Data from: Disease where you dine: plant species and floral traits associated with pathogen transmission in bumble bees

Hotspots of disease transmission can strongly influence pathogen spread.
Bee pathogens may be transmitted via shared floral use, but the role of
plant species and floral trait variation in shaping transmission dynamics
is almost entirely unexplored. Given the importance of pathogens for the
decline of several bee species, understanding whether and how plant
species and floral traits affect transmission could give us important
tools for predicting which plant species may be hotspots for disease
spread. We assessed variation in transmission via susceptibility
(probability of infection) and mean intensity (cell count of infected
bees) of the trypanosomatid gut pathogen Crithidia bombi to uninfected
Bombus impatiens workers foraging on 14 plant species, and assessed the
role of floral traits, bee size and foraging behavior on transmission. We
also conducted a manipulative experiment to determine how the number of
open flowers affected transmission on three plant species, Penstemon
digitalis, Monarda didyma, and Lythrum salicaria. Plant species differed
fourfold in the overall mean abundance of Crithidia in foraging bumble
bees (mean including infected and uninfected bees). Across plant species,
bee susceptibility and mean intensity increased with the number of
reproductive structures per inflorescence (buds, flowers and fruits);
smaller bees and those that foraged longer were also more susceptible.
Trait-based models were as good or better than species-based models at
predicting susceptibility and mean intensity based on AIC values.
Surprisingly, floral size and morphology did not significantly predict
transmission across species. In the manipulative experiment, more open
flowers increased mean pathogen abundance fourfold in Monarda, but had no
effect in the other two plant species. Our results suggest that variation
among plant species, through their influence on pathogen transmission, may
shape bee disease dynamics. Given widespread investment in
pollinator-friendly plantings to support pollinators, understanding how
plant species affect disease transmission is important for recommending
plant species that optimize pollinator health.