This summer, I was checking a beehive which had just hatched a new queen. I was hoping that the queen had mated and started laying. I looked for eggs. There were eggs, but they were multiple eggs in a cell, and they had been laid haphazardly, not neatly with a single egg to a cell as one would expect. There was no queen, but, horrors! there was a laying worker!
Laying workers are a bane of beekeepers. In the absence of queen bee pheromone, the ovaries of a worker are released from repression, making her an ersatz queen. She starts laying eggs, but her squat abdomen does not reach the bottom of the cell, and so her eggs are laid willy-nilly. Since she has not mated, her eggs are all fated to develop into unfertilized male drones, rather than fertilized female workers. The decline of worker bee numbers and the increase in drone numbers is fatal to the hive. Unless the laying worker is quickly removed and a new queen installed, the hive is doomed to failure. But if the laying worker entrenches herself in the hive, her pheromones will permeate the hive and her loyal retinue will quickly kill a newly introduced queen. I got rid of the laying worker by shaking every single bee out and then restoring the hive to its original location. The theory is that every bee except the laying worker, who will be too heavy with eggs, will fly back to the hive. After a day or two to allow the laying worker’s pheromones to disperse, a new queen can be introduced. Her pheromones will permeate the hive and engage the workers’ loyalty as well as keep their ovaries from developing. The hive is back in business.
Just as hormones are the chemical messengers within a body that can quickly pivot it to dealing with new threats or opportunities, pheromones are chemical messengers released by an individual that communicate important information, usually within the same species. Thus bee alarm pheromone can turn a placid hive into a raging tornado within an instant. Sex pheromones can attract suitors from a wide area to an available partner. Trail pheromones can lead other members of the tribe to a souce of food or water. Spawning pheromone ensures that eggs and sperm are simultaneously released by aquatic animals such as coral anemones to ensure that they can find each other in the vast ocean. Aggregation pheromones call members of a species such as locusts together, to form swarms consisting of millions of individuals which can decimate all plant life in their path. An enjoyable experiment I used to do with my first-year biology students was to have them draw a convoluted closed circle on paper using “Bic” ball-point pens, and then introduce some termites. The termites would promptly make a conga-line on the ink line and follow it around every bend. A chemical in the ball-point pen’s ink was similar enough to the trail pheromone that the animals followed it. It never failed to please and my students usually walked out starry-eyed: Who would’ve thought we could get termites to walk in line?
All communication mechanisms work on the signal-reception-response pathway. Animal pheromones are sensed in the target’s vomeronasal organ (VNO; also known as Jacobson’s organ), a pair of sensory organs that lie above the hard palate of the mouth. Sensory neurons from the VNO stimulate hypothalamus where hormones are secreted in response to pheromones, which themselves activate other physiological responses such as ovarian development and egg-laying in worker honeybees. The first pheromone isolated was bombykol, a sex pheromone produced by female silk moths. It was isolated in 1956, after 20 years of painstaking work by Adolf Butenandt’s team, who crushed over half-a-million female moth abdomens and then fractionated the sludge to isolate a tiny tiny amount of the pheromone. The scientists followed the fraction that contained the pheromone by employing live male moths as a bioassay, checking their antennae for vibrations in reaction to the female pheromone.
Pheromones may have both “releaser” and “priming” effects on the target. Releaser effects are manifested immediately, such as raising an alarm or attracting a male for mating. Delayed priming effects cause other or lingering outcomes. Sex pheromones may both attract the opposite gender, but may also stimulate egg or sperm production which takes place over a longer time period through secondary messengers, as discussed above. Queen pheromones can trigger loyalty as well as suppress egg-laying in female worker honeybees. A hormone called oxytocin has been suggested to also function as a loyalty pheromone as well as a biological hormone. Apparently mothers and babies produce a surge of oxytocin when looking in each others’ eyes [1], but so also do dogs and their owners, replicating a parent-child bond. Apparently, oxytocin’s ability to engender trust has been commoditized – it is now a component of certain perfumes one can buy. What’s not to love? Well, some psychologists think the downside is that it may exacerbate the separation of an in-group from an outgroup, potentially deepening social divisions [2].
Another interesting thing is that we all have a distinct odor consisting of a “signature mix” of odorant molecules which is individual-specific [3], including pheromones that may signal fitness to potential sexual partners. It is conjectured that these signature odors contain information on relatedness; thus one finds sweat of a closely-related person of the opposite sex less alluring than someone who is not related. Sweat may also carry pheromones signaling stress and fear – dogs are said to “sense” when someone is fearful. Beekeepers know that bees also have this talent. Tristam Wyatt cites Charles Butler in The Feminine Monarchie (1609) that if you are stung by one honeybee, “other Bees smelling the ranke favour of the poison cast out with the sting will come about you as thick as haile” [3]. Beekeepers have to let go of the fear of being stung, and focus on staying calm and moving carefully to avoid triggering the release of bee alarm pheromone that can instantly change a hive of bees into a buzzing, stinging mass.
Wouldn’t it be nice to have a “bee-loved” pheromone?
1. Kekecs, Z., et al., Commentary: Oxytocin-gaze positive loop and the coevolution of human–dog bonds. Frontiers in neuroscience, 2016. 10: p. 155.
2. Ten Velden, F.S., et al., Oxytocin differentially modulates compromise and competitive approach but not withdrawal to antagonists from own vs. rivaling other groups. Brain research, 2014. 1580: p. 172-179.
3. Wyatt, T.D., Fifty years of pheromones. Nature, 2009. 457(7227): p. 262-263.
