title: 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.
authors.affiliation: Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA leif.richardson@uvm.edu.
authors.forename: Leif L
authors.identifier: http://orcid.org/0000-0003-4855-5737
authors.initials: LL
authors.lastname: Richardson
authors.affiliation: Biology Department, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Lynn S
authors.initials: LS
authors.lastname: Adler
authors.affiliation: Biology Department, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Anne S
authors.initials: AS
authors.lastname: Leonard
authors.affiliation: Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Andicoechea
authors.affiliation: Biology Department, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Karly H
authors.initials: KH
authors.lastname: Regan
authors.affiliation: Biology Department, University of Massachusetts, Amherst, MA 01003, USA.
authors.forename: Winston E
authors.initials: WE
authors.lastname: Anthony
authors.affiliation: Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
authors.forename: Jessamyn S
authors.initials: JS
authors.lastname: Manson
authors.affiliation: Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Irwin
mesh_terms: D000470:Alkaloids; D000691:Anabasine; D000818:Animals; D001516:Bees / Q000469:parasitology* / Q000502:physiology; D003421:Crithidia; D060467:Disease Resistance; D006027:Glycosides; D006790:Host-Parasite Interactions; D057048:Plant Nectar / Q000737:chemistry*; D064210:Secondary Metabolism; D013729:Terpenes
chemical_list: D000470:Alkaloids; D006027:Glycosides; D057048:Plant Nectar; D013729:Terpenes; D000691:Anabasine
keywords: Crithidia bombi; bumblebees; parasitism; plant secondary metabolites; pollination; tritrophic interactions