Access for stick members only! How do guardian bees at the nest entrance differentiate between comrades and potentially thieving strangers? For the formation of the nest odor, the common features of the intestinal flora of the hive are decisive and not the genetic similarities, according to a study. The microbes therefore not only have an impact on the health of honey bees, but also on their social behavior, say the researchers.
There is strict control at the entrance to the hive: in addition to predatory insects, the guardians of one colony must also refuse access to bees from other countries. Because the insects are by no means as friendly to one another as one might think: “In autumn, when the plants are no longer producing nectar, there is a time when theft between colonies is very common,” says Cassondra Vernier of Washington University in St. Louis. If a nest is not properly guarded, it can be plundered, the scientist emphasizes. For this reason it is important for the survival of colonies that the members can distinguish their nest mates from foreign bees.
What is the smell of the members?
It is already known that honey bees use special patterns of chemical signals for this purpose. They are based on volatile compounds, the so-called cuticular hydrocarbons or CHCs. They form a kind of common smell, by which the members recognize each other. One might assume that this signature is based on the close genetic relationship of the individuals of a people. But as Vernier and her colleagues report, there are already indications that this is not the case. Because if you put young animals up to a certain age and stage of development in foreign bee colonies, they will be accepted and then perceived as belonging to the colony. “So it has to be something that you have acquired over the course of your life that is the key factor,” says Vernier. So the composition of the intestinal bacteria of the insects became the focus of the researchers.
Like other living things, bees also have an intestinal flora that plays an important role in their digestion and immune system, as studies have already shown. As part of their study, Vernier and her colleagues have now examined the composition of the microbiome of different bee colonies using genetic methods. Using gas chromatographic analyzes, they also examined the profiles of the CHCs that make up the “member odor”. The scientists also carried out exchange experiments in which groups of newly hatched bees were transferred to unrelated bee colonies.
The intestinal flora determines the smell
They were initially able to confirm that colonies not only have different CHC profiles – the composition patterns of the bacterial communities in the bees’ intestines also differ in characteristic ways. “Different bee colonies actually have colony-specific microbiomes, which has never been shown before. This is explained by the fact that bees constantly share food with one another – so they only exchange their microbiome within their colony, ”says Vernier.
The researchers then found evidence that the CHC profiles are in turn influenced by the characteristics of the intestinal flora. It was shown that the microbiome of bees in a colony can be manipulated by feeding the newly hatched bees with special microbes. These bees then not only develop different microbial communities in the intestine, but also changed CHC profiles, the analyzes showed. And this effect was also noticeable: “These bees were unrecognizable for their siblings. The manipulation of the microbiome was enough to induce the bees of a colony to develop different odor profiles, ”says Vernier.
The bottom line is that the results show that the special CHC profile of a bee is not only innate or genetic, but depends on the bacteria that form the microbial community in their intestines, the scientists sum up. They suspect that the respective bacterial communities produce certain metabolic products, which in turn are responsible for the formation of a characteristic CHC profile.
“The importance of this work is that it provides evidence that the microbiome not only affects honeybees’ health, but is also involved in their social biology,” says Vernier. “It apparently influences how the bee colony functions as a whole and how it is able to maintain the nest defense, and not just the immune defense in the body of an individual,” says the scientist.
Source: Washington University, Article: Science Advances, doi: 10.1126 / sciadv.abd3431