Bees use social distancing strategies to protect themselves from parasites

A new study by an international team led by researchers from the University of London in the UK and the University of Sassari in Italy has found that when bees' hives are threatened by parasites, they increase social distancing to prevent the spread of bad conditions. The study, published in Science Advances, shows that bee colonies respond to infestations by harmful mites, increasing social distance between young and old bees by changing the use of space and interactions between nesters.

Co-author Dr Alessandro Cini (Center for Biodiversity and Environmental Studies, UCL School of Biological Sciences) said. "Here, we provide the first evidence that bees have altered their social interactions and the way they move in their hives in response to a common parasite. Bees are social animals because they benefit from shared responsibilities and interactions, such as cleaning up bodies from each other, but when these social activities may increase the risk of infection, bees appear to have evolved to balance risk and benefit by employing social distancing. "

In animals, examples of social distancing have been found in very different species that evolved millions of years apart: from baboons in individuals with gastrointestinal infections to ants infected with a disease-causing fungus, all have similar behaviors.

The new study assessed whether the presence of the parasite tile mite in bee colonies induces changes in social organization, thereby reducing the spread of parasitic mites in the hive. Among the stressors that affect bees, the tile mite is one of the main enemies of the bee colony, as it causes many harmful effects on the bees at the individual and colony level, including virus transmission.

Bee colonies are organized into two main compartments: the outer compartment is occupied by foragers and the innermost compartment is inhabited by nurses, queen bees and larvae. This spatial isolation within the colony allows the interaction between the two compartments to be less frequent than within each compartment, and allows the most valuable individuals (queen bees, young bees, and larvae) to be protected from external environmental influences, thus avoiding the onset of disease.

By comparing swarms that were infested or uninfected by the wattle mites, the researchers found that if the hive is invaded, a behavior that can increase mite transmission— the foraging dance, occurs less frequently in the central part of the hive. They also found that grooming behavior became more concentrated in the central hive. Overall, the researchers say, the foragers (older bees) move toward the periphery of the nest, while the younger feeder and groomer bees move toward the center of the nest in response to infestations, increasing the distance between the two groups.

Lead author Dr Michelina Pusceddu (Department of Agronomy, University of Sassari) said. "The observed increase in social distance between two groups of bees in a colony of the same parasite infection represents a new, and in some ways surprising aspect of how bees evolved to fight pathogens and parasites." Their ability to adapt to social structures and reduce contact between individuals to cope with disease threats allows them to maximize the benefits of social interaction where possible and minimize the risk of infectious diseases when needed. It can be seen that the bee colony provides an ideal model for studying social grooming and fully understanding the value and effectiveness of this behavior. "