Morphological studies on the extracellular structure of the midgut of a tick, Haemaphysalis longicornis (Acari: Ixodidae)

In the present study, morphological observations on the extracellular structures found on the apical surface of the midgut epithelium, known as the peritrophic membrane (PM) or glycocalyx, are described in Haemaphysalis longicornis females and larvae. These structures have been hypothesized to provide protection to the microvilli of epithelial cells of the digestive tract. Our aim was to determine whether the extracellular structures are important in the digestion of the blood meal and/or as a protection against infection or injury. The PM was detectable in the midgut of engorged larvae by electron microscopy, but not in engorged females. However, a PM-like structure, stainable with toluidine blue, was observed in females by light microscopy. From the results of confocal laser scanning and electron microscopic observations with wheat germ agglutinin (WGA lectin) staining for chitin of the PM, however, the structure was clearly recognized. The structure in the female is likely to be PM because staining with WGA lectin in the presence of GlcNAc indicates the presence of chitin and various morphologies of PM have been reported in insects and ticks. These results show morphologically that different types of PM-like structure are formed in larvae and females of H. longicornis.