Among the
several Papilio species, interspecific hybrids have been obtained using hand-pairing technique (Clarke and Sheppard 1953, 1956; Ae 1995). We therefore compared species-specific mRNA expression in an F1 hybrid specimen. The hybrid experiment showed that the difference in YRG expression is caused mainly by changes in trans-regulation between P. xuthus and P. polytes. Our findings shed light on the gene-regulatory networks for larval color pattern in Lepidoptera.