How do bees not get sick? The question is less obvious than it might seem: after all, they live in colonies of tens of thousands of specimens, crowded together in very narrow spaces, an ideal condition for the transmission of pathogens, in theory. We know that for this reason bees have developed different defense systems, but we have always considered them separately. Now, a study published on ISME Communications demonstrates for the first time that their secret is in the hives, which are built as a single immune system composed of different parts that “collaborate” and deal with different aspects of defense against parasites.
Defensive architecture
As mentioned, we already knew that all the substances produced by bees and kept in the hives have some antimicrobial properties: this applies to honey, wax and also propolis.
What we had not yet studied is the internal organization of these different defenses; to find out, the Australian team that conducted the study analyzed 24 hives of Apis mellifera of New South Wales, analyzing the antiseptic properties and chemical content of both the aforementioned substances and the different microbiomes into which a colony is divided: the entrance, the honeycombs (including those where the queen lays her eggs), even the stomachs of the bees themselves.
The analysis first confirmed the antimicrobial properties of the substances present in the hives, but above all it identified a real gradient in the bees’ defenses. Substances with a very broad spectrum of action act at the entrance to the hives, but are less effective than specialized ones.
The closer you get to the center of the colony, where the concentration of bees also increases, the more the defenses focus on bacteria, in particular Paenibacillus larvae And Paenibacillus alveiboth potentially lethal to a colony.
The role of flowers
Even individual bees contribute to the immune defenses of the hives, absorbing toxic substances and purifying them, or in any case preventing them from reaching the queen (provided they do not find a virus that deceives them). In general, defenses against fungal infections are less present, rarer and less lethal, not to mention the fact that many fungi can even bring benefits to beehives.
Another element that influences the composition of the immune defenses of hives are the flowers present in the environment, which determine which chemical substances are available to the bees (pollen also has antibacterial effects).
Finally, the researchers noticed that the more stressed a colony is, the more disorganized its immune defenses become: according to the authors, this is proof that the environment has a decisive influence on the health of a colony, and that a hive surrounded by flowers is a healthy hive.
