Context-dependent medicinal effects of anabasine and infection-dependent toxicity in bumble bees

Abstract

BackgroundFloral 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.ApproachHere, 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.ResultsWe 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.ConclusionsVariation 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.

Effects of short‐term exposure to naturally occurring thymol concentrations on transmission of a bumble bee parasite

“…Number of inoculum drops probed during the trial also did not explain significant variation in infection intensity (β = 0.10 ± 0.07 SE, Table 1). Wing size was negatively correlated with infection intensity (β = -1.56 ± 0.59 SE, Table 1), indicative of lower infection intensity in larger bees, which is consistent with previous results (Manson et al 2010, Palmer-Young, Hogeboom, Kaye, et al 2017.…”

Effect of timing and exposure of sunflower pollen on a common gut pathogen of bumble bees

“…A polyfloral pollen diet reduced Nosema ceranae (Microsporidia, Nosematidae, Zander) infections and improved longevity in infected honey bees (Apis mellifera L.; Apidae) compared with a monofloral diet (Alaux et al, 2010;Di Pasquale et al, 2013). Palmer-Young et al 2017). Palmer-Young et al 2017).…”

“…Floral chemistry may also play important roles mediating bee disease; several nectar secondary compounds reduced C. bombi in B. impatiens (Manson et al, 2009;Baracchi et al, 2015;Richardson et al, 2015), although this is not always the case (e.g. Palmer-Young et al 2017). In addition, sunflower (Helianthus annuus L.; Asteraceae) honey reduced N. ceranae in honey bees compared with other types of honey (Gherman et al, 2014).…”

Quantitative Assessment of Nectar Microbe-Produced Volatiles

“…Plant-produced compounds may be toxic or deterrent to pollinators or may impact bee learning, memory and behavior (29)(30)(31)(32). Nectar secondary metabolites can also reduce disease incidence in bees but in other cases, may exacerbate infection (33)(34)(35). Application of beneficial nectar microbes capable of selectively degrading harmful compounds from nectar could influence pollinator health and increase pollination services.…”