Science / Medicine : Nature’s Potent Perfume : The aromatic natural oils of a queen honeybee send chemical messages that enable her to rule a hive of thousands of workers, scientists have found. Synthetic bee oils can be used to raise crop yields and control killer bees.
Beekeepers and biologists have long known of the phenomenon of “queenrightness.” When the queen bee is home, the life of a honeybee colony is the picture of happy, efficient, cooperative living--the colony is queenright. But if a queen disappears from her hive, within as little as an hour there is growing tension among the workers. The disgruntled bees are less willing to work at their important tasks, including the collection of pollen and nectar.
“When you take the queen away, bees get very agitated,” said Mark Winston, head biologist on the honeybee queen research team at Simon Fraser University in British Columbia, Canada. “And when they are agitated they also begin dying more quickly. Because it keeps the bees alive and working, maintaining queenrightness is clearly very important for beekeepers.
Queenrightness has also held a fascination for biologists who wanted to understand how each of the tens of thousands of worker bees could know whether their queen was actually present in the hive or not. But despite the interest, queenrightness remained a mystery until recently, when Winston, Keith Slessor and their colleagues at Simon Fraser began unraveling the chemical and biological threads of the story.
Their findings not only have shed light on bee behavior but also have implications for increasing the production of important crops, trapping swarms of angry killer bees and perhaps breeding specific strains of bees.
The key seems to lie in the natural perfume oils oozing from the queen’s mouth. First, the group was able to show which of the many substances in the oils were actually being recognized as chemical messages, or pheromones, by the workers.
The scientists did this by observing which selected oily mixes cause retinue behavior. As part of this behavior, the workers closely encircle their queen, lick her with their tongues and touch her with their antennae, collecting as much as they can of the aromatic oil that has leached out of the queen’s mouth and onto her body.
Soon the researchers had identified the five active chemicals that made up the retinue-inducing pheromone. After identifying the active chemicals, the next big advance came when the researchers discovered that the retinue-inducing pheromone they had been studying was actually responsible for queenrightness.
They set up three types of hives: Those with queens inside, those without queens and those without queens but with queen pheromone sprayed inside. Their experiments showed that pheromone spray could fool whole hives of workers into acting as though the queen bee were present even though she was not. Like the hives with queens, these queenless hives that were sprayed with pheromone were perfectly queenright. Those without queens or pheromone elicited no such response.
Why should a chemical that makes the workers think the queen is home make them calm and keep them efficient at their food-collecting jobs? Because, say the researchers, without her, they know that their world may be falling apart.
When a queen dies or is somehow removed from the hive, it is as though the hive has had its reproductive organs removed, an event that would cause a creature to panic.
Only the queen can lay the eggs that can become workers and future queens. And when workers can’t smell the royal perfume, it tells them that if they do not raise a replacement queen fast they will soon become “hopelessly queenless.”
“There’s about a seven-day window during which the hive can make new queens from the old queen’s eggs,” said Winston. “If they don’t do it quickly, the hive is a dead end.”
In addition, the workers in hopelessly queenless hives stop cooperating, and it is “every bee for itself.” So at the first smell of potential queenlessness, the usually diligent workers become less interested in gathering food for the entire colony and more interested in looking out for No. 1.
The researchers have since discovered that the pheromone is as attractive to bees in the field as it is in the laboratory and that this attractiveness can be powerfully exploited.
“We happened to put out some lures with the pheromone in it in the field,” said Winston, “and the bees just glommed right onto them. We thought, ‘Well you know this stuff is so attractive maybe we can just spray it on crops.’ ”
In orchards that were sprayed with the pheromone, more and more bees would come in to scour the fruit trees or bushes for pollen and nectar. With more and more bees visiting, more and more flowers were pollinated and more and more fruit was produced.
By spraying crops with the pheromone, Winston, Slessor and their colleagues have been able to increase crop yields of pears, cranberries and blueberries, sometimes by as much as 30%, simply by bringing in the bees. To a farmer that can mean an increase in profits of $4,000 per acre or more.
But the usefulness of this powerful pheromone has extended beyond helping the farmer in the field to helping people living in areas of the country threatened by killer-bee swarms.
“We’ve already caught swarms of killer bees using traps baited with the pheromone,” said Slessor, the head chemist on the team. “Now we’re continuing tests to see just how attractive these traps really can be.” The growing potential for application of this pheromone is so great that the synthetically produced chemical has been patented and it can be bought as a commercial product.
In their most recent work, the honeybee research team labeled the queen pheromone with a radioactive tag and tracked the fate of the pheromones removed from the oily queen by her retinue. According to Tom Seeley, a Cornell University expert in honeybee behavior, a longstanding mystery about queenrightness had been how “a single individual (the queen) could relay the message ‘I’m here’ to thousands and thousands of individuals.”
The Simon Fraser scientists were able to prove that it was the worker bees that relayed this message throughout the gigantic colonies. Known as “messenger” bees, the workers cover themselves in royal pheromone oil and zip around the hive sharing the pheromone with their co-workers. When the messengers are through, every co-worker they have encountered has had a dose of this honeybee Valium from the queen.
Scientists also knew that the queen needed to send messages out constantly to ensure frequent deliveries to each of the thousands of workers, according to Seeley. But these messages had to be destroyed quickly. The only way the worker bees can be sure that the queen is still alive and safe is to continually receive new messages. If the chemical message lingers long after the queen sends it, the bees would have no way of knowing if she had died or disappeared. The radioactive tags confirmed that, to ensure that no one is getting old news, the workers eat the messages.
The latest efforts of the Simon Fraser group are aimed at understanding the genetics behind the workers’ response to the queen pheromones. If, as the researchers suspect, the tendency to react strongly or weakly to the pheromone is inherited, then there is the potential to develop lines with differing levels of reactivity. One day, a farmer may be able to run to the store and pick up a package of highly reactive bees and two quarts of pheromone to pollinate this summer’s crops.
Talking Pheromones
A pheromone is a chemical message sent out from one animal to another animal of the same species. Many creatures--including bees, snakes, salamanders, deer, even humans--produce these messages, which indicate anything from “I’m home” to “Let’s have sex” to “Follow me” to “There’s something terribly wrong!”
