The insects of genus Dendroctonus are pine parasite beetles that interact chemically with their host. These insects colonize the tree through visual and olfactory signals, as part of their live cycle. The trees respond to this attack, secreting an oleoresin, which is a mixture of compounds named monoterpenes, mainly á-pinene and myrcene. These compounds are toxic for the insects; however, the beetles are able to transform them in more soluble and less toxic molecules. It has been reported that the cytochrome P450 complex and Glutathione-S-Transferase (GST) are involved in detoxification processes. The P450 complex consists in four gene families (cyp2, cyp3, cyp4 and a mitochondrial cyp12). Here we reported the localization of their corresponding proteins in midgut epithelial cells from Dendroctonus valens. The midgut region from adults was processed for transmission electron microscopy, as well as for confocal microscopy. Then, an immunehistochemestry assay for localization of P450 proteins was performed. We tested the next antibodies in both microscopy techniques: anti-rabbit CYP4A1and anti-calnexin as molecular marker of endoplasmic reticulum. As overlapping of both labels showed, the CYP4A1 was localized in endoplasmic reticulum (ER). These results suggest that the P450 complex is involved in the detoxification process, since previous work showed that the ER is overexpressed when insects are stimulated with monoterpenes.