The queen controls reproduction in the hive, and through that action she exerts a lot of pressure on what the workers decide to do, but she does not make the day-to-day decisions of the workers. Their behavior is influenced by the concurrent decisions of nest mates as well as by the impact of the environment outside the nest.
Queen substance is a pheromone, from the Greek phero, meaning "to bear," and hormone. Pheromones are chemical bouquets that trigger natural, behavioral responses in other individuals of the same species. Queen substance, also known as queen mandibular pheromone (QMP), is produced by the mandibular glands in the head of the queen honey bee once she has mated and is laying eggs. QMP is one of many compounds used for chemical communication within the colony. Workers smell the queen substance when they lick her body in the course of attending to her needs, and it gets passed around the colony as the bees touch each other. Because her pheromone is unique and distinct within the colony, it helps keep the colony integrated and centered around the queen as long as she is reproductively viable and the colony is healthy.
Among other effects, QMP suppresses the development of the workers' ovaries and inhibits them from rearing new queens. It signals to them, in combination with a chemical marker the queen deposits on her eggs and the presence of an adequate number of larvae, that the queen's egg laying and brood development is going well, and it influences the workers to exercise reproductive self-restraint. In the European honey bee colonies that they studied, Madeleine Beekman and Benjamin Oldroyd found that approximately 1 percent of the workers had active ovaries and were able to lay eggs. Somehow their ovaries had become activated despite all the cues to the contrary, but if they actually produced eggs, the eggs would most likely be removed, destroyed, or eaten by other workers because they lacked the queen's mark.
Christina Grozinger and her collaborators working on the Honey Bee Genome Project studied the role of QMP on gene expression, and they determined that exposure to QMP leads to direct changes in gene expression in the brains of honey bee workers. They reported that QMP consistently activates a group of genes that regulate nursing behavior and represses the activity of genes that regulate foraging activity, suggesting that QMP may delay behavioral maturation (from nurse to forager) by its effect on these groups of genes. In related research, Vanina Vergoz and colleagues identified a queen mandibular pheromone that prevents young bees from learning when to sting and has the effect of keeping them in close contact with their queen.
When the bees are about three weeks old and have become mature enough to leave the hive and begin foraging, the pheromone wears off and they learn how to defend themselves. This pioneering area of research will undoubtedly lead to additional discoveries about pheromonal control of behavior in bees. As the queen ages, her pheromone production starts to flag, her egg laying slows down, and she begins to lose reproductive control of the hive. If the queen dies or is removed from the colony, her absence is quickly noted and the behavior of the workers changes rapidly. When queen substance is scarce or is missing from a colony, the workers know that it is time to start constructing queen cells in order to rear another queen as a replacement.
There is one area where new research has established that the queen does not control the hive, as was previously thought. Andres Pierce and Lee Lewis, working with Stanley Schneider at the University of North Carolina at Charlotte, observed that colony reproduction, which involves the process of swarming and supercedure (replacing the queen), is regulated mainly by older workers rather than by the queen. In their words, the queen is relegated to the role of "passive egg layer whose own behavior is programmed, with changes dictated by signals delivered by older workers" in the form of piping and vibration signals. During the two- to three-week period before swarming, older workers signal to the queen and the rest of the colony that it is time to swarm. With the queen in a passive role, they come to a group decision on a new place to locate the nest, and then they arouse the queen and the bees in the swarm and lead them all to their new home, where the queen resumes her reproductive responsibilities.
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