Hydrolyzes the N-acetamido groups of N-acetyl-D-glucosamine residues in chitin. [(1->4)-N-acetyl-beta-D-glucosaminyl](n) + n H2O = n acetate + chitosan Expressed in midgut where it is found in the peritrophic membrane, a semi-permeable acellular matrix which lines the digestive tract (at protein level) (PubMed:24473143, PubMed:30987273). Not detected in foregut or hindgut (at protein level) (PubMed:24473143). Highly expressed in newly emerged larvae at second, third, fourth and fifth instar stages (PubMed:24473143, PubMed:30987273). Has lower expression during the molting phases of larval development (PubMed:24473143, PubMed:30987273). No expression detected during pupal stages (PubMed:24473143, PubMed:30987273). Up-regulated in response to 20-hydroxyecdysone (20E) and juvenile hormone analog. Belongs to the carbohydrate esterase 4 (CE4) family.