Dietary Phytochemicals, Honey Bee Longevity and Pathogen Tolerance

Abstract

Continued loss of natural habitats with native prairies and wildflower patches is eliminating diverse sources of pollen, nectar and phytochemicals therein for foraging bees. The longstanding plant-pollinator mutualism reiterates the role of phytochemicals in sustaining plant-pollinator relationship and promoting honey bee health. We studied the effects of four phytochemicals-caffeine, gallic acid, kaempferol and p-coumaric acid, on survival and pathogen tolerance in the European honey bee, Apis mellifera (L.). We recorded longevity of worker bees that were provided ad libitum access to sugar solution supplemented with different concentrations of phytochemicals. We artificially infected worker bees with the protozoan parasite, Nosema ceranae. Infected bees were provided access to the same concentrations of the phytochemicals in the sugar solution, and their longevity and spore load at mortality were determined. Bees supplemented with dietary phytochemicals survived longer and lower concentrations were generally more beneficial. Dietary phytochemicals enabled bees to combat infection as seen by reduced spore-load at mortality. Many of the phytochemicals are plant defense compounds that pollinators have evolved to tolerate and derive benefits from. Our findings support the chemical bases of co-evolutionary interactions and reiterate the importance of diversity in floral nutrition sources to sustain healthy honey bee populations by strengthening the natural mutualistic relationships.

Keywords: Apis mellifera; Nosema ceranae; honey bees; nectar; phytochemicals; plant-pollinator interactions.

Figure 1

Survival proportions (A) and median longevity (B) of bees fed ad libitum with sucrose solutions supplemented with phytochemicals at different concentrations. Kaplan Maier Survival Analyses and log-rank (Mantel-Cox) pairwise comparisons were used to compare survival rates between Control and different concentrations within each phytochemical compound (p < 0.0001 is denoted ***; p = 0.01 is denoted by *; p > 0.5 is denoted by ns; numbers indicate sample sizes (above treatment bars and below ● respectively). Pairwise comparisons between compounds and doses are provided in Supplement S1.

Figure 2

Spore loads (untransformed values) in dead infected bees (A) and median longevity of bees (B) that received dietary supplementation of phytochemicals at different concentrations (N = 30 bees for each phytochemical treatment; N = 22 for Control). Bars with different letters are significantly different from the control (Spore loads (A): GLM Univariate ANOVA followed by Tukey’s post-hoc comparison of log-transformed spore loads; Longevity (B): Median test).