Host—parasite relationships ofBlastocrithidia familiarisinLygaeus pandurusScop. (Hemiptera: Lygaeidae)

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Abstract
SUMMARY: Blastocrithidia familiariswere found to be parasitic in the midgut, ileum and rectum ofLygaeus pandurus. The host—parasite relationship is described. Attachment of parasites in the midgut and ileum occurs by interdigitation of expanded flagella over and between the microvilli. No attachment to microvilli was observed where extracellular membranes form well-organized layers which lie parallel to the gut wall and completely separate the microvilli border from the lumen. The extracellular membranes originate from delamination of the outer unit membrane of microvilli which consists of a double plasma membrane. The function of the extracellular membrane layers and their possible role as a peritrophic membrane in preventing parasite attachment is discussed in relation to previous studies on midgut cells in Hemiptera with a similar apical coat on midgut microvilli. In the rectum, parasites attach to the cuticle of the gland cells and not to the rest of the rectal wall. Attachment to the cuticle occurs by the formation of hemidesmosomes. A comparison of the relationship ofB. familiarisand its host to previous ultrastructural studies of associations between kinetoplastid flagellates and their respective hosts is discussed.