Queen bees mate with dozens more males than previously thought and some of these drones father more appealing future queens, according to entomologists at North Carolina State University.

Despite humans' close relationship with honey bees for thousands of years, our knowledge of their behaviour and genetics is still patchy.

Textbooks from the Victorian era to the 1970s told us a queen bee mates with only a single drone, but in the past few decades that number has gradually been creeping up.

PhD student James Withrow from North Carolina State University has been investigating this behaviour — known as hyper-polyandry — by analysing the genetics of bee larvae as well as workers and queens, in a paper published in PLoS ONE today.

He said previously, most genetic research only sampled the genes of worker bees and concluded that most bees in a single hive were descended from around 12 different males.

But this new study looking at larvae too suggests researchers may have been missing many rarer "royal families" that develop into queens but may not mature into workers.

By sampling more of the larvae, researchers are now finding that in one hive, bees may have up to 50 different fathers.

"It seems like we have just been missing a lot of these in the traditional sampling," he said.

Bees gettin' busy

Drone pupae in the hive. ( Wikimedia Commons )

Bee-mating events can involve several thousand drones all gathering in areas about 20 metres above the ground in open fields, according to University of Sydney behavioural geneticist Benjamin Oldroyd.

Once mature, a young queen bee will leave her mother's hive and may visit several different "drone congregation areas" on different days, possibly mating with about 50 drones.

What's the buzz on all these bees? There are three types of bee in each hive: queens, workers and drones. Queens and worker bees are female and are made from fertilised eggs, so they receive genes from both the queen and a drone from another hive

Queens and worker bees are female and are made from fertilised eggs, so they receive genes from both the queen and a drone from another hive Workers do not sexually mature and so cannot breed but have important roles in maintaining and building the hive, feeding larvae and foraging for pollen

Workers do not sexually mature and so cannot breed but have important roles in maintaining and building the hive, feeding larvae and foraging for pollen Queens begin life similar to workers but, while workers switch from being fed a diet of royal jelly to a mixture of nectar and pollen, queens continue to be exclusively fed the protein- and sugar-dense jelly and so become sexually mature and much larger than other bees

Queens begin life similar to workers but, while workers switch from being fed a diet of royal jelly to a mixture of nectar and pollen, queens continue to be exclusively fed the protein- and sugar-dense jelly and so become sexually mature and much larger than other bees Drones are hatched from unfertilised eggs and so only receive genes from the queen. Their role in a hive is almost solely for reproduction, and they leave the hive daily in search of 'virgin queens'

"She will fly to this place at about two o'clock in the afternoon, mate with, let's just say, a large number of males, 30, 50 … and she'll go home again about 15-10 minutes later, really quick," Professor Oldroyd said.

"And the males die after they do it, that's a little bit of juicy gossip. They turn inside out like a rubber glove!"

Once mated, the queen will either return to her original hive where she will replace her mother, or take a swarm of worker bees from her original hive to start a new hive.

Then she will use the stored sperm to continue to fertilise eggs for several years.

Mr Withrow says that scientists know mating with a lot of drones brings genetic diversity to the hive, but still aren't clear why they mate this many times.

"It could be something like: when they mate, the queen only takes up a small amount of the actual sperm from each drone, it could be that some of these drones are not getting very many of their sperm in the spermatheca, so they are fathering such a low number.

"I think that it's clearly not simply just that 'if a little bit of genetic diversity is good, a lot more genetic diversity is even better', because they [the many mates] are not represented in the overall worker population," Mr Withrow said.

"So it's more like some sort of specialised thing going on that we just don't really know what that is yet."

Scientists would expect the queens to get some benefit from these extra mating events, given the risk and energy it takes the female to go on multiple mating flights, but as yet the benefit remains unclear.

A queen bee larvae is fed by attending worker bees; as she grows she is kept in a "queen cup", a modified cell built to accommodate her much larger body. ( Supplied: Benjamin Oldroyd )

"Each additional flight they go on brings up the risk that they either get lost, or they get picked off by a bird, or some other kind of predator, or something like that and so that's, every mating with more drones, the degree to which that means going on more mating flights means more risk in that way," Mr Withrow said.

More research needs to be done to fully record bee behaviour and understand why it occurs.

"While we already knew that queens mate with a large number of drones, this study is suggesting that's a lot more than has been previously recognised, because a lot of those drones that queens are mating with are actually only fathering a very small number of her total offspring," Mr Withrow said.

What makes a queen bee different?

In a hive, when a queen dies suddenly, there may not be a specially laid larva that can replace her.

In this case worker bees will choose an ordinary worker larvae and feed her a more nutritionally dense diet of exclusively royal jelly for that female to become sexually mature.

In his research, Mr Withrow discovered that when a hive needed an emergency queen, some larvae from certain families (meaning fathered by the same drone) were being selected as replacement queens far more frequently than others.

According to both Mr Withrow and Professor Oldroyd, the big question is: if there is a gene that some males have that makes their offspring more desirable as queens, and as queens are the ones that get to reproduce the most, and therefore pass their genes on, how is it that more bees don't have this gene?

All bee larvae develop in the cells in a honey comb. Those on the right are slightly older than on the left. ( Wikimedia Commons )

"Anything that greatly increases or greatly decreases your fitness should immediately get either selected right through the population or be removed from the population," Professor Oldroyd said.

Mr Withrow says it is really an unknown at this point, with theories yet to be tested, but says it should not be forgotten that this behaviour was observed in hives where only emergency queens were being created and that this does not happen often.

Mr Withrow says this research is interesting, first from a basic science idea that just learning more about the natural world and how cool things are is worthwhile and interesting in itself, but also as we rely on bees for many aspects of agriculture, it is really important we try to understand them.

"There's increasing problems with keeping them around in the numbers that we need for our agricultural production … learning more things about them gives us more tools and strategies for how to develop new ways to help keep them around like we need."