AbstractThe action of the chitin synthesis inhibitor, chlorfluazuron, was investigated in Spodoptera frugiperda wing imaginal discs cultured in vitro. Electron microscopy and cytochemical labeling with a lectin, wheat germ agglutinin (WGA), were used to monitor morphogenesis, as well as the presence and localization of chitin and non‐polymerized N‐acetyl‐D‐glucosamine (GlcNAc). Chlorfluazuron (CFA) selectively inhibited 20‐ hydroxyecdysone–stimulated chitin synthesis and procuticle deposition in imaginal discs, without otherwise affecting their morphogenesis. Tracheole migration, evagination, exocytosis, and endocytosis in the epithelial cells, and the presence of non‐polymerized GlcNAc in the extracellular matrix, were observed in both CFA‐treated and control wing discs. On the other hand, CFA prevented the appearance of WGA‐labeled chitin in newly formed procuticle, while the deposition of proteinaceous cuticulin and epicuticle was unaffected. A brief treatment with CFA resulted in WGA labeling of non‐polymerized GlcNAc, but not chitin in the procuticle region. The lack of chitin in CFA treated wing discs was correlated with the appearance of an amorphous, non‐lamellar procuticle region. © 1994 Wiley‐Liss, Inc.This article is a US Government work and, as such, is in the public domain in the United States of America.