Effect of timing and exposure of sunflower pollen on a common gut pathogen of bumble bees

Abstract

1. Several bee species are declining due to multiple factors, including pathogens. Ingestion of sunflower (Helianthus annuus) pollen can dramatically reduce the bumble bee gut pathogen Crithidia bombi, but little is known about how timing and exposure to sunflower pollen consumption affects pathogen load.2. Two experiments were carried out to investigate how exposure to sunflower pollen relative to pathogen exposure affects Crithidia bombi in Bombus impatiens. Foraging trials with pollen-producing and male-sterile (pollen absent) sunflower lines were performed to investigate whether sunflower pollen affected pathogen transmission in a single foraging bout, and 7-day laboratory trials were done to investigate whether timing and duration of exposure to sunflower pollen after infection affected C. bombi.3. In foraging trials, pollen presence on inflorescences inoculated with C. bombi did not affect transmission (pathogen cell counts of foraging workers) 1 week later, suggesting that a brief experience with sunflower pollen concurrent with pathogen exposure is insufficient to reduce infection. In laboratory trials, consuming sunflower pollen for the first 3.5 days or all 7 days after infection reduced cell counts compared with a negative control pollen, but consuming sunflower pollen starting 3.5 days after infection did not. Consuming sunflower pollen for 7 days was significantly and substantially more effective than any other treatment. Thus, both duration and timing of exposure to sunflower pollen may affect pathogen load.4. These results are important for understanding ecological disease dynamics in natural settings with free-flying bumble bees, and may inform decisions about using medicinal diets to manage bumble bee health commercially.

Assessing Chemical Mechanisms Underlying the Effects of Sunflower Pollen on a Gut Pathogen in Bumble Bees

“…We isolated major secondary compounds of sunflower and tested their efficacy against a common bumble bee gut pathogen; we also assessed the effects of numerous fatty acids from sunflower pollen, singly and in combination. Although we found that sunflower pollen consistently reduced Crithidia compared to control pollens, matching previous work (Giacomini et al 2018;LoCascio et al 2019a;LoCascio et al 2019b), none of the compounds we tested appear to be the sole mechanism driving this result, as none of them significantly reduced pathogen counts relative to control pollens. Although we did not test protein content in this study, it seems unlikely that protein content is the underlying mechanism since protein concentrations are similarly low in buckwheat and sunflower pollen (Yang et al 2013) but outcomes of these diets for Crithidia infection are very different.…”

Honey Bee (Hymenoptera: Apidea) Pollen Forage in a Highly Cultivated Agroecosystem: Limited Diet Diversity and Its Relationship to Virus Resistance

“…Some native plants can be planted in agricultural land dominated by corn and soybean to increase forage diversity in early season. For example, sunflower ( Helianthus annuus L. [Asterales: Asteraceae]) can have medication effect on bees, and could be an option for forage enhancement ( Jonathan et al 2018 , LoCascio et al 2019 ). Efforts to conserve beneficial insects have revealed that native plants commonly found in prairies, the dominant habitat in Iowa before European settlement, are highly attractive to native pollinators as well as managed honey bees ( Tuell et al 2008 , Blaauw and Isaacs 2014 ).…”

Understanding effects of floral products on bee parasites: Mechanisms, synergism, and ecological complexity

“…The timing and duration of exposure to antiparasitic floral products can strongly influence the strength of their inhibitory effects, as we have already seen with the example of callunene in heather nectar ( Koch et al, 2019 ). In another example, while the consumption of sunflower pollen over the span of one week dramatically reduced C. bombi infection in B. impatiens workers, sunflower pollen consumption limited to a 3.5 day period had less inhibitory effect, particularly if consumption was delayed for several days after initial infection ( LoCascio et al, 2019b ). Moreover, one-time consumption of sunflower pollen at the time of infection had no effect on ultimate infection intensity ( LoCascio et al, 2019b ).…”