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The genera Daidalotarsonemus De Leon and Excelsotarsonemus Ochoa & Naskrecki are mainly characterized, in the females, by the presence of sculpturing on the dorsal shields and by highly modified dorsal setae, greatly enlarged, laminar or sail-shaped. Moreover, both genera are characterized by abundant cerotegument all over the body and on the modified setae (d, e, f) with the presence of fungi, lichens, and bacteria accumulating. The peculiar morphology of the dorsal setae in these two genera has suggested they might have other functions beside the sensory one. Ultrastructural observations using scanning and transmission electron microscopy techniques revealed that, albeit extravagantly modified, these dorsal setae should act as mechanoreceptors in agreement with most of the previous observations in mites. The morphological modifications of the setae d, e, and f (pronounced cup shape of setae e and enlarged shaft with concave longitudinal strips of setae d and f) suggest they play, in addition to the tactile function, a storage role and dispersive role for fungal spores collected by the mite while moving in the humid environment. Moreover, the modified setae d, e, and f inserted on elevated sockets are probably movable by the action of dorso-ventral muscles; thus, mites might use their sail-shape to become airborne. In addition, the body dorso-ventral muscles observed inserting close to the elevated seta e sockets suggest the mite might also lift these cup-like setae to spread the fungal particles on the body or over adjacent vegetation as well. Biological and feeding studies are necessary to better understand the role such fungi might play in the mite life cycle., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The setae of mites are not regarded as secretory structures, yet in the flat mite genus Raoiella, each developmental stage presents droplets of fluid associated with the tips of their dorsal setae. To understand the origin of this fluid, the ultrastructure of the dorsal setae is investigated in females of Raoiella bauchani Beard & Ochoa and the invasive pest species Raoiella indica Hirst using scanning and transmission electron microscopy techniques. The dorsal setae are barbed along their entire length and have either a broadened plumose or a flat spatulate tip. Ultrastructurally, they present the typical features of mechanoreceptors, but have a "hollow" axis represented by a protoplasmatic core containing dendritic branches. This combination of ultrastructural characters indicates that the setae might be multimodal receptors: acting as both mechanoreceptors and contact chemoreceptors. The epidermal cells that underlie the setal sockets are columnar and have an ultrastructure that suggests they have a glandular function. Moreover, these cells present regular microvilli apically and form extracellular cuticular canals, containing epicuticular filaments, that are connected with the microvilli proximally and which open via pores onto the surface of the setal base distally. This arrangement indicates that the secretion from the microvilli passes into the canals and is then conducted to pores at the base of the seta, where it then accumulates and moves up the setal shaft, along the longitudinal grooves of the barbs. Based on similar arrangements in some insect taxa, the organization of the structures here observed in Raoiella suggests the passage of a non-polar, water insoluble, lipoid fluid through the cuticle, the function of which is still obscure., Competing Interests: Declaration of competing interest The authors have no competing interests to declare., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The genus Brevipalpus (Tenuipalpidae) includes 291 described species commonly found in the tropical and subtropical regions. Morphological characters considered in the taxonomy of Brevipalpus species are difficult to discern, which often leads to erroneous identifications and the presence of cryptic species within species is suspected. New morphological characters are now considered relevant for identification of Brevipalpus species; among them, the morphology of the seminal receptacle (spermatheca) of the female insemination system. This feature has not been considered relevant until now; thus, there is little information about the insemination system in the available species descriptions. Hence, in the present study, ultrastructural details are provided for the insemination system in five species of Brevipalpus, representing different morphological groups. The seminal receptacle (spermatheca) and the insemination duct are illustrated using light, transmission and scanning electron microscopy. The spermatheca proved to have specific morphological features that can be useful for taxonomic purposes. On the other hand, its appearance within a population might be variable in a way that needs to be ascertained and evaluated.

A group of related bacilliform, nuclear viruses with a bisegmented negative-sense RNA genome that are transmitted by Brevipalpus mites likely in a circulative-propagative manner were recently classified in the new genus Dichorhavirus, family Rhabdoviridae. These viruses cause localized lesions on leaves, stems, and fruits of economically significant horticultural and ornamental plant species. Among its members, orchid fleck virus, citrus leprosis virus N, and coffee ringspot virus are most prominent. This chapter summarizes the current knowledge about these viruses, available detection techniques, and their interactions with their plant hosts and mite vectors., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Brevipalpus (Acari: Tenuipalpidae) mites are important pests on a variety of host plant species. The mites damage their hosts directly by feeding and some species also serve as vectors of plant viruses. Among more than 200 described Brevipalpus species, three are recognized as vectors of plant viruses: B. phoenicis, B. californicus and B. obovatus. These species occur worldwide in subtropical and tropical regions. Brevipalpus mites reproduce mostly by thelytokous parthenogenesis and this condition was attributed to a bacterial endosymbiont, recently characterized as a member of the genus Cardinium. The same symbiont infects many other arthropods and is capable of manipulating their host reproduction in various ways. Generally the presence of Cardinium is determined by molecular, PCR based, techniques. In the current work we present visual evidence for the presence of these bacteria by transmission electron microscopy as a complement of previous detection by PCR. Cardinium is easily identified by the presence of a unique array of microtubule-like structures (ML) in the cell. Symbionts have been observed in several organs and eggs from different populations of all three Brevipalpus species known as vector of plant viruses. Cardinium cells were always immersed directly within the cytoplasm of infected cells. Bacteria were observed in all females of all instars, but were absent from all males examined. Females from some Brevipalpus populations were observed to be uninfected by Cardinium. This observation confirmed previous PCR-based results that these populations were aposymbiotic. The observed distribution of the bacteria suggests that these bacteria could have other functions in the mite biology beside feminization.

A decade ago, a new mite-transmitted disease was described on wheat (Triticum aesativum) and maize (Zea mays) that due to its geographical location was referred to as High Plains Disease (HPD). To determine the etiology, we established colonies of HPD pathogen-transmitting eriophyid wheat curl mites (Aceria tosichella) on wheat plants for maintenance of a continuous source of infected material. Analyses of nucleic acid obtained from infected plants showed the presence of HPD-specific RNAs ranging from 1.5 to 8 kilobases, but comparisons between the sequence of cDNAs and the databases did not reveal any clear identity with known viruses. We demonstrate that a diagnostic HPD-specific 32-kDa protein that accumulates in plants is encoded by a small RNA species (RNA-s). Upon infestation of upper wheat parts with viruliferous mites, the RNA-s encoded protein becomes detectable within a few days in the roots, indicative of an effective virus-like mode of transport. Membranous particles, resembling those observed in thin sections of infected plants, were isolated and shown to envelope a thread-like ribonucleoprotein complex containing the RNA-s encoded 32-kDa protein. This complex was associated with single-stranded (-)-sense RNAs, whereas free (+)-sense RNA was only detected in total RNA of infected plants. Based on the collective properties, we conclude that HPD is caused by a newly emerged mite-borne virus, for which we propose the name Maize red stripe virus (MRStV).

The flat mite genus Raoiella Hirst (Tenuipalpidae) has attracted considerable research interest due to the rapid spread of Raoiella indica Hirst which feeds most commonly on species of palms (Arecaceae). Raoiella are frequently observed with their stylets inserted into the leaf stomatal openings, suggesting they feed on this site. Herein, we use transmission electron microscopy (TEM), scanning electron microscopy (SEM), low temperature scanning electron microscopy (LTSEM) and light microscopy (LM) to describe the mouthpart organization and the feeding behavior found in R. indica and R. bauchani Beard & Ochoa. The feeding mechanism is also discussed based on their distinctive morphological aspects. The structure of the gnathosoma of Raoiella generally agrees with the organization previously observed in Brevipalpus and Cenopalpus. As in other tetranychoid mites, there is no anatomical connection between the inter-stylet tube and the food channel, corroborating the theory that the stylets are used to pierce plant tissue (and assumedly inject saliva) but play no role in sucking up fluid from damaged host cells. As in Brevipalpus, the adoral setae are mechanoreceptors that may help guide the mite to the site for feeding. The ultrastructure of supracoxal setae e remains enigmatic. We also present observations of possible epidermal feeding on Phoenix roebelenii O'Brien (Arecaceae) for R. indica. Raoiella indica were shown to penetrate both the guard cells of the stomata and the epidermis of P. roebelenii, suggesting that feeding via the epidermis could be possible on this host plant. [ABSTRACT FROM AUTHOR]