Certain plant substances in diet suppress genes that make ovaries, limiting the females who become queens:-http://www.the-scientist.com/?articles.view/articleNo/43864/title/Phytochemical-Helps-Differentiate-Workers-from-Queen-Bees/-"The result supports the idea that consumption of p-coumaric acid, along with other phenolic compounds found in honey and beebread, leads to “a form of chemical castration” of future worker bees, the authors wrote in their report. But p-coumaric acid is probably only part of the caste-determination story, Berenbaum added.-“'Royal jelly is important for producing queens,” she said, “but, apparently, plant products are important for producing workers.'”