From plaster to pesticide. The use of propoolis by honey bees to control their major ectoparasite

Self-medication refers to the ability of animals to exploit beneficial biologically active compounds in response to parasite infestation. Recent studies suggest that Apis mellifera may adopt such behaviour against the mite Varroa destructor, the most important ectoparasite of the honey bee. Here we describe for the first time a novel line of defence in the behavioural immunity repertoire of honey bees, which involves the use of propolis to treat the environment where the parasites reproduce. We found that propolis applied to brood cells can affect mite mortality and fertility, with a positive effect on bees and a clear impact on Varroa population. We conclude that propolis can be regarded as a potent natural pesticide used by honey bees to limit a dangerous parasite. Our findings show that increased resin collection represents an example of social medication that is performed by honey bees to mitigate the detrimental effects of Varroa parasitism.