Abstract: Insecticide resistance occurs at three levels in insects: i) stopping penetration through barrier tissues ii) conjugation, storage, and metabolisation in internal tissues iii) modification of the molecular target site. The detection of these biological adaptations is often realized by the use of bioassays. This technique allows characterizing the resistance level of a population to a given compound, but is not informative on the mechanism. Therefore, it limits the potential of investigation and resistance management becomes more difficult. Molecular detection can be useful, enabling the identification of target mutations, and the modifications in the expression or the structure of detoxifying enzymes. Acetylcholine esterase and the sodium channel are two important molecular targets of organo-phosphosphates (OPs), carbamates and pyretroids, respectively. The study of gene sequences allows the development of molecular tools in order to screen field populations.We have already developed some molecular tools to detect pyrethroid resistance in Cydia pomonella. We are now investigating the molecular structure of target sites in other pest species, including Cydia molesta aiming to define new molecular tools for resistance detection. The first results are presented and discussed.