The effects of raw propolis on Varroa-infested honey bee (Apis mellifera) workers

Abstract

Self-medication plays a major role in the behavioral defense against pathogens and parasites that animals have developed during evolution. The conditions defining this adaptive behavior are: (1) contact with the substance in question must be deliberate; (2) the substance must be detrimental to one or more parasites; (3) the detrimental effect on parasites must lead to increased host fitness. Recent studies have shown that A. mellifera colonies are able to increase resin foraging rates when infested by V. destructor, whereas further investigations are needed for evidence of parasite and host fitness. In order to understand whether Varroa-infested colonies could benefit from increasing levels of resin, we carried out laboratory bioassays to investigate the effects of propolis on the fitness of infested workers. The longevity and energetic stress of adult bees kept in experimental cages and artificially infested with the mite were thus monitored over time. At the same time, in vitro experiments were performed to study the contact effects of crude propolis on Varroa mites. Our results clearly demonstrate the positive effects of raw propolis on the lifespan of Varroa-infested adult bees. A low narcoleptic effect (19-22%) of raw propolis on phoretic mites after 5 h was also observed. In terms of energetic stress, we found no differences between Varroa-free and Varroa-infested bees in terms of the daily sucrose solution demand. Our findings seem to confirm the hypothesis that resin collection and propolis use in the hive represent an example of self-medication behavior in social insects.

Propolis Consumption Reduces Nosema ceranae Infection of European Honey Bees (Apis mellifera)

“…Secondly, we ascertained whether infected bees were more attracted to a diet containing propolis and consumed a greater proportion of this diet in comparison to uninfected bees. Considering that the biological properties of propolis have mainly been associated with its phenolic components [43,[58][59][60], we also quantified the polyphenol content together with the main phenolic compounds of the propolis used in our bioassays.…”

The effects of crude propolis, its volatiles and ethanolic extracts on the ecto-parasitic mite, Varroa destructor and health of the African savannah honey bee, Apis mellifera scutellata

“…Our results corroborate with those of previous studies in European honey bee colonies, which also reported no significant effects of the natural propolis envelope on mite loads using either our same or larger sample size of six colonies (Borba et al ., 2015; Drescher et al ., 2017). In contrast to this and previous findings, Pusceddu et al found that the quantity of resin collected by the European honey bee, A. mellifera ligustica correlated with the levels of mite infestation (Pusceddu et al ., 2018). These contrasting effects of natural propolis on mite-infestation levels could be a result of the variable chemical composition of the resinous fraction of propolis in the differential geographical areas where these studies were conducted.…”

“…This suggests that the bioactive compounds found in the resinous fraction of propolis are both non-volatile given the bath temperature and reduced pressure during rotatory evaporation, and relatively polar since extracted into ethanol. Pusceddu et al (2018) noted narcotic effects on mites exposed to crude propolis samples collected from A. m. ligustica colonies, though as they suggested, these effects were minimal when compared to those caused by the ethanolic extracts of propolis samples collected from other A. mellifera colonies (Garedew et al, 2002;Damiani et al, 2010).…”

The Strong Anti-Kinetoplastid Properties of Bee Propolis: Composition and Identification of the Active Agents and Their Biochemical Targets

“…For instance, Argentinian propolis was found to be very effective against Varroa [89]. Furthermore, ethanolic extracts of German propolis were highly toxic to Varroa destructor, with a 10% w/v solution being lethal at 5 s contact [90], and Pusceddu et al observed that raw propolis highly significantly increased the lifespan of Varroa-infected bees, almost completely reversing Varroa-associated mortality [91]. Moreover, the addition of natural propolis to hives reduced the titer of Varroa-transmitted deformed wing virus (DWV) [92] and Varroa-infected colonies specifically increased resin foraging [93].…”

“…Moreover, the addition of natural propolis to hives reduced the titer of Varroa-transmitted deformed wing virus (DWV) [92] and Varroa-infected colonies specifically increased resin foraging [93]. It is not yet clear which chemical agents in propolis reduce the impact of Varroa infestation, but it was reported that the total polyphenolic content of propolis correlated with levels of Varroa infection in experimental hives in Sardinia [91]. Caffeic acid and pentenyl caffeates were found to be more abundant in propolis from Varroa-susceptible colonies [94], but this association requires further investigation in order to be confirmed as causal.…”