Factors contributing to the seasonal occurrence of the willow leaf beetle Plagiodera versicolora

We conducted a 3‐year study of a natural population of the willow leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae) on a river bank of the Inukami River, Shiga, central Japan, where four willow species ( Salix chaenomeloides , S. eriocarpa , S. integra , and S. serissaefolia ) occur sympatrically. Our survey showed that: (1) at the study site, the abundance of P. versicolora greatly varied among years and among willow species; (2) adult abundance changed seasonally with species‐specific patterns on different willow species; and (3) the dispersal‐settlement of adults had the most pronounced effects on the seasonal population growth rate of P. versicolora . Factors affecting these results were discussed.