ROYAL JELLY. “An early study also determined the cellular basis of the discrete caste morphology of A. mellifera. Queens arise when workers in a colony selectively feed chosen larvae royal jelly. The caste differentiation occurs through an epigenetic process; non-heritable factors contributing to gene expression. Queen and worker morphological forms both come occur from the same genome, royal jelly nourishment is the non-genetic determiner.”
http://en.m.wikipedia.org/wiki/Genetics_of_social_behavior