Discovered! A specific phytochemical in beebread is what makes a worker bee a worker bee and not a queen
There are two genders of honey bees in a hive, but 3 distinct castes: male bees (drones) and female bees (workers and queens). The difference between workers and queens are physiological. You can think of queens as "fully realized" female honey bees. They have functioning ovaries, for example, whereas workers do not. Honey bee workers are sterile. They have hormonal differences and pheromonal differences.
Male bees are produced from unfertilized eggs. An unfertilized egg will always
produce a drone.
Female bees, both workers and queens, all start off the same. Female bees are born of fertilized
eggs. And for 3 days after that egg hatches, the life of that female bee-to-be ... is indeterminate. That larva can become a worker, or that larva can become a queen.
After day 3... the worker bees within the hive who are on rotation serving as caretakers of the brood (nurse bees) make a determination whether that female larva will become a worker or a queen. After the determination is made, the nurse bees control the process with the diet of baby food supplied to the larva.
We have known for a very long time that queen bees are fed royal jelly (a glandularly produced food) for largely their whole lives and that worker bees are at first fed royal jelly (those first 3 days) and then a mix of royal jelly and "bee bread" (a processed pollen mixture) for the remainder of that young bee's larval stage. But we didn't know what the factor in stunting the larva's growth was. We didn't know until ... just now.
Check out the summary article, "Beyond royal jelly: Study identifies plant chemical that determines a honey bee's caste".
 What the study illustrates is that beebread contains an organic plant compound called p-coumaric acid
that comes from the pollen in the diet. This compound when ingested causes certain genes to be expressed and other genes to be suppressed. Feed female larvae beebread from day 4 onward and you get a worker honey bee as a result.
Fascinating. We have known for some time what was going on at a fairly high level (which is a feat in itself) but now we can see how the symbiotic relationship of honey bees with the world of plants has an effect at the genetic level that the honey bees "know" how to leverage to maintain the structure and order of their hives. Just amazing. Kudos to the University of Illinois-based researchers.
 There is much speculation about how this happens.
 Article: http://phys.org/news/2015-08-royal-jelly-chemical-honey-bee.html
 Research paper: http://advances.sciencemag.org/content/1/7/e1500795.full