With honeybees, the queen uses a special fragrance to ensure that her workers remain sterile and serve her. Researchers have now also identified such a queen pheromone for the first time in a bee species with a far simpler state – the furrow bee. The surprise, however, is that the queen’s fragrance consists of a chemically completely different substance than that of honeybees. This indicates that the evolution of these pheromones was more complex than previously thought.
There is a strict division of labor in the state of honey bees: the queen alone is responsible for reproduction and egg laying. The task of the workers, on the other hand, is to take care of the queen, raise the brood and provide food for the stick. A fragrance secreted by the queen bee – the queen pheromone – ensures that the workers do not develop ovaries and do not become sexually mature. You cannot produce offspring yourself. This reproductive division of labor and the caste system are regarded as the basis for the success of eusocial insects such as bees, wasps or ants.
Do furrow bees also have a queen pheromone?
But there are also bees that also live socially, but have less pronounced box differences. The furrow bee Lasioglossum malachurum belongs to these primitive eusocial bees. Their annual colonies consist of far fewer individual animals than honey bees or wasps and queens and workers hardly differ on the outside. Therefore, researchers have previously assumed that these bee species do not need queen pheromones. Instead, the queen ensures through her aggressive and dominant behavior that her workers do not mate and reproduce – so the common assumption. However, this has not been proven so far.
That is why Iris Steitz from the University of Ulm and her colleagues have now tested this assumption in experiments with the furrow bee. It was already known from previous studies that these bees have different fragrances on their skin, including hydrocarbon chains of different lengths and also ring-shaped esters, so-called macrocyclic lactones. It was already known that these substances are more abundant on the queen’s cuticle than among workers. However, it was unknown whether one of these substances might act as a queen pheromone.
This is where the experiment by Steitz and her team comes in. To do this, they put two workers in a transparent tube and observed their behavior when they met. The highlight: the researchers had previously coated one of the animals either with a queen’s fragrance mixture or with a different mixture of cuticular hydrocarbons and macrocyclic lactones.
Available, but surprisingly different
The tests showed that the Queen’s original secret actually provoked a typical reaction from the worker: “The typical reaction consists of submissive, withdrawing movements,” explains Steitz ’colleague Manfred Ayasse. Deceived by the scent, the test bee in the tube also showed this submissive behavior towards her “perfumed” colleague. According to the researchers, this suggests that the queens of furrow bees also use a fragrance signal to control the behavior of their workers.
But what is this pheromone made of? This was shown by the reaction of the workers to the synthetic fragrance mixtures. When they encountered a nestmate coated with macrocyclic lactones, they behaved as if they were a queen. In contrast, if the workers only carried a mixture of the cuticular hydrocarbons, the submissive reaction failed to materialize. According to the researchers, the furrow bee queen pheromone appears to consist of macrocyclic lactones. As additional tests confirmed, these fragrances also inhibit the development of the ovaries in the workers.
It seems clear that primitive eusocial bees like the furrow bee also use a queen pheromone – contrary to previous assumptions. Also surprising: “Most of the studies published so far suggest that cuticular hydrocarbons have evolved into queen pheromones in all social insects,” says Ayasse. “Our study questions this assumption and shows a much more complex picture of evolution.”
Source: University of Ulm; Technical article: Current Biology, doi: 10.1016 / j.cub.2020.01.026