Phd Thesis 33 - eCommons@USASK - University of Saskatchewan

1. GENERAL INTRODUCTION
1.1 The Insect Gut
In nature, insects exploit a wide diversity of food sources. Although these differences in
feeding habits lead to significant variability in gut structure and function, the insect gut is in
almost all species a continuous tube throughout the body and primarily divided into three
regions; the foregut (stomodeum), the midgut (mesenteron) and the hindgut (proctodeum)
(Gillott, 2005) (Figure 1.1). The foregut’s main roles are ingestion, storage, grinding and
transportation of food to the midgut. The midgut is the principal site for secretion of digestive
enzymes and for digestion and absorption of digested products. The hindgut regulates the
absorption of water and salts from waste products in the alimentary canal.
Insects protect themselves against various harmful biotic and abiotic factors in the
environment by their cuticular integument (Wang and Granados, 2001). The foregut and the
hindgut are also lined with a protective cuticular layer called the intima; however, the midgut
lacks this layer. Instead, epithelial cells at the foregut midgut junction or along the entire midgut
produce a semipermeable, sheath-like, acellular structure called the peritrophic matrix (PM)
which surrounds the food bolus. The PM separates the midgut into two regions; the
endoperitrophic space which contains the food bolus, and the ectoperitrophic space which is the
region between the PM and the midgut epithelium (Figure 1.1). The PM may also line the
hindgut and is later eliminated with the fecal pellets (Brandt et al., 1978).
Figure 1.1 The alimentary canal of a lepidopteran larva. (Source: Sarauer, 2002).
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