Stylostome and feeding of the trombiculid larva Neotrombicula tianshana Shao et Wen, 1984 (Acariformes: Parasitengona) from the Baikal region

Abstract

Stylostome, skin reaction and feeding peculiarities of larvae of the trombiculid mite Neotrombicula tianshana Shao et Wen, 1984 were studied using histological, SEM and CLSM methods. Larvae of this species tend to attach and feed in tight groups inside ears, although single larvae may attach separately at sites with an unaffected epidermis. Correspondingly, every mode of stylostome formation may be observed. In any case, larvae produce relatively long stylostomes (up to 200 µm), which never extends beyond the epidermis (the epidermal stylostome type) irrespective of feeding site. In the mature condition, the stylostome shows a whitish homogeneous “hyaline-like” substance of its walls without conspicuous transverse or longitudinal layers. The stylostome character differs from that of other trombiculid larvae and mostly depends on the rate of saliva passage through the axial canal that, in turn, depends on the larval biology and feeding priorities. Feeding of this species leads to formation of a strong hypersensitive reaction caused, probably, by antigens in the larval saliva introduced by the larva through the stylostome into the wound. This cutaneous reaction is mediated by exudation of the neutrophile granulocytes and mononuclear lymphocytes through the walls of the extremely dilated terminal venules and capillaries and their migration to the attachment site. This process involves the sebaceous glands and results in the significant destruction of the epidermis and formation of scab on the skin surface that serve for elimination of the parasite from the host skin. Larvae uptake liquid nutrient substrate and never take up cell elements of the host. Nutrients are accumulated within the expanded midgut cells in the form of violet nutrition globules. If the larvae feed in a place with loosely organized destroyed epidermis, the stylostome may grow faster and relatively long stylosotomes may be associated with larvae in their initial feeding stages. Nevertheless, in all cases fully fed larvae always show totally developed stylostomes.

Keywords:

• feeding tube
• skin inflammatory reaction
• histology
• SEM
• CLSM
• Parasitengona
• trombiculid larvae

Acknowledgements

We wish to express our thanks to Dr. A.A. Stekolnikov (ZIN RAS) for his kind identification of the mite species and to Dr. A.A. Petrov (ZIN RAS) for his qualified assistance in the work with CLSM.

Additional information

Funding

This study is realized under the State Scientific Program [N 01201351187] and is also supported by a grant [N 15-04-01203-a] from the Russian Foundation for Fundamental Research and is performed on the instrumental basis of the Centre of Collective Use “TAXON” of Zoological Institute RAS.