Biological invasions represent an eminent problem for both conservation and agriculture/silviculture. Insects (Insecta) comprise a large proportion of important invasive pests. Information on the ecology of invasive insect species in novel environments is crucial for efficient control, prevention and damage mitigation. The main aims of this dissertation thesis were: 1) to evaluate the influence of select environmental factors on the distribution and abundance of the black timber bark beetle (Xylosandrus germanus Blandford) and 2) to assess the vertical distribution and temporal dynamics of larval feeding of the box tree moth (Cydalima perspectalis Walker) on host plants. Our results show that the distribution and abudance of X. germanus is significantly influenced by altitude, while forest stand/habitat type did not have a significant effect. Furthermore, we determined that X. germanus is expanding vertically into altitudes of up to 1000 m a.s.l. and that it is univoltine in the Western Carpathians. After comparing abundances of this species before and after a harsh winter (2016/2017), we assume that low winter temperature will not stop its further spread. Research on C. perspectalis has shown that the distribution of larvae and leaf damage is non-uniform within host plants. Both are significantly affected by height level (height of branches above ground). Leaf damage is greatest in the lower height levels, eventually moving into higher levels until complete defoliation of the host. The results of this work will be applicable in forestry and horticultural practices, especially in monitoring and control of both species of invasive pests.