transmitted by B. phoenicis mites. It has recently been shown that ornamental plant species can be alternative hosts of this virus. The high volume of trade and frequent movement of live ornamental plants make them efficient pest disseminators. Because of this, it is desirable to expand knowledge of potential pests aiming to guide the adoption of quarantine measures. This work reports ornamental plant hosts of Brevipalpus mites in the Distrito Federal (DF), as well the occurrence of symptoms consistent with Brevipalpus-borne plant viruses in these same hosts. Between July and September of 2005, five surveys were carried out in 14 localities within DF. Leaves and branches of fifty-five ornamental plant species were sampled. The species Pithecellobium avaremotemo Mart. is for the first time reported as a host for B. phoenicis (Geijskes), B. californicus Banks and B. obovatus Donnadieu species. Additionally, seven new species are reported as hosts for Brevipalpus within South America. New hosts are also listed for individual mite species. Typical symptoms of Brevipalpus-borne viruses were observed in Ligustrum sinense Lour., Pelargonium hortorum L.H. Bailey, Hibiscus rosa-sinensis L. and orchids (Dendrobium and Oncidium). The results of this work emphasize the potential role of the ornamental plants as vehicles for dissemination of Brevipalpus mites.

Os ácaros do gênero Brevipalpus colonizam um grande número de espécies frutíferas e ornamentais e têm sido associados a viroses de muitas plantas. A leprose dos citros é a virose de maior importância econômica transmitida por esses ácaros. Recentemente foi comprovado que algumas plantas ornamentais podem ser hospedeiras alternativas desse vírus. Os grandes volumes e a alta movimentação das plantas ornamentais fazem com que estas ajam como eficientes disseminadoras de pragas. Por essa razão, é necessário ampliar o conhecimento sobre pragas potenciais, de modo a subsidiar a implementação de medidas quarentenárias. Neste trabalho são relatadas as plantas ornamentais hospedeiras de ácaros Brevipalpus no Distrito Federal, assim como a ocorrência de sintomas típicos de viroses a elas transmitidas por Brevipalpus. Entre julho e setembro de 2005, foram realizadas cinco coletas em 14 localidades do DF. Foram amostradas folhas e ramos de 55 espécies de ornamentais. Pithecellobium avaremotemo Mart. é relatada, pela primeira vez, como hospedeira das espécies B. phoenicis (Geijskes), B. californicus Banks e B. obovatus Donnadieu. Adicionalmente, são relatadas sete novas espécies como hospedeiras de Brevipalpus na América do Sul. Novos hospedeiros são também listados para cada uma das espécies. Sintomas típicos de viroses transmitidas por Brevipalpus foram observados em Ligustrum sinense Lour., Pelargonium hortorum L.H. Bailey, Hibiscus rosa-sinensis L. e orquídeas (Dendrobium e Oncidium). Os resultados deste trabalho enfatizam o papel potencial de plantas ornamentais como veículo para disseminação de ácaros Brevipalpus.