The B. mori yellow locus sequence was amplified from genomic DNA via PCR using specific primers designed from available genome sequences (Table S1). PCR was performed using KOD‐Plus‐Neo DNA polymerase (Toyobo, Tokyo, Japan) under the following conditions: 35 cycles at 94 °C for 2 min, 98 °C for 10 s and 68 °C for 30 s/kb. PCR products were subcloned into a pTA2 vector (TArget CloneTM, Toyobo, Tokyo, Japan) and sequenced with an ABI3130xl genetic analyser (Applied Biosystems, Foster City, CA, USA). The DNA fragments of yellow used for reporter constructs were cloned into the vector pBacGFP‐3xP3DsRed (Tsubota et al., 2014). For the reporter assay, the native yellow promoter, initiator, and TATA were used (Fig. S1). We confirmed that this 1.2‐kb genomic region lacks GFP reporter expression (Fig. S2).