An invasive species of an aggressive plant pest, the emerald ash borer (EAB), Agrilus planipennis Fairmaire (=A. feretriue Obenberger, A. marcopoli Obenberger), was found and identified in Moscow ash trees for the first time in 2005. The widespread withering of Moscow ashes had been registering since 2004 and EAB was considered to be the main reason for this process. A short description of the insect structure, biology, and usual ranges of distribution is presented. The Palaearctic Oobius zahaikevitshi Trjapitzin [Tryapitsyn, 1989], which parasitizes in the eggs of narrow-body borers, may be considered as an available species for EAB pest control. It seems likely that the EAB was brought in at the beginning of the 1990s with planting material from North America. Transport of the insects with wooden tare from China directly could be another possible path of the invasion. The species should be viewed as a quarantine one.