CHITIN SYNTHESIS IN SPODOPTERA-FRUGIPERDA WING IMAGINAL DISKS .2. SELECTIVE ACTION OF CHLORFLUAZURON ON WHEAT-GERM-AGGLUTININ BINDING AND CUTICLE ULTRASTRUCTURE

The action of the chitin synthesis inhibitor, chlorfluazuron, was inve stigated in Spodoptera frugiperda wing imaginal discs cultured in vitr o. 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. Tr acheole migration, evagination, exocytosis, and endocytosis in the epi thelial cells, and the presence of non-polymerized GlcNAc in the extra cellular matrix, were observed in both CFA-treated and control wing di scs. On the other hand, CFA prevented the appearance of WGA-labeled ch itin in newly formed procuticle, while the deposition oi proteinaceous cuticulin and epicuticle was unaffected. A brief treatment with CFA r esulted in WGA labeling of non-polymerized GlcNAc, but not chitin in t he procuticle region. The lack of chitin in CFA treated wing discs was correlated with the appearance of an amorphous, non-lamellar procutic le region. (C) 1994 Wiley-Liss, Inc.