The paper deals with the occurrence, development and harmfulness of imported willow leaf beetle (Plagiodera versicolora Laich.) in riparian and accompanying stands of the Svratka and Svitava rivers in the region of Brno. Salix fragilis L. and S. × rubens Schr. are the most damaged species there. Imagoes leave wintering places usually at the beginning of May. During about a 60-day period, they damage ca. 23.3 cm² leaves of S. fragilis and lay 250 to 730 (on average 539) eggs. The whole egg-laying consists of 16 to 48 (on average 35.5) groups with 6 to 26 (on average 15.2) eggs. The fecundity of females hatched in the laboratory is minimally twice lower. Larvae hatch after 5 to 8 (in the laboratory after 4.3) days and damage about 282 mm² leaves. The development from laying eggs until hatching imagoes of the
1^st generation takes about 21 (in the laboratory about 15) days. Imagoes of the 1^st generation occur on trees from the end of May to mid-August and die after completing their reproduction. Plagiodera versicolora creates 3 to 4 (in the laboratory 4 to 6) generations during a year. The small part of imagoes of the 2^nd generation, predominant part (or all) imagoes of the 3^rd generation and under conditions of a tetravoltine development all imagoes of the 4^th generation enter a diapause. In the course of the growing season, the food consumption of imagoes and larvae decreases and fecundity of females markedly decreases. Schizonotus sieboldi (Ratz.), Medina melania (Meig.) and M. luctuosa (Meig.) rank among main enemies of Plagiodera versicolora.