Abstract
Parasites and pathogens of the honey bee (Apis mellifera) are key factors underlying colony losses, which are threatening the beekeeping industry and agriculture as a whole. To control the spread and development of pathogen infections within the colony, honey bees use plant resins with antibiotic activity, but little is known about the properties of other substances, that are mainly used as a foodstuff, for controlling possible diseases both at the individual and colony level. In this study, we tested the hypothesis that pollen is beneficial for honey bees challenged with the parasitic mite Varroa destructor associated to the Deformed Wing Virus. First, we studied the effects of pollen on the survival of infested bees, under laboratory and field conditions, and observed that a pollen rich diet can compensate the deleterious effects of mite parasitization. Subsequently, we characterized the pollen compounds responsible for the observed positive effects. Finally, based on the results of a transcriptomic analysis of parasitized bees fed with pollen or not, we developed a comprehensive framework for interpreting the observed effects of pollen on honey bee health, which incorporates the possible effects on cuticle integrity, energetic metabolism and immune response.
Highlights
Animal self-medication is receiving increasing attention[1, 2] due to its profound implications for host-parasite interactions, including the effects on parasite transmission and the evolution of parasite virulence and host defences
To determine if access to pollen can mitigate the adverse effects of a parasitic infestation, we reared honey bee larvae inside artificial cells in presence of a Varroa mite (V+) or not (V−), and maintained the emerging adults in cages under standardized environmental conditions to evaluate survival under two different diet regimes: a sugar diet complemented with pollen (P+) and a sugar diet (P−), supplied ad libitum
In bees that were infested with Varroa, access to pollen significantly increased the lifespan relative to parasitized bees reared with sugar alone (Fig. 1; V+P+ vs V+P−, Log Rank (Chi Square = 26.8, d.f. = 1, P < 0.001))
Summary
Animal self-medication is receiving increasing attention[1, 2] due to its profound implications for host-parasite interactions, including the effects on parasite transmission and the evolution of parasite virulence and host defences. Previous studies tested whether dietary protein quantity and diversity can influence bees’ immunocompetence and found that protein feeding modifies both individual and social immunocompetence as measured by assessing haemocyte concentration, fat body content, phenoloxidase activity and glucose oxidase[11]. These results were expanded by Alaux and coworkers, who carried out a transcriptomic study of bees fed a rich diet made of pollen and sugar and a poor diet of sugar alone, demonstrating that beside activating nutrient-sensing and metabolic pathways, pollen positively influence expression of genes involved in the production of some antimicrobial peptides and longevity[12], corroborating previous studies[13]. The hive hosts a complex cohort of symbionts that can be propagated by the mites invading the brood cells or attaching to adult bees[23]
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