‘Queen Substance’, the pheromone attracting drones
(The Telegraph) Until the 1950s, what causes the workers to produce a new queen to replace one which is failing, or has been lost, was a mystery.
As any beekeeper will know, when a queen is removed from a colony the behaviour of workers changes from a state of organised activity to one of restlessness. After a few hours, they will have modified one or more cells containing female larvae into emerging queen cells.
Colin Butler, who has died aged 102, was one of the world’s most distinguished entomologists and was credited with the discovery of a pheromone known as “queen substance”, a scientific breakthrough which transformed our understanding of the social behaviour of bees.
Traditionally, beekeepers assumed that the queen must emit some sort of odour which keeps workers aware of her continued presence, the absence of which causes them to begin rearing new queens. To test this theory, Butler placed a queen in the middle of her hive in a wire gauze cage, so that surrounding bees could not touch her, and found that the workers began to behave as if they had lost her, rearing new queens.
He concluded that some sort of physical or chemical signals from the queen to keep the colony loyal were being transmitted, not through smell, but through physical contact with the few workers attending her. No one had reported seeing any physical signals, so the latter theory, that the queen emits some sort of chemical substance, seemed the more plausible.
Butler then compared the behaviour of workers that had left the queen after licking the special wax which covers the queen bee’s body, with those of other workers which had examined her body with antennae, but not licked her. Each of the bees that had licked her body offered regurgitated food to other colony members within the first five minutes of licking her, while the other bees did not.
In other experiments he observed that if a queen was rubbed with a piece of cotton wool, the cotton wool became as attractive to worker bees as the queen herself.
He also found that the number of bees which any given queen can inhibit from rearing new queens varies quantitatively with the amount of contact allowed between queen and workers; and when material from the digestive tracts of workers which had licked the queen was added to the drinking water of groups of queen-less bees, the ovaries of those bees developed much less than control bees without the additive.
His conclusion was that of all the factors that keep members of a colony of bees together, “the strong desire for ‘queen substance’ is probably the most important”. He went on to show that queen substance is produced in the mandibular glands of the queen, and in 1959 a collaboration with Robert Kenneth Callow led to its identification as 9-oxodec-trans-2-enoic acid.
They also showed that this acted as the sex-attractant for drones when deployed at about 10 metres above the ground, the height at which queens fly on their “nuptial flight”, the first demonstration of a sex-attractant pheromone.
In 1955 Butler suggested that “either a deficiency in the amount of queen substance available, or, perhaps, a breakdown in its collection and subsequent distribution plays an important part in the phenomenon of swarming”, when a honeybee colony divides to produce two colonies and which can be a headache for beekeepers.
The discovery of queen substance raised hopes that synthetic chemicals might be developed to control swarming and Butler went so far as to get a patent on synthetic “queen substance” with the idea of marketing it for swarm suppression and to facilitate the introduction of replacement queens into unwilling honey bee colonies, and also as a possible human contraceptive.
Unfortunately, he was wrong. Bees still swarmed and it had no action in humans. He concluded that other factors, perhaps even psychological reasons, were involved. The mechanisms of swarming remain something of a mystery to this day.