Experimental evidences have demonstrated that α-pinene is a toxic compound for bark beetles. It has been found that the epithelial cells of the midgut from Dendroctonus jeffreyi, and Ips pini are involved in pheromone production, and probably in detoxification process. D. valens is not an aggressive killer of tree species, and no pheromone has been identified so far. In this study we documented the ultrastructural changes in the midgut epithelial cells of Dendroctonus valens induced by α-pinene, and the presence of P450 complex in these cells. The untreated midgut was constituted by the typical epithelia, the cytoplasm was granular and spongy, the nucleus was large, ovoid-shaped, with one or several nucleoli, and located in the center of the cell, primary lysosomes were scarce and mitochondria were found throughout the cytoplasm, with normal crests, the rough endoplasmic reticulum and free ribosomes were widely distributed; it was common to observe empty vacuoles and secretion vesicles irregularly scattered in the cytoplasm. In the treated midgut, the amount of secondary lysosomes, and mitochondria increased, the mitochondrial crests were affected, the rough endoplasmic reticulum were abundant, with the presence of secretion vesicles with electron-dense granules, and evident Golgi complex. Additionally, by immunochemistry assay we found activity of P450 complex in the anterior midgut after the application of α-pinene.