Parthenogenesis, a phenomenon in which development occurs only from the egg nucleus without the involvement of sperm nuclei, has been reported in various animals. In the silkworm Bombyx mori, parthenogenesis can be artificially induced through various physical stimuli. Although extensive information exists for methods to produce the parthenogenetic individuals, detailed observations of nuclear behavior during the parthenogenetic processes are insufficient. This study focused on ameiotic parthenogenesis induced by hot water treatment at 46°C for 18 min and compared the nuclear behavior between parthenogenetic and fertilized eggs. In fertilized eggs, meiosis was completed within 6 h after egg laying at 15°C, and by 12 h, three mitotic divisions had been observed. In contrast, the first division of parthenogenetic egg nuclei required 6–12 h after treatment, resulting in a developmental delay of several hours compared with fertilized eggs. The nuclear behavior of parthenogenetic eggs is summarized as follows: (1) most of parthenogenetic eggs exhibited no division within 6 h post-treatment, (2) between 6 and 12 h post-treatment, ameiotic nuclear division occurred, with one nucleus migrating to the peripheral region of the anterior dorsal area and the other moving to the inner part of the egg, and (3) by 18 h post-treatment, the egg entered the syncytial nuclear division stage.

 The paper entitled “Non-directional pairing of the WZ chromosome bivalent in Bombyx mori” by Toshiaki Fujimoto, Susumu Katsuma and Ken Sahara that appeared in Journal of Insect Biotechnology and Sericology, Vol. 94, No. 2, pages 19 to 22, contains errors in the legend of Fig. 1 and in the text of Table 1 on page 21.