Unlikely to play an active role in the humoral immune defense. May have a function in the digestion of bacteria in the food. Hydrolysis of (1->4)-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. Found in the midgut. Maximal expression is found during the third larval instar, it drops to become undetectable in the late pupal stage. The expression in adults is similar to that of first and second larval instars. Belongs to the glycosyl hydrolase 22 family.