How Bees Communicate with Pheromones

How Honey Bee Pheromones Work in the Colony

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Pheromones are a chemical communication system between an animal and others of its species. In fact, the phrase “communication system” may be too passive a description—at least in the insect world, where pheromones secreted by one individual can elicit behavioral or physiological response by others of their kind.

Nasanov. Photo credit: UMN Bee Squad.

Honey bees are eusocial, meaning they live in highly complex social colonies, with multiple casts and tens of thousands of individuals of overlapping generations. A complex ambient of pheromones is what coheres these thousands of individuals into one thing (a superorganism), allowing the colony as a whole to maintain homeostasis. While pheromones are usually species-specific, those of us belonging to other species can listen in, and begin to decode the tangle of chemical signals for our own purposes.

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Varroa mites, for example, listen in on the brood pheromones of honey bees. Brood ester pheromone (BEP) is a chemical compound that older larvae produce to regulate (among other things) when workers cap brood cells. Female mites wait for the “cap me” signal produced by 5th instar larvae before they sneak into open brood cells. Soon afterwards, nurse bees cap over those cells with wax, providing the foundress mite the ideal atmosphere for reproducing. Taking advantage of chemical cues, the foundress synchronizes her egg-laying schedule with the bee’s growth, so that her offspring can complete their development before the host bee emerges from the cell. Gross!

Beekeepers, too, can listen in on the language of honey bee pheromones. With our vaguely-proficient noses, we can only detect one or two of a colony’s chemical signals. But even those that we cannot smell are worth studying, because understanding pheromones in the hive can help us become better beekeepers.

Some pheromones are called “primer” pheromones. They affect the bees at a physiological level, and they are long-term. For example, a queen secretes a pheromone from her mouthparts called queen mandibular pheromone (QMP). QMP gives a colony a sense of being “queen right,” and stimulates workers to groom and feed the queen, build new wax, forage, and care for brood; this pheromone is also partially responsible for suppressing the maturation of worker bee ovaries. QMP is picked up by the queen’s retinue (the ever-changing guard of workers tasked with grooming the queen) and spread through the colony as workers walk across the combs, feed each other (trophallaxis) and touch antennas. Without a strong QMP signal, the workers will build queen cells in an attempt to replace what they perceive to be a failing queen. Or, if there is no brood present, their ovaries may be activated and they may start laying unfertilized (male) eggs—a last-ditch effort to perpetuate their genetics.

Alarm Pheromone. Photo credit: UMN Bee Squad.

Brood pheromones are similarly important to the colony’s functioning and sense of “rightness.” The open brood pheromones (namely e-beta-ocimene in young larvae and fatty acid esters present on the cuticle of older brood) affect worker bee behavior. Through pheromones, those little larvae compel workers to forage for them and feed them. Like queen pheromone, the brood esters help to suppress workers’ ovaries. Understanding the role of brood pheromones can help us understand why our bees do weird things like supersede a young, presumably well-mated queen in a recently-hived package colony: even after she begins laying, there’s a length of time when open brood and its manipulative scent isn’t present. The bees may interpret the lack of brood pheromone as “not right” and seek to replace their queen.

While primer pheromones help to maintain the checks and balances of long-term colony functioning, “releaser” pheromones generate short-term, behavioral responses. You are probably familiar with some releaser pheromones already. Alarm pheromone is a releaser, and smells like ripe bananas. Bees produce alarm pheromone when they sting, or when they open the sting chamber at the tip of their abdomens. Even if you can’t smell bananas, you can identify the posture of an alarmed bee: her abdomen is pointing straight up and her stinger is visible.

Beekeepers use smoke to inspect their colonies in part to mask the scent of alarm pheromone; to disrupt the bees’ message that it’s time to defend. A beekeeper who is fully covered in protective gear may not feel stings or smell alarm pheromone on their clothing, and so with each movement they increase the defensiveness of the colony they are working. Alarm pheromone reminds us that we need to slow down and move more carefully as we work a colony.

Have you smelled lemony Nasonov pheromone before? It is the pheromone bees use to orient each other to “home.” Older workers will help new foragers orient to their hive location by secreting Nasonov at the entrance of the colony, fanning their wings madly to make their point. The posture of Nasonoving bees at first might look similar to alarm-producing bees. In both cases, their abdomens are raised, but Nasonov is produced from the 7th abdominal tergite, which is best described as near the end of the abdomen on the “top side” of the bee. When that gland is open (it looks white), the abdomen’s point appears to have a slight downward crook.

I think Nasonov is the pheromone beekeepers take advantage of most. Whenever bees are producing it, they are docile. Working a defensive colony, a beekeeper might shake a frame of bees in front of the hive entrance to induce them to start nasonoving, helping their sisters home, and in the process masking alarm pheromone. Some beekeepers add a Nasonov-mimic, lemongrass, to attract swarms into empty equipment, or to entice bees to take down syrup given as food supplement in the fall.

There’s a lot more to discuss when it comes to honey bee pheromones. But still more remains mysterious. Exactly what chemical signals trigger hygienic bees to remove Varroa-infested larvae? Is it the same or different chemicals than those that sick brood signal with? Is some brood better at signaling than others? Or is it all about the workers’ proficiency in picking up signals?  Do mites give chemical signals that bees can detect? Do drones use special pheromones to orient to mating areas? What about you? What honey bee pheromone mysteries are you interested in solving?

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