Digestion in the tick,Argas persicus, Oken.

1.Studies on the histological changes during digestion in Argas persicus reveal that the ingestion of blood is accompanied by the destruction of the existing gut epithelial cells.2.The blood remains unlysed for 2–3 days while a new epithelium develops which contains cells that secrete a saliva-fast PAS-positive colloid that causes haemolysis.3.Other epithelial cells remove the freed erythrocytic nuclei by phagocytosis.4.Most of the gut cells then absorb protein from the lumen and intracellular digestion takes place leaving pure haematin granules as the waste product of the digestion of haemoglobin.5.After the initial rapid phase of digestion only relatively few cells show signs of absorptive and digestive activity.6.Absorption of protein is accompanied by increased alkaline phosphatase activity in the microvilli of the cell border; this activity is lost once absorption finishes and digestion begins.7.Strong aminopeptidase activity can be demonstrated at the border of some of the protein vacuoles.8.In vitro tests show that the gut proteinase is active only in the acid range with peaks at pH 2·6 and 3·8 and has a Km of 0·32 % with bovine serum albumin as substrate.9.In vivo data show that digestion, after haemolysis has occurred, takes place in two phases; the first is rapid and lasts approximately 1–2 weeks and is followed by the second phase which is slow and remains constant until the next blood feed.10.The proportion of the blood meal which remains after the rapid phase of digestion is determined by the sex and developmental stage of the tick and within each category it is constant and serves, in the absence of significant fat and glycogen reserves, as a food reserve.