May be involved in chitin synthesis in the pharynx during larval development. [(1->4)-N-acetyl-beta-D-glucosaminyl](n) + UDP-N-acetyl-alpha-D-glucosamine = [(1->4)-N-acetyl-beta-D-glucosaminyl](n+1) + H(+) + UDP Specifically expressed just prior to each larval molt (PubMed:11589574). Expression is restricted to the pharynx and specifically to the glandular cells g1 and g2 in the terminal bulb, the 3 m4 myo-epithelial cells in the metacorpus and the 3 m3 myo-epithelial cells in the procorpus (PubMed:16098962, PubMed:11589574). Not expressed in adults (PubMed:11589574). RNAi-mediated knockdown causes a severe delay in larval development with most animals arrested at the L1 larval stage (PubMed:16098962, PubMed:15777697). Arrested larvae have a disorganized and larger pharynx grinder probably causing feeding defects and thus a delayed growth (PubMed:16098962). Belongs to the chitin synthase family. Class IV subfamily.