Doublesex-mab3-related transcription factor (DMRT) genes encode a family of transcription factors that are conserved among phyla. DMRTs are related to sex determination or differentiation. However, several DMRTs, known as DMRTAs, are irrelevant to sex determination and sexual differentiation, but play an important role in neurogenesis in diverse animal species. In this study, we identified a Bombyx ortholog of an arthropod-specific DMRT, dmrt99B (designated Bmdmrt99B), and characterized its function. Bmdmrt99B was preferentially expressed in the ovary and brain of larvae. The food-seeking ability of the larvae of two Bmdmrt99B mutant strains was disrupted, which decreased their food intake. The Bmdmrt99B mutant larvae also showed abnormal scattering behavior. Moreover, mutant adult males responded to the female sex pheromone but could not localize its source. Our findings suggest that the neurogenetic function of DMRT is conserved among insect species and that DMRT plays an important role in the regulation of normal behaviors in insects.