Why Worker Bees Don’t Have Babies

Honeybees are great. They’re important pollinators, industrious honey-makers, and they’re darn cute (just look at that fuzzy body!). But you don’t get to be as successful as they are without making some brutal choices. Those efficient, humming colonies of theirs are ruled by rigid, hierarchical laws that determine who can eat, who can leave, and who can reproduce. Exactly how those laws were enforced has long been a subject of great interest to scientists, and now one team of researchers say they’ve figured out how exactly the queen keeps her workers’ fertility in check. They published their findings in the journal Nature Communications. 

An individual bee’s behavior (bee-havior?) is subject to all kinds of influences, whether it be the waggle dance of a returning forager, the electrical messages put out by a flower, or the many chemical signals drifting through hive air. One notable signal is queen mandibular pheromone, or QMP. QMP is an astonishingly versatile compound. It tells drone bees when the queen is ready to mate, induces the colony to swarm, and can destroy the ovaries of worker bees to keep them from getting busy. Pretty impressive, right? 

Previous studies in fruit flies had found a link between the flies’ egg production and a cellular pathway called the Notch. To find out if the same pathway had any involvement in honeybees' egg shutdown, evolutionary biologists at New Zealand’s University of Otago treated some workers with a chemical that suppressed any Notch activity and left other workers’ Notch signaling intact. Then all the bees were exposed to typical levels of QMP. The researchers killed the bees, then examined their ovaries to see what had happened.

Sure enough, the ovaries of bees with normal Notch function were damaged by the QMP. But before their deaths, the blocked-Notch bees had been humming along just fine; many of their ovaries contained fully developed eggs.

Additional tests on the bees confirmed a strong bond between Notch and QMP. When worker bees were left to their own devices and not exposed to a queen or her pheromones, their Notch receptors gradually degenerated. Without a queen, the workers' fertility was unfettered.

The researchers were surprised to see just how early in the reproductive process Notch could make a difference. Speaking in a press statement, co-author Peter Dearden said they’re still not sure if the pheromone attacks the ovary directly or works through the brain.

"However it is acting, the outcome is that Notch signaling's fundamental role in the ovary has been modified and transformed in honeybees into social control of worker bees' reproduction," he said.

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