The environmental pollution, evolution of resistance, and risks to human and aquatic animal health associated with pesticide application have attracted much attention globally. Herein, we tested the capacity of diallyl trisulfide (DAT) from garlic essential oil to control the destructive stored-product pest, Sitotroga cerealella. The effects of DAT on the total content of cuticular chitin and structure of adults S. cerealella were evaluated. This study was the first to investigate changes in chitin structure in adults due to exposure to DAT through Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and differential scanning calorimetry. The results of these analyses revealed that the cuticular chitin content of pests decreased after DAT treatment. DAT treatment also reduced thermal stability and crystallinity of chitin. These findings indicate that DAT is a potent biopesticide that is active against the moth, and establishes the basis for its use as an IPM and alternative to chitin synthesis inhibitors.