The impact of consuming biologically active compounds is often dose-dependent, where small quantities can be medicinal while larger doses are toxic. The consumption of plant secondary compounds can be toxic to herbivores in large doses, but can also improve survival in parasitized herbivores. In addition, recent studies have found that consuming
nectar secondary compounds may decrease parasite loads in pollinators. However, the effect of compound dose on bee survival and parasite loads has not been assessed. To determine how secondary compound consumption affects survival and pathogen load in Bombus impatiens, we manipulated the presence of a common gut parasite, Crithidia bombi, and dietary concentration of
anabasine, a
nectar alkaloid produced by Nicotiana spp. using four concentrations naturally observed in floral
nectar. We hypothesized that increased consumption of secondary compounds at concentrations found in nature would decrease survival of uninfected bees, but improve survival and ameliorate parasite loads in infected bees. We found medicinal effects of
anabasine in infected bees; the high-
anabasine diet decreased parasite loads and increased the probability of clearing the
infection entirely. However, survival time was not affected by any level of
anabasine concentration, or by interactive effects of
anabasine concentration and
infection. Crithidia
infection reduced survival time by more than two days, but this effect was not significant. Our results support a medicinal role for
anabasine at the highest concentration; moreover, we found no evidence for a survival-related cost of
anabasine consumption across the concentration range found in
nectar. Our results suggest that consuming
anabasine at the higher levels of the natural range could reduce or clear pathogen loads without incurring costs for healthy bees.