Secondary metabolites in floral nectar reduce parasite infections in bumblebees

Abstract

The synthesis of secondary metabolites is a hallmark of plant defence against herbivores. These compounds may be detrimental to consumers, but can also protect herbivores against parasites. Floral nectar commonly contains secondary metabolites, but little is known about the impacts of nectar chemistry on pollinators, including bees. We hypothesized that nectar secondary metabolites could reduce bee parasite infection. We inoculated individual bumblebees with Crithidia bombi, an intestinal parasite, and tested effects of eight naturally occurring nectar chemicals on parasite population growth. Secondary metabolites strongly reduced parasite load, with significant effects of alkaloids, terpenoids and iridoid glycosides ranging from 61 to 81%. Using microcolonies, we also investigated costs and benefits of consuming anabasine, the compound with the strongest effect on parasites, in infected and uninfected bees. Anabasine increased time to egg laying, and Crithidia reduced bee survival. However, anabasine consumption did not mitigate the negative effects of Crithidia, and Crithidia infection did not alter anabasine consumption. Our novel results highlight that although secondary metabolites may not rescue survival in infected bees, they may play a vital role in mediating Crithidia transmission within and between colonies by reducing Crithidia infection intensities.

Pharmacophagy and pharmacophory: mechanisms of self-medication and disease prevention in the honeybee colony (Apis mellifera)

“…chrysin, galangin, pinocembrin, quercetin, kaempferol and tectochrysin) are linked with decreased parasite and pathogen loads in infected individuals. Recent studies report the antimicrobial potential of alkaloids, terpenoids and iridoid glycosides against a gut disease (Crithidia bombi ) of bumblebees (Baracchi et al 2015;Manson et al 2010;Richardson et al 2015). Studies on secondary plant metabolites in nectar should be extended to all groups of bee diseases to better understand the pharmacophagic potential of highly diverse foraging sites shared by honey and bumblebees collecting nectar and pollen.…”

Bumble bee parasite strains vary in resistance to phytochemicals

“…In pollinators, ingestion of floral phytochemicals19 and certain types of honey20 were therapeutic for infected honey bees ( Apis mellifera ). Infection also stimulated collection of phytochemical-rich resins21 and preference for high-phytochemical nectar2223, indicating the potential for phytochemicals to improve pollinator health.…”

“…that decreases queen survival and colony fitness29 and may exacerbate the negative effects of pesticides30 and nutritional stress31. Crithidia bombi encounters phytochemicals throughout its life cycle, making it a relevant system for testing the effects of phytochemicals on pollinator infection22233233. Parasites infect new hosts via transmission at flowers10 and within bee hives32, which contain derivatives of nectar, pollen, and other plant materials21.…”

Bees use the taste of pollen to determine which flowers to visit

“…For example, nectar can contain secondary compounds that limit its consumption, with consequences for both plant and pollinator fitness [1,2]. Pollinators also collect pollen, yet how pollen might influence pollinator preferences has received considerably less attention.…”