{"id":162468,"date":"2014-12-27T14:31:00","date_gmt":"2014-12-27T16:31:00","guid":{"rendered":"http:\/\/revistapesquisa.fapesp.br\/?p=162468"},"modified":"2015-01-27T14:44:30","modified_gmt":"2015-01-27T16:44:30","slug":"vegetarian-vampire","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/vegetarian-vampire\/","title":{"rendered":"Vegetarian vampire"},"content":{"rendered":"

\"\"<\/a>Mites of the genus Brevipalpus<\/em>, which number over 200 known species, are nearly invisible to the naked eye. They measure only 0.3 millimeter in size and, if placed on a sheet of paper, they would be smaller than the period at the end of this sentence. They generally adapt well to various environmental and climatic conditions\u2014they can withstand harsh winters, for example\u2014but they prefer tropical areas with milder temperatures. They can infest more than a thousand plant species and become a pest when they spread in large numbers in crops of tea or grapes. One of the most harmful effects of these mites is that they spread disease-causing viruses in orchids, passion fruit, coffee and orange crops. Some viruses initially cause spots on leaves, fruit and branches, but they can kill the plant. Estimates indicate that in recent years, orange growers in the state of S\u00e3o Paulo, the world\u2019s largest producer of orange juice, have spent $80 million per year to control Brevipalpus phoenicis<\/em>, the species that spreads the citrus leprosis virus in orange trees.<\/p>\n

In an effort to find more effective ways to minimize such losses, Brazilian agronomist Elliot Kitajima of the University of S\u00e3o Paulo (USP) and German zoologist Gerd Alberti of the University of Greifswald decided to research how the mites acquire this virus and then transmit it to plants. \u201cWe now have more accurate information on the steps involved in this mechanism of acquisition and transmission, although many details still need clarification,\u201d says Kitajima, who conducts research in the Department of Phytopathology and Nematology at USP\u2019s Luiz de Queiroz College of Agriculture (ESALQ).<\/p>\n

In the case of citrus leprosis, like a vampire that becomes contaminated by sucking the blood of an infected person, the Brevipalpus<\/em> mite becomes infected with the virus when it consumes the cell contents, or cell juice, of the leaves of a sick orange tree. The virus travels through the mite\u2019s digestive system without reproducing, and it is then passed on when the Brevipalpus<\/em> feeds on a healthy plant, as shown in the findings presented in a series of papers published in 2014 in the journal Zoologica<\/em>. \u201cThe paper also presents a taxonomic review of Brevipalpus<\/em> and assesses the economic losses caused by the mite,\u201d Alberti says. \u201cThis is probably the most in-depth study of the internal structures of these mites ever conducted,\u201d he says.<\/p>\n

Kitajima has studied the viruses transmitted by Brevipalpus<\/em> mites since the 1970s when he was at the University of Bras\u00edlia, and he moved to ESALQ in 1995. In the mid-2000s, however, he came to an impasse. \u201cWe were able to visualize the virus inside the mite, but we didn\u2019t know enough about its anatomy to pinpoint precisely where in the mite the virus could be found,\u201d he says. In 2006 he decided to contact Alberti, one of the world\u2019s leading authorities on the subject, and Alberti accepted the challenge of researching the internal details of Brevipalpus <\/em>mites.<\/p>\n

It took seven years of intensive, meticulous work. The researchers produced very thin sections of the mites and analyzed them using powerful electron microscopes. They also had to do a three-dimensional reorganization of the anatomical structures\u2014\u201ca veritable tomography,\u201d says Kitajima\u2014to find the exact location of the virus in the organs and tissues. \u201cIt\u2019s as if we cut a sausage and observed the spatial distribution of the bits of fat, which would correspond to the viruses,\u201d he notes by way of comparison.<\/p>\n

Voyage through the body
\n<\/strong>Using this strategy, they confirmed that Brevipalpus<\/em> ingests the virus when it uses its stylet\u2014a needle-like extension of the mouth apparatus that has only now been described in detail in these mites\u2014to pierce the leaves of orange trees. The virus enters the highly branched intestine (cecum) of the mite along with the food, and it lodges between membranes of adjacent epithelial or glandular cells\u2014rather than inside of them, as had been suspected. This observation indicates that the citrus leprosis virus travels through the body of the mite but does not reproduce in its tissues. \u201cWe don\u2019t know for sure how the virus exits the cecum to the space between the cells and moves on from there to the stylet canal, through which it is injected along with the mite\u2019s saliva into the cells of healthy leaves,\u201d explains the ESALQ researcher.<\/p>\n

Kitajima and Alberti were assisted by the group headed by Jo\u00e3o Spotti Lopes, an entomologist at ESALQ, as they sought to achieve a better understanding of the mite\u2019s feeding process. Laura Garita, a master\u2019s student under Kitajima, was able to attach onto the back of the mite a fine gold wire connected to an electrical circuit attached to the plant. Whenever the mite fed, the circuit closed and the electrical current was recorded on a computer. This process enabled her to determine the duration of each feeding phase\u2014insertion of the stylet, salivation and suction. The mite takes an average of four hours to acquire the virus when feeding on a contaminated leaf, and about two hours to inoculate the virus into healthy tissue during another meal. Although viruses do not reproduce in Brevipalpus<\/em>, the mite can carry them for a long time (10 days), even if it does not have access to new virus sources. The researchers also observed that viruses transmitted by Brevipalpus<\/em> appear to produce only localized lesions, probably because it doesn\u2019t inoculate the virus into the plant\u2019s vascular system.<\/p>\n

\u201cThese data are critical for completing the epidemiology, in order to understand how the virus is spread in nature and guide more intelligent and effective pest control initiatives,\u201d Kitajima points out. He explains that the viral activity is generally limited, and it spreads slowly. \u201cIn orchards, therefore, it would be sufficient to focus control efforts on contaminated and surrounding plants; there is no need to spray insecticide on the entire crop.\u201d<\/p>\n

In the collection of articles, Kitajima prepared one that is a review of the biology of Brevipalpus<\/em>, and another on the mite-virus relationship. Alberti handled the ones that focus on anatomical details and the functioning of the digestive and reproductive systems.<\/p>\n

Kitajima now plans to find and characterize other viruses transmitted by Brevipalpus <\/em>mites, expand research on the taxonomy and evolution of these arachnids, and study potential biological controls (natural predators). \u201cWe are talking with growers and sharing our discoveries with them,\u201d he says. \u201cIn the case of citrus leprosis, we want to find the best strategies for achieving maximum reduction of orange crop expenditures.\u201d<\/p>\n

Projects<\/strong>
\n1.<\/strong> Management of citrus leprosis (No. 08\/52691-9<\/a>); Grant mechanism <\/strong>Thematic project; Principal investigator<\/strong> Elliot Watanabe Kitajima (ESALQ\/USP); Investment<\/strong> R$576,462.69 (FAPESP).
\n2.<\/strong> Characterization of plant viruses transmitted by the false spider mite Brevipalpus spp. (Tenuipalpidae) and studies on the virus\/vector\/plant relationship (No. 00\/11805-0<\/a>); Grant mechanism<\/strong> Thematic project; Principal investigator<\/strong> Elliot Watanabe Kitajima (ESALQ\/USP); Investment<\/strong> R$362,063.71 (FAPESP).<\/p>\n

Collection of scientific articles
\n<\/em>ALBERTI, G. & KITAJIMA, E. W. (eds.). Anatomy and fine structure of Brevipalpus mites (Tenuipalpidae) \u2013 Economically Important Plant-Virus Vectors<\/a>. Zoologica<\/strong>. v. 160. p. 1-192. May\u00a02014.
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