Role of Microorganisms in Digestion and Nutrition

Microorganisms play several roles in insects. However, in this chapter, we will consider only the roles of microbiota in insect digestion and nutrition. Bacteria are food for insects, exemplified by larval houseflies and blowflies, living in feces, decaying fruits, and corpses that are rich in bacteria. Microbiota, particularly bacteria, also play a role in the digestion of recalcitrant materials such as tannins, lignins, and humic substances. The last ones are complex molecules derived from residues occurring in soils. Bacterial action on those recalcitrant molecules is observed in termites and some beetles. Fungi are important players in lignocellulose digestion in termites of the subfamily Macrotermitinae. Sap-feeding insects usually lack essential nutrients, especially amino acids, which are supplied by microbial symbionts, such as those found in pea aphids. In diets poor in vitamins, symbiont microbiota may provide them for the insect, exemplified by the blood-feeder Rhodnius prolixus. Finally, gut microbiota help their hosts in detoxifying molecules that are characteristic of plant defenses or insecticides used in insect control.