Bees Can Smell How Much Sex Their Queen Has Had

Just because girl talk between bees is wordless doesn't mean it lacks for intimate details. When sister honey bees gather around their queen, they can tell from her pheromones whether she's mated—and how much. What they learn may determine whether they let her live.

The queen honey bee doesn't do much day-to-day ruling, but she does lay nearly every egg in the hive. Her daughters become worker bees, who keep the colony running. Pheromones that the queen and the workers emit—then spread through the hive as they touch antennae and clamber over each other's bodies—carry the signals that maintain order. Among other laws, the queen's pheromones tell workers not to lay eggs of their own.

When the queen's egg-laying prowess starts to fade, though, her workers will replace her without sentimentality. They prepare special queen egg chambers and feed royal jelly to the chosen larvae (who will battle once they emerge, leaving only one queen standing). Then the workers sting the old queen to death. "It can take up to 6 weeks for the new queen to produce a new cohort of workers," says Elina Niño, an entomologist at Pennsylvania State University. So the process harms the hive's productivity, in addition to the dispatched queen herself.

Along with colleagues at North Carolina State University (where she worked at the time) and Tel Aviv University, Niño investigated whether the queen honey bee is honest when she sends pheromone messages to her workers. If the queen could fake the pheromones that say she's in great shape, it would keep her colony loyal for longer. To find the answer, the researchers set about artificially inseminating some bees.

New queens mate just once in their lives, in a sex spree that involves lots of males (called drones). They store all that sperm and use it, a little bit at a time, to fertilize the eggs they lay for their remaining years. The scientists gathered groups of queen bees who had not yet mated with any drones. Then they simulated sex in several ways: Some queens had a needle inserted into them to mimic the physical aspect of mating. Some received actual semen (mixed from the contributions of multiple bachelor bees), in either a large or small volume. Others were pumped with a large or small volume of salt water.

Several days later, the unfortunate queens were offed. The researchers extracted the contents of two pheromone glands, one at a queen bee's mouth and the other near her stinger. Chemical analysis showed that in the pheromones from the bees' back ends, there was a difference between queens who'd been inseminated (or faux-inseminated) and those whose insides were still empty. The pheromones from the jaw gland seemed to carry even more specific information: each group of queens (inseminated for real or with salt water, holding a large or a small volume of whatever it was) had a distinct chemical signature.

But how would worker bees respond to these signals? The scientists put their pheromone extracts onto glass plates and set them down by groups of worker bees. They hoped to take advantage of a bee behavior called the "retinue," in which workers cluster around a queen while licking her and touching her with their antennae.

The worker bees treated the pheromone puddles like real queens. But not all queens were equal. The researchers saw that workers were most attracted to pheromones from queens who were full of semen, rather than salt water. They also preferred pheromones from queens with a larger volume of semen stuffed inside of them.

"Colonies headed by multiply mated queens are more productive, more resistant to diseases and more likely to overwinter successfully," Niño says. In other words, queens that have mated with lots of drones produce hives that are healthier, because they're more genetically diverse. So it would benefit worker bees to be able to sniff out their queen's sexual history and "act accordingly," Niño says. This might mean ousting a queen who hasn't gotten around much, and gambling on a new queen instead.

For beekeepers, the results add new importance to having a healthy queen. Just because a queen is laying eggs, Niño points out, doesn't mean she can keep her subjects loyal. Workers that don't like the smell of their queen's pheromones, perhaps because she hasn't mated with an adequate number of drones, may execute her. Beekeepers who want to avoid that drama should make sure their queen has plenty of partners—because when she talks to her workers about her sexual past, she won't be able to lie.

Image: by Dude-K (via Flickr)

Niño EL, Malka O, Hefetz A, Tarpy DR, & Grozinger CM (2013). Chemical Profiles of Two Pheromone Glands Are Differentially Regulated by Distinct Mating Factors in Honey Bee Queens (Apis mellifera L.). PloS one, 8 (11) PMID: 24236028

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