Silkworms were fed either mulberry leaves or an artificial diet (Nihon Kosan Kogyo, Yokohama, Japan) and maintained under a 12 h light/12 h dark photoperiod at 25–27 °C as previously described (Tsubota et al., 2014). Both nondiapausing (w1‐pnd) and diapausing (w‐1) silkworm strains were used in this study. Silkworms were kept at the Transgenic Silkworm Research Unit of the Division of Biotechnology at the Institute of Agrobiological Sciences, National Agriculture and Food Research Organization, Tsukuba, Ibaraki, Japan. The chk12 mutant strains were provided by the Silkworm Stock Center, located at Kyushu University, and supported by the National BioResource Project.