Gene silencing through the introduction of double-stranded RNA (RNA interference, RNAi) provides a powerful tool for the elucidation of gene function in many systems, including those where genomics and proteomics are incomplete. The use of RNAi technology for gene silencing in Lepidoptera has lacked significant attention compared to other systems. To demonstrate that RNAi can be utilized in the lepidopteran, Plodia interpunctella, we cloned a cDNA for tryptophan oxygenase, and showed that silencing of tryptophan oxygenase through RNAi during embryonic development resulted in loss of eye-color pigmentation. The complete amino acid sequence of Plodia tryptophan oxygenase can be accessed through NCBI Protein Database.