The structure of the male reproductive system of 5 species of Calaphidinae Clethrobius comes, Euceraphis betulae, Myzocallis (Lineomyzocallis) walshii, Tuberculatus (Tuberculoides) annulatus and Tuberculatus (Tuberculoides) neglectus is discussed. C. comes and E. betulae feed on birches (Betula), whereas M. (L.) walshii, T. (T.) annulatus, and T. (T.) neglectus are associated with oaks (Quercus). On the basis of histological sections and whole mount preparations the following elements in the structure of the male reproductive system have been examined: the number of testis follicles and the stage of spermatogenesis, the connection of follicles and vasa deferentia, the position of the proximal part of vasa deferentia as well as the development of accessory glands and the ejaculatory duct. In males of studied species the characters of the reproductive system have been observed: each testis holds 3 or 4 follicles, strongly elongated and arranged in a rosette. Vasa deferentia run separately along their length, only in the proximal part their walls cling together. Accessory glands are strongly elongated, sometimes asymmetric (T.(T.) annulatus) whereas the ejaculatory duct is usually reduced (in exception C. comes). These characters were then used to supplement morphological data in order to interpret developmental trends in the Calaphidinae.