The bark beetles colonization is a process perceived by their tree hosts as a biotic stress. The trees respond to this action by segregating oleoresin, which is toxic to these insects. It is known that cytochrome P450 monoxigenases are involved in some detoxification process in bark beetles. We are studying the expression of CYP genes in Dendroctonus valens because it has been demonstrated that host monoterpenoids (such as α-pinene) are toxic compounds; however, they are important for their chemical communication as well. To analyze the level expression of CYP genes, adult beetles were stimulated by 4, 8, 12 and 24 hours with α-pinene, R-(+)-α-pinene, S-(+)-α-pinene and S-(-)-β-pinene. After, mRNA from midgut, hindgut, foregut and antennae was extracted. RT-PCR was used to obtain the cDNA, which was amplified with specific primers for CYP4 and CYP6 genes. Both genes showed higher expression levels in the midgut from insects stimulated with S-(+)-α-pinene, but their expression were higher in the antennae with R-(+)-α-pinene and S-(-)-β-pinene. Expression levels were different depending on exposure time. On the other hand, the amplified fragments were cloned and sequenced to identify which CYP variants are expressed within each anatomical region of the beetle. The CYP6 fragment showed a high similarity (77%) with CYP6BJ1 from Leptinotarsa decemlineata and with CYP6K1 (71%) from Blattella germanica. CYP4 sequences corresponded to different variants (CYP4G27, CYP4BD1 and CYP4BGI) from Ips paraconfusus.