Context-Dependent Medicinal Effects of Anabasine and Infection-Dependent Toxicity in Bumble Bees

Background Floral phytochemicals are ubiquitous in nature, and can function both as antimicrobials and as insecticides. Although many phytochemicals act as toxins and deterrents to consumers, the same chemicals may counteract disease and be preferred by infected individuals. The roles of nectar and pollen phytochemicals in pollinator ecology and conservation are complex, with evidence for both toxicity and medicinal effects against parasites. However, it remains unclear how consistent the effects of phytochemicals are across different parasite lineages and environmental conditions, and whether pollinators actively self-medicate with these compounds when infected. Approach Here, we test effects of the nectar alkaloid anabasine, found in Nicotiana, on infection intensity, dietary preference, and survival and performance of bumble bees (Bombus impatiens). We examined variation in the effects of anabasine on infection with different lineages of the intestinal parasite Crithidia under pollen-fed and pollen-starved conditions. Results We found that anabasine did not reduce infection intensity in individual bees infected with any of four Crithidia lineages that were tested in parallel, nor did anabasine reduce infection intensity in microcolonies of queenless workers. In addition, neither anabasine nor its isomer, nicotine, was preferred by infected bees in choice experiments, and infected bees consumed less anabasine than did uninfected bees under no-choice conditions. Furthermore, anabasine exacerbated the negative effects of infection on bee survival and microcolony performance. Anabasine reduced infection in only one experiment, in which bees were deprived of pollen and post-pupal contact with nestmates. In this experiment, anabasine had antiparasitic effects in bees from only two of four colonies, and infected bees exhibited reduced—rather than increased—phytochemical consumption relative to uninfected bees. Conclusions Variation in the effect of anabasine on infection suggests potential modulation of tritrophic interactions by both host genotype and environmental variables. Overall, our results demonstrate that Bombus impatiens prefer diets without nicotine and anabasine, and suggest that the medicinal effects and toxicity of anabasine may be context dependent. Future research should identify the specific environmental and genotypic factors that determine whether nectar phytochemicals have medicinal or deleterious effects on pollinators

Plant secondary metabolites enhance survival and pathogen tolerance in the European honey bee: a structure-function study

2019 Spring.Includes bibliographical references.Adequate nutrition is essential for European honey bee (Apis mellifera) colony growth, and productivity, yet foraging limitations resulting from factors such as habitat loss often lead to dietary deficiencies. Plant secondary metabolites are key constituents of floral nectar that support physiological processes in honey bees, however, these compounds are only available to bees with access to a diversity of floral resources. Furthermore, the relationship between different classes of plant secondary metabolites and their function within honey bee diets requires further investigation. Using a structure-function framework, we evaluated whether four structurally similar plant secondary metabolites found in the nectar of common agricultural crops elicit comparable effects on honey bee survival and pathogen tolerance. The addition of plant secondary metabolites to artificial nectar solution enhanced median survival, in some cases more than doubling the lifespan of worker honey bees. Moreover, plant secondary metabolites demonstrated nutraceutical effects, and sometimes elicited medicinal effects on honey bees infected with Nosema ceranae. Our findings provide a platform to identify plant secondary metabolites which can augment current management techniques to support the long-term sustainability of the apiculture industry