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Assessing Effects of Sunflower Pollen on a Gut Pathogen Infection in Multiple Bee Species

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Abstract
Pathogens have been identified as a major contributor to the widespread decline of some bee species, making understanding host-pathogen dynamics a crucial area of research. Sunflower pollen (Helianthus annuus L.; Asterales: Asteraceae) dramatically and consistently reduces infection by a prevalent gut pathogen, Crithidia bombi (Lipa & Triggiani 1988) (Kinetoplastida: Trypanosomatidae), in the common eastern bumble bee Bombus impatiens (Cresson 1863). In a laboratory experiment, we asked whether feeding bumble bees sunflower pollen diets prior to pathogen exposure decreases C. bombi infection. We found that consuming a sunflower pollen diet before inoculation did not reduce C. bombi cell counts compared to buckwheat pollen, a negative control pollen. The results show no evidence of sunflower pollen providing prophylactic resistance against C. bombi infection, indicating that the timing at which sunflower pollen is consumed relative to exposure has important consequences for infection. Relatively little is known about whether sunflower pollen or sunflower plantings reduce infection in other bee species. In a field study, we asked: (1) Does C. bombi infection intensity differ between bumble bee species and two solitary bee species on sunflower farms? (2) In B. impatiens and Bombus griseocollis, does sunflower abundance on farms correlate with C. bombi infection intensity? (3) Do bumble bees and solitary bees differ in their collection of sunflower pollen on sunflower farms, and does this correlate with infection intensity? All bumble bee species sampled carried C. bombi infection. Bombus vagans/sandersoni/perplexus, B. bimaculatus, and B. griseocollis all had significantly higher infection intensity than B. impatiens. A novel finding included the detection of viable C. bombi cells in 3 out of 160 wild Melissodes trinodis sampled. We did not find C. bombi cells in any of 171 Halictus ligatus sampled. A relationship between sunflower abundance and C. bombi infection intensity was not found in any of the bee species. Solitary species carried a higher proportion of sunflower pollen than bumble bee species. The results demonstrate significant variation in infection intensity and sunflower pollen collection among bee species and may inform new methods to investigate pathogen presence in bee species on farms.
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Thesis (Open Access)
Date
2024-09
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Attribution-NonCommercial-NoDerivatives 4.0 International
License
http://creativecommons.org/licenses/by-nc-nd/4.0/
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