The poplar leaf beetles Chrysomela tremulae and Chrysomela populi are the most important defoliating pests in both young plantations and short rotation stands of poplars in France. They damage poplars in the nurseries and plantations during the first three years of the establishment period. Larvae and adults feed on the most succulent leaves of young trees and reduce biomass production. They may also attack the bark, deforming the seedlings and the terminal shoots, or killing the young seedling. Insect feeding may also allow infection by pathogens and damage by secondary insects. The level of resistance was evaluated in progenies of intra- and interspecific crosses involving P. trichocarpa and P. deltoides, with the aim to determine the genetic basis of insect resistance, and to investigate relationships between phenolic compounds and resistance. P. deltoides parents were more resistant to chrysomelid beetles than P. trichocarpa. P. deltoides X P. deltoides progenies appeared more resistant than P. deltoides X P. trichocarpa crosses. In hybrid progenies, segregation was observed between heavily and weakly damaged clones. This work was carried out in the interspecific family on which the genome mapping is based, and further studies are under way to identify QTLs related to chrysomelid resistance. Phenolic glycosides, salicortin and tremulacin were quantified in the foliage of both species, but species-specific qualitative and quantitative variation of phenolic glycosides were observed. The role of phenolic glycosides in influencing insect resistance will be discussed.