Chitin is an important structural component of the cuticle and peritrophic matrix of insects. The red flour beetle, Tribolium castaneum, has multiple isoforms of chitin synthases and chitinases, which synthesize and degrade chitin, respectively. To determine the role of individual isoforms of these enzymes in chitin metabolism, we have utilized RNAi-mediated gene knockout experiments using larvae, prepupae and pupae of this beetle. The effects of injections of isoform-specific dsRNA on the phenotype, levels of specific transcripts, morphology, development, and chitin content of insects were determined. These experiments reveal the biological roles of some of the isoforms of chitin synthases and chitinases (Supported in part by National Science Foundation).