A cDNA clone corresponding to an mRNA which accumulated in the wing disc ofBombyx morihas been characterized. The accumulation was restricted to the feeding periods of the intermolts, and the mRNA rapidly disappeared during the larval molt and the spinning period. This accumulation was strongly inhibited by 20-hydroxyecdysone bothin vivoandin vitro.The amino acid sequence predicted for the putative protein corresponds to that of theBombyx moristorage protein 1 (Sakurai et al., 1988). Usingin situhybridization, the mRNA was located in cells associated with trachea formation. Significance of the presence of the mRNA of a storage protein in developing wing disc is discussed.