Midgut anatomy

Blood-sucking insects can be divided into two groups depending on the design of the alimentary canal for the storage of the blood meal. In one group, typified by Hemiptera and fleas, the alimentary canal is a simple tube with no diverticulae and the blood is stored in the midgut. In the second group, typified by Diptera, the gut has between one and three diverticulae which may be used, in addition to the midgut, for the storage of the blood meal (Fig. 6.1).

The midgut is the site of blood meal digestion and absorption. Two basic patterns of digestion are seen in blood-sucking insects: a batch system and a continuous system (Fig. 6.1). In the batch system, which is well illustrated by mosquitoes, sandflies and fleas, digestion proceeds almost simultaneously over the entire surface of the food bolus. The continuous system is typical of higher Diptera and Hemiptera, the blood meal being held in a specialized portion of the anterior midgut where no digestion takes place. Portions of the blood meal are then gradually passed down through the digestive and absorptive mid and posterior regions of the midgut. In this continuous system much of the meal will have been completely processed and defecated before some has even entered the digestive section of the midgut.

The blood meal is normally separated from the midgut epithelium by an extracellular layer known as the peritrophic matrix (previously known as the peritrophic membrane).