title: Bumble bee parasite strains vary in resistance to phytochemicals.
abstract: Nectar and pollen contain diverse phytochemicals that can reduce disease in pollinators. However, prior studies showed variable effects of nectar chemicals on infection, which could reflect variable phytochemical resistance among parasite strains. Inter-strain variation in resistance could influence evolutionary interactions between plants, pollinators, and pollinator disease, but testing direct effects of phytochemicals on parasites requires elimination of variation between bees. Using cell cultures of the bumble bee parasite Crithidia bombi, we determined (1) growth-inhibiting effects of nine floral phytochemicals and (2) variation in phytochemical resistance among four parasite strains. C. bombi growth was unaffected by naturally occurring concentrations of the known antitrypanosomal phenolics gallic acid, caffeic acid, and chlorogenic acid. However, C. bombi growth was inhibited by anabasine, eugenol, and thymol. Strains varied >3-fold in phytochemical resistance, suggesting that selection for phytochemical resistance could drive parasite evolution. Inhibitory concentrations of thymol (4.53-22.2 ppm) were similar to concentrations in Thymus vulgaris nectar (mean 5.2 ppm). Exposure of C. bombi to naturally occurring levels of phytochemicals-either within bees or during parasite transmission via flowers-could influence infection in nature. Flowers that produce antiparasitic phytochemicals, including thymol, could potentially reduce infection in Bombus populations, thereby counteracting a possible contributor to pollinator decline.
authors.affiliation: Department of Biology, University of Massachusetts at Amherst, Amherst, Massachusetts 01003, United States.
authors.forename: Evan C
authors.initials: EC
authors.lastname: Palmer-Young
authors.affiliation: School of Biological Sciences, Illinois State University, Normal, Illinois 61790, United States.
authors.forename: Ben M
authors.initials: BM
authors.lastname: Sadd
authors.affiliation: Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AE, United Kingdom.|University of Greenwich, Medway, ME4 4TB, United Kingdom.
authors.forename: Philip C
authors.initials: PC
authors.lastname: Stevenson
authors.affiliation: Department of Applied Ecology, North Carolina State University, Raleigh, North Carolina 27695, United States.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Irwin
authors.affiliation: Department of Biology, University of Massachusetts at Amherst, Amherst, Massachusetts 01003, United States.
authors.forename: Lynn S
authors.initials: LS
authors.lastname: Adler
mesh_terms: D000691:Anabasine / Q000494:pharmacology; D000818:Animals; D001516:Bees / Q000469:parasitology*; D002478:Cells, Cultured; D003421:Crithidia / Q000187:drug effects / Q000472:pathogenicity* / Q000502:physiology*; D005054:Eugenol / Q000494:pharmacology; D006790:Host-Parasite Interactions; D064209:Phytochemicals / Q000494:pharmacology*; D013943:Thymol / Q000494:pharmacology; D046930:Thymus Plant / Q000737:chemistry
chemical_list: D064209:Phytochemicals; D013943:Thymol; D005054:Eugenol; D000691:Anabasine