The foregut of Tribolium castaneum larva is divisible into pharynx and esophagus. Structurally the midgut is a simple tube without the projecting regenerative crypts, although in the adult the external surface of the midgut appears villous due to the presence of crypts. The large intestine is divided into pyloric, ileal and rectum chambers. In adult insects, the anterior intestine is divided into pharynx, esophagus and crop (Ameen and Rahman, 1973). The process of protein digestion in the red flour beetleis due to the presence of cysteine protease in the acidic anterior midgut and seine proteases, chymotrypsins, and trypsins in the alkaline posterior midgut. The importance of cysteine proteases in protein digestion, as well as the compartmentalization of these enzymes in the acidic anterior midgut, appears to be an adaptation in tenebrionid larvae to cereals containing abundant serine protease inhibitors. In fact, these coleoptera as part of an evolutionary struggle, adapt to protease inhibitors of plants and cereals to overcome the response of the plant to the attack of insects (Oppert et al., 2010). Under normal dietary conditions, T. castaneum larvae use primarily cysteine peptidases for protein digestion (Morris et al., 2009). The enzymology of the insect digestive tract in relation to initial stages of digestion of large food polymers (starch or protein) reflects the biochemical adaptation of these post-harvest insects to their preferred foods (Warchalewski et al., 2002).
The insects are characterized by feeding on stored grain, by increases of mold growth and excretion of compounds hydroxyquinone polluter that cause damage to the grain. For over 40 years, T. castaneum has demonstrated its ability to develop resistance to insecticides, in fact, resistant strains have spread geographically, so that it remains one of the major pests of stored products (Jones and Sattelle, 2007; Xu et al., 2009).