New hybrids of the Shinese silkworm, Bombyx mori L. (Lepidoptera: Bombycidae) for industrial spring-time cultures - N. Petkov; J. Nacheva; P. Tsenov; V. A. Golovko; M. E. Braslaslavskij; A. Z. Zlotin (The Kharkov Entomological Society gazette)