When faced with the threat of a parasite, bees employ distancing measures in a way similar to other social insects.
With the appearance of Covid-19, everyone has become familiar with the concept of social distancing to minimise the spread of disease. But actually this is not a new behaviour – the use of social distancing is not uncommon in social insects. Fungus-infected ants have been shown to self-isolate within hours of being exposed,1 and when confronted by fungal spores, some species of termite begin vibrating to inform their nestmates that they need to be avoided or to trigger mass grooming.2 Similarly, new research has shown that honey bees implement social distancing measures when their hive is under threat from a parasite.
An international team involving researchers at UCL and the University of Sassari in Italy examined the behaviour of a honey bee colony after introducing one of its common enemies, the Varroa mite (Varroa destructor).3 The ectoparasite mite (pictured above), which forager bees would typically encounter on flowers, presents a serious health risk to bees at both an individual and colony level, including the transmission of a number of viruses. Published in Science Advances, the study demonstrated that honey bee colonies respond to Varroa mite infestation by modifying the use of space and the interactions between nestmates to increase the social distance between young and old bees.
Honey bee colonies are organised into two main compartments: the outer one occupied by the foragers (old bees) clumped together near the entrance of the hive, and the innermost compartment inhabited by nurses (young bees) with the queen. By separating the two groups of young and old bees, the most valuable individuals – the queen, young bees and brood – are protected by the outside environment and thus from the arrival of diseases.
In response to the Varroa mite infestation, the researchers noted that the bees appeared to be increasing the distance between the two groups, with foragers (older bees) shifting towards the periphery of the nest while young nurse and groomer bees moved towards its centre. They also found that grooming behaviours became more concentrated in the central hive. The bees modified their behaviour in other ways, too. Bees are known for their foraging dances, which they use to communicate the exact position of a food source to other foragers. When forager bees were affected by the mite, researchers noted that foraging dances (round and waggle) occurred less frequently in central parts of the hive. As the performance of communicative dances would be likely to increase mite transmission, it appears that the bees changed their behaviour to mitigate the risk of disease spread.
Lead author Dr Michelina Pusceddu from the University of Sassari commented that the observed increase in social distancing between the two groups of bees within the same parasite-infested colony represents a new and, in some ways, surprising aspect of how honeybees have evolved to combat pathogens and parasites. “Their ability to adapt their social structure and reduce contact between individuals in response to a disease threat allows them to maximise the benefits of social interactions where possible, and to minimise the risk of infectious disease when needed.”
It appears that similarly to termites and ants, bees have evolved to balance the risks and benefits of their usual social activities of grooming and communication when faced with the possibility of infection.
1 N. Stroeymeyt, A. V. Grasse, A. Crespi, D. P. Mersch, S. Cremer, L. Keller, Social network plasticity decreases disease transmission in a eusocial insect. Science 362, 941–945 (2018).
2 Bulmer, M.S.; Franco, B.A.; Fields, E.G. Subterranean Termite Social Alarm and Hygienic Responses to Fungal Pathogens. Insects 2019, 10, 240.
3 Pusceddu, Michelina & Cini, Alessandro & Alberti, Simona & Salaris, Emanuele & Theodorou, Panagiotis & Floris, Ignazio & Satta, Alberto. (2021). Honey bees increase social distancing when facing the ectoparasite Varroa destructor. Science Advances. 7. 10.1126/sciadv. abj1398.
Reworked extract from: University College London. Honeybees use social distancing to protect themselves against parasites. Science Daily, November 1, 2021