Originally used for landscaping, the Ailanthus altissima (Mill.) Swingle) has become an invasive species requiring biocontrol, with the Aculus taihangensis mite as one of its potential agents. Given this, research aimed to determine the species composition of herbivorous mites on A. altissima trees in the Botanical Gardens of Kyiv and Zhytomyr and identify the peculiarities of their distribution and development. To achieve this goal, leaf samples were collected from A. altissima plants, with further identification of the detected mites according to the methods accepted in acarology. As a result of the monitoring, the alien mite A. taihangensis of the superfamily Eriophyoidea was detected on A. altissima plants for the first time in Ukraine, namely in the Fomin Botanical Garden of the National Academy of Sciences of Ukraine and the Botanical Garden of Polissya National University. It was found that more intensive reproduction of this phytophage occurs on female plant specimens compared to male ones. The mites preferentially colonise and reproduce more intensively on the leaves of the lower part of the crown, where the air humidity is much higher than in the upper part. These data are important for estimating the number of A. taihangensis populations to optimise sampling. It was found that the intensity of mite reproduction during the growing season of host plants gradually increases. Thus, the intensity of reproduction of the first generation of mites was low (0.14-0.70 times), while for the next generation of phytophagous mites, this index increased and reached 0.97-1.3. The comparison of morphological measurements of A. taihangensis collected in different ecological and geographical zones confirmed the high variability of individual characteristics in the new habitat. Three groups of traits were identified according to the level of variability: high, moderate, and low variability. Results add to the knowledge about the diversity of eriophyoid mites in Ukraine and their impact on A. altissima
eriophyoid mites, bioagent, invasion, morphological variability, phytophag, tree crown