Stylostome of Leptotrombidium myotis larvae (Ewing, 1929) (Acariformes, Trombiculidae) feeding on two different bat species (Vespertilionidae)

Larvae of Leptotrombidium myotis (Ewing, 1929) and their stylostome on the bats Plecotus ognevi Kishida, 1927 (Buryatia) and Myotis davidii (Peters, 1869) (Kazakhstan) were studied with scanning (SEM) and transmission (TEM) electron microscopy and histological methods. The stylostome of this trombiculid species in these two different host species was identically organized and is composed of the proximal eosinophilic cone, to which the larval chelicerae are cemented; the main hyaline-like, immunologically-inert unstained portion; and the distal azurophil region. The total length of the stylostome may reach 200 µm. Imaging by TEM shows that the stylostome is built of a homogeneous substance, which does not have any structurally different layers. The axial canal, around 10 µm in width, opens freely to the subjacent tissue and may contain different host cells and their debris. The skin inflammatory response to the parasites’ impact in these two host species appears to be different in its character and intensity. In P. ognevi, the epidermis is dissolved at the site of the larval penetration but peripherally, it undergoes hyperplasia. The inflammatory reaction is of moderate intensity with the presence of neutrophil leucocytes, macrophages and mast cells in the focus accompanied by dilation of the peripheral capillaries and edema. Conversely, in M. davidii, a strong reaction is observed with a total dissolution of the epidermis at the location of larval feeding, intensive hemorrhages in the dermis, and formation of a scab on the skin surface, formed of fused, necrotic inflammatory and epidermal cells that together contribute to the strong lesion in the skin. In this type of skin reaction, neutrophil leucocytes are predominant but mast cells are mostly lacking. Owing to this finding, it may be assumed that M. davidii from Kazakhstan has evolutionary evolved a strong resistance to feeding of this trombiculid species and may serve as a transitional agent of infecting pathogens.