Table 1.

Experiment 1: plant secondary metabolites naturally occurring in floral nectar tested for effects on the gut pathogen Crithidia bombi when consumed by its host, Bombus impatiens. (Compound concentrations were chosen based on reports of occurrence in floral nectar, except gallic acid and thymol, for which we estimated values from concentrations reported in Apis mellifera honey, and aucubin and catalpol, which are unpublished data. We report main effects for ANCOVAs comparing parasite load of bees consuming each compound to those of controls. Statistically significant differences: *p ≤ 0.05; **p ≤ 0.01 and ***p ≤ 0.001.)

compound	concentration (ppm)	exemplar plants	refs	treatment effect
alkaloids
anabasine	5.0	Nicotiana glauca	[17]	F1,26 = 13.77, p = 0.001***
caffeine	98.0	Citrus spp., Coffea spp., Camellia oleifera	[12,18,19]	F1,21 = 0.50, p = 0.49
nicotine	2.0	Nicotiana glauca	[17]	F1,29 = 7.67, p = 0.01**
cyanogenic glycosides
amygdalin	50.0	Prunus amygdalus	[20]	F1,53 = 0.19, p = 0.67
iridoid glycosides
aucubin	1600.0	Chelone glabra	M. D. Bowers 2012, pers. comm.	F1,44 = 2.15, p = 0.15
catalpol	1417.0	Chelone glabra	M. D. Bowers 2012, pers. comm.	F1,44 = 3.89, p = 0.05*
phenolics
gallic acid	50.0	Fagopyrum esculentum	[21]	F1,38 = 1.38, p = 0.25
terpenoids
thymol	0.2	Tilia europea	[22]	F1,38 = 7.89, p = 0.01**