Social response of healthy honeybees towards Nosema ceranae -infected workers: care or kill?

Honeybees are living densely packed in colonies which extremely facilitates intracolonial pathogen transmission from one individual to another. In addition to the defence by the innate immune system, various behavioural adaptations allow honeybees to avoid or reduce pathogen transmission, also coined ‘social immunity’. Here, we show that infections with the intestinal parasite Nosema ceranae lead to altered behaviour going beyond a ‘care-kill dichotomy’ within the society. We show that the response of healthy workers can be highly variable ranging from avoidance to enhanced social interactions that even lead to killing of infected nestmates in some cases. These behavioural defence mechanisms may help in reducing the spread of the disease in the colony. Thus, honeybees can respond highly variable and not just with one behavioural response after recognising an infected worker even when fighting against the same parasite species.