Increasing areas of gradation, making it difficult or impossible to perform restorations and forestations, and as causing tree crown damage, result in the need to intensify monitoring of beetle populations. In order to support control activities, the study assessed the species structure, morphological traits and genetic variation in Melolontha spp. from five pine stands with different composition and proportion of admixed tree species. The study applied ISSR and COI methods and identified minor variabilities between the analyzed populations, which may be the effect of high gene flow and absence of complete geographic isolation. Our research indicated high population dynamics and the degree of its migration, as evidenced by the gene flow rate. Given the rapid spreading potential, current methods of countering pest expansion are rather ineffective. The species, morphological and genetic structures were found to be associated with the area of beetles’ occurrence, which may depend on the proportion and composition of admixed tree species, which beetles use for supplementary and reference feed- ing. This species showed higher values of the genetic variation parameter in areas dominated by M. hippocastani compared to M. melolontha. However, the opposite situation was observed in the area with M. melolontha dominance.