Pseudococcus comstocki (Kuwana) is a polyphagous mealybug native to Asia. It is a pest of ornamentals and fruit trees (apple, pear and peach) in America and eastern Europe where this species has been incidentally introduced. It was first recorded in western Europe (Italy and France) in 2004. In summer 2006, additional foci of this mealybug were discovered in northeastern Italy on ornamental plants and in peach orchards. Its phenology and distribution have been investigated in northeastern Italy. P. comstocki develops three generations per year and overwinters in the egg stage. Overwintered eggs hatch from April onward and crawlers infest leaves and apple and pear flowers. The adult females of the three generations were observed in June (1st generation), late July-August (2nd generation), and from late September to November (3rd generation). Most of adult females move from leaves to old branches and the trunk to lay eggs. In infested orchards females are often concealed in the fruit calyx (on pears and apples) or at the fruit stem cavity (on peaches) and after fruit picking are transported far away by fruit trading. Indirect damage, i.e. honeydew excretion and development of sooty mould is remarkable, leading to early defoliation and fruit quality deterioration. Monitoring carried out on mulberry trees and ornamentals over an area of 150 km2 in the Veneto Region demonstrates that these plants can act as permanent foci of this species in the territory.