Honeybees use propolis as a natural pesticide against their major ectoparasite

Abstract

Honeybees use propolis collected from plants for coating the inner walls of their nest. This substance is also used as a natural antibiotic against microbial pathogens, similarly to many other animals exploiting natural products for self-medication. We carried out chemical analyses and laboratory bioassays to test if honeybees use propolis for social medication against their major ectoparasite: Varroa destructor. We found that propolis is applied to brood cells where it can affect the reproducing parasites, with a positive effect on honeybees and a potential impact on Varroa population. We conclude that propolis can be regarded as a natural pesticide used by the honeybee to limit a dangerous parasite. These findings significantly enlarge our understanding of behavioural immunity in animals and may have important implications for the management of the most important threat to honeybees worldwide.

Keywords: Apis mellifera; Varroa destructor; natural pesticide; propolis; social medication.

Figure 1.

(a) Percentage mortality (mean ± s.d.) of Varroa mites reared in artificial cells treated with propolis ethanol extract (V+P+E+) or with ethanol only (V+P−E+, positive control) or left untreated (V+P−E−, negative control). (b) Percentage of surviving mites that produced offspring (i.e. fertility; mean ± s.d.) in artificial cells treated with an ethanolic extract of propolis (V+P+E+) or with ethanol only (V+P−E+, positive control) or left untreated (V+P−E−, negative control). Two asterisks mark experimental groups differing from each other at p < 0.01; three asterisks were used if p < 0.001.

Figure 2.

(a) Proportion of bees (mean ± s.d.) showing the characteristic symptoms of high viral infection levels which emerged from rearing cells treated or not with propolis (P+/P−) and infested or not with a mite (V+/V−). Bars marked with a different letter are significantly different at p < 0.05. (b) Survival of mite-infested (V+) and uninfested (V−) honeybees, from artificial rearing cells treated or not with propolis (P+/P−).

Figure 3.

(a) Preference of mite-infested (V+) and uninfested bees (V−) for a propolis-enriched diet over a sugar only diet (mean ± s.d.). Two asterisks mark experimental groups differing at p < 0.01. Generalized linear mixed-effects models: Z-value = 2.852, p = 0.004. (b) Survival of adult bees that were infested with a mite or not at the pupal stage (V+/V−) and fed as adults with propolis or not (P+/P−).