Stylostome organization in feeding Leptotrombidium larvae (Acariformes: Trombiculidae)

Abstract

The stylostome of larvae of the trombiculids Leptotrombidium scutellare (Nagayo et al.), Leptotrombidium fletcheri (Womersley et Heaslip) and Leptotrombidium deliense (Walch) was studied experimentally at different time intervals after larval attachment using the histological method. The stylostome of these species has the same organization and belongs to the epidermal combined with the mixed type, developing more in width than in length. Neither transverse nor conspicuous longitudinal layers are present within the stylostome walls, which stain predominantly in red with Azan, also showing longitudinal portions with blue staining. Larvae tend to attach closely to each other and scabs, consisting of the hyperkeratotic epidermal layers fusing with migrating inflammatory cells, develop around the attachment sites. The dermis shows inflammatory foci with dilated capillaries and inflammatory cells inserting in the connective tissue layer underneath the stylostome. The feeding cavity, which is moderately expressed, may be found either in the epidermis or in the dermis. It contains inflammatory cells and their debris in the liquefied host tissues. The stylostome length depends on the character of the attachment site (the thicker epidermis or scab the longer the stylostome), and does not directly correspond to the stages of larval feeding. Nevertheless, at the 48-h time interval, nearly all attached larvae are found to be fully fed and their midgut cells are filled with nutritional globules.

The Role of Chiggers as Human Pathogens

“…In lizards, specific adaptive structures of skin, known as "mite pockets", may evolve to decrease the possible damage from mite feeding [38]. It is generally thought that the organization and location of stylostome is species specific in trombiculid larvae, irrespectively of the host species and of the particular feeding site on the host, whereas the length of the stylostome is mostly a result of the width of the epidermal layer and the presence or absence of scabs at the attachment site [39].…”

“…These salivary components generally reveal relatively moderate lytic properties and weak immunological characters [111]. The type of skin inflammatory response during the feeding of trombiculid larvae is determined by concomitant factors such as the site of the parasite localization, condition of the host's skin, among others [39]. Repeated exposures result in a more rapid and intense adaptive immune response [102].…”

“…However, the occurrence of unusual outbreaks of urticaria, increasingly severe pruritus or bulla formation, are indications of hypersensitivity to such antigenic substances [5]. It is clear that the natural hosts of trombiculids have to be sensitized with respect to parasites that may lead the development of the strong specific inflammatory response [39,111].…”

Stylostome formation by parasitic larvae of Allothrombium fuliginosum (Trombidiformes: Trombidiidae): morphology of feeding tubes and factors affecting their size

“…Parasitism by larvae of some Parasitengona mites is associated with the formation of stylostomes (feeding tubes) in the hosts’ tissues. Larvae feed on the host's haemolymph and liquefied host material (Peterson et al 1992 ; Wohltmann 2000 ; Shatrov 2009 ; Shatrov et al 2014 ). There has been much debate as to whether the stylostomes are organs of the mites, salivary secretions of the mite, a reaction by the host, or a combination of the latter two, but the current consensus is that they result from salivary secretions (Davids 1973 ; Åbro 1979 ; Redmond and Hochberg 1981 ; Wohltmann 2000 ; Smith 2003 ; Shatrov and Felska 2017 ).…”

“…Feeding tubes of these taxa differ significantly. Trombiculid larvae, being parasites of vertebrates, produce relatively wide, always un-branched, and open-ended stylostomes (Voigt 1970 ; Wohltmann 2000 ; Shatrov 2009 ; Shatrov et al 2014 ). Most early-derivative water mite superfamilies have multiply-branched stylostomes (Eylaoidea, Hydrachnoidea, Hydryphantoidea), whereas later-derived ones (Hygrobatoidea, Arrenuroidea) have unbranched, closed-ended stylostomes (Smith 2003 ).…”